Updating go depencancies. Switching to go1.6 vendoring (#2949)

12 files changed, 2502 insertions, 0 deletions

diff --git a/vendor/golang.org/x/image/LICENSE b/vendor/golang.org/x/image/LICENSE
new file mode 100644
index 000000000..6a66aea5e
--- /dev/null
+++ b/vendor/golang.org/x/image/LICENSE
@@ -0,0 +1,27 @@
+Copyright (c) 2009 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/vendor/golang.org/x/image/PATENTS b/vendor/golang.org/x/image/PATENTS
new file mode 100644
index 000000000..733099041
--- /dev/null
+++ b/vendor/golang.org/x/image/PATENTS
@@ -0,0 +1,22 @@
+Additional IP Rights Grant (Patents)
+
+"This implementation" means the copyrightable works distributed by
+Google as part of the Go project.
+
+Google hereby grants to You a perpetual, worldwide, non-exclusive,
+no-charge, royalty-free, irrevocable (except as stated in this section)
+patent license to make, have made, use, offer to sell, sell, import,
+transfer and otherwise run, modify and propagate the contents of this
+implementation of Go, where such license applies only to those patent
+claims, both currently owned or controlled by Google and acquired in
+the future, licensable by Google that are necessarily infringed by this
+implementation of Go.  This grant does not include claims that would be
+infringed only as a consequence of further modification of this
+implementation.  If you or your agent or exclusive licensee institute or
+order or agree to the institution of patent litigation against any
+entity (including a cross-claim or counterclaim in a lawsuit) alleging
+that this implementation of Go or any code incorporated within this
+implementation of Go constitutes direct or contributory patent
+infringement, or inducement of patent infringement, then any patent
+rights granted to you under this License for this implementation of Go
+shall terminate as of the date such litigation is filed.
diff --git a/vendor/golang.org/x/image/bmp/reader.go b/vendor/golang.org/x/image/bmp/reader.go
new file mode 100644
index 000000000..a48cba84d
--- /dev/null
+++ b/vendor/golang.org/x/image/bmp/reader.go
@@ -0,0 +1,199 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package bmp implements a BMP image decoder and encoder.
+//
+// The BMP specification is at http://www.digicamsoft.com/bmp/bmp.html.
+package bmp
+
+import (
+	"errors"
+	"image"
+	"image/color"
+	"io"
+)
+
+// ErrUnsupported means that the input BMP image uses a valid but unsupported
+// feature.
+var ErrUnsupported = errors.New("bmp: unsupported BMP image")
+
+func readUint16(b []byte) uint16 {
+	return uint16(b[0]) | uint16(b[1])<<8
+}
+
+func readUint32(b []byte) uint32 {
+	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
+}
+
+// decodePaletted reads an 8 bit-per-pixel BMP image from r.
+// If topDown is false, the image rows will be read bottom-up.
+func decodePaletted(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
+	paletted := image.NewPaletted(image.Rect(0, 0, c.Width, c.Height), c.ColorModel.(color.Palette))
+	if c.Width == 0 || c.Height == 0 {
+		return paletted, nil
+	}
+	var tmp [4]byte
+	y0, y1, yDelta := c.Height-1, -1, -1
+	if topDown {
+		y0, y1, yDelta = 0, c.Height, +1
+	}
+	for y := y0; y != y1; y += yDelta {
+		p := paletted.Pix[y*paletted.Stride : y*paletted.Stride+c.Width]
+		if _, err := io.ReadFull(r, p); err != nil {
+			return nil, err
+		}
+		// Each row is 4-byte aligned.
+		if c.Width%4 != 0 {
+			_, err := io.ReadFull(r, tmp[:4-c.Width%4])
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+	return paletted, nil
+}
+
+// decodeRGB reads a 24 bit-per-pixel BMP image from r.
+// If topDown is false, the image rows will be read bottom-up.
+func decodeRGB(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
+	rgba := image.NewRGBA(image.Rect(0, 0, c.Width, c.Height))
+	if c.Width == 0 || c.Height == 0 {
+		return rgba, nil
+	}
+	// There are 3 bytes per pixel, and each row is 4-byte aligned.
+	b := make([]byte, (3*c.Width+3)&^3)
+	y0, y1, yDelta := c.Height-1, -1, -1
+	if topDown {
+		y0, y1, yDelta = 0, c.Height, +1
+	}
+	for y := y0; y != y1; y += yDelta {
+		if _, err := io.ReadFull(r, b); err != nil {
+			return nil, err
+		}
+		p := rgba.Pix[y*rgba.Stride : y*rgba.Stride+c.Width*4]
+		for i, j := 0, 0; i < len(p); i, j = i+4, j+3 {
+			// BMP images are stored in BGR order rather than RGB order.
+			p[i+0] = b[j+2]
+			p[i+1] = b[j+1]
+			p[i+2] = b[j+0]
+			p[i+3] = 0xFF
+		}
+	}
+	return rgba, nil
+}
+
+// decodeNRGBA reads a 32 bit-per-pixel BMP image from r.
+// If topDown is false, the image rows will be read bottom-up.
+func decodeNRGBA(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
+	rgba := image.NewNRGBA(image.Rect(0, 0, c.Width, c.Height))
+	if c.Width == 0 || c.Height == 0 {
+		return rgba, nil
+	}
+	y0, y1, yDelta := c.Height-1, -1, -1
+	if topDown {
+		y0, y1, yDelta = 0, c.Height, +1
+	}
+	for y := y0; y != y1; y += yDelta {
+		p := rgba.Pix[y*rgba.Stride : y*rgba.Stride+c.Width*4]
+		if _, err := io.ReadFull(r, p); err != nil {
+			return nil, err
+		}
+		for i := 0; i < len(p); i += 4 {
+			// BMP images are stored in BGRA order rather than RGBA order.
+			p[i+0], p[i+2] = p[i+2], p[i+0]
+		}
+	}
+	return rgba, nil
+}
+
+// Decode reads a BMP image from r and returns it as an image.Image.
+// Limitation: The file must be 8, 24 or 32 bits per pixel.
+func Decode(r io.Reader) (image.Image, error) {
+	c, bpp, topDown, err := decodeConfig(r)
+	if err != nil {
+		return nil, err
+	}
+	switch bpp {
+	case 8:
+		return decodePaletted(r, c, topDown)
+	case 24:
+		return decodeRGB(r, c, topDown)
+	case 32:
+		return decodeNRGBA(r, c, topDown)
+	}
+	panic("unreachable")
+}
+
+// DecodeConfig returns the color model and dimensions of a BMP image without
+// decoding the entire image.
+// Limitation: The file must be 8, 24 or 32 bits per pixel.
+func DecodeConfig(r io.Reader) (image.Config, error) {
+	config, _, _, err := decodeConfig(r)
+	return config, err
+}
+
+func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown bool, err error) {
+	// We only support those BMP images that are a BITMAPFILEHEADER
+	// immediately followed by a BITMAPINFOHEADER.
+	const (
+		fileHeaderLen = 14
+		infoHeaderLen = 40
+	)
+	var b [1024]byte
+	if _, err := io.ReadFull(r, b[:fileHeaderLen+infoHeaderLen]); err != nil {
+		return image.Config{}, 0, false, err
+	}
+	if string(b[:2]) != "BM" {
+		return image.Config{}, 0, false, errors.New("bmp: invalid format")
+	}
+	offset := readUint32(b[10:14])
+	if readUint32(b[14:18]) != infoHeaderLen {
+		return image.Config{}, 0, false, ErrUnsupported
+	}
+	width := int(int32(readUint32(b[18:22])))
+	height := int(int32(readUint32(b[22:26])))
+	if height < 0 {
+		height, topDown = -height, true
+	}
+	if width < 0 || height < 0 {
+		return image.Config{}, 0, false, ErrUnsupported
+	}
+	// We only support 1 plane, 8 or 24 bits per pixel and no compression.
+	planes, bpp, compression := readUint16(b[26:28]), readUint16(b[28:30]), readUint32(b[30:34])
+	if planes != 1 || compression != 0 {
+		return image.Config{}, 0, false, ErrUnsupported
+	}
+	switch bpp {
+	case 8:
+		if offset != fileHeaderLen+infoHeaderLen+256*4 {
+			return image.Config{}, 0, false, ErrUnsupported
+		}
+		_, err = io.ReadFull(r, b[:256*4])
+		if err != nil {
+			return image.Config{}, 0, false, err
+		}
+		pcm := make(color.Palette, 256)
+		for i := range pcm {
+			// BMP images are stored in BGR order rather than RGB order.
+			// Every 4th byte is padding.
+			pcm[i] = color.RGBA{b[4*i+2], b[4*i+1], b[4*i+0], 0xFF}
+		}
+		return image.Config{ColorModel: pcm, Width: width, Height: height}, 8, topDown, nil
+	case 24:
+		if offset != fileHeaderLen+infoHeaderLen {
+			return image.Config{}, 0, false, ErrUnsupported
+		}
+		return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 24, topDown, nil
+	case 32:
+		if offset != fileHeaderLen+infoHeaderLen {
+			return image.Config{}, 0, false, ErrUnsupported
+		}
+		return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 32, topDown, nil
+	}
+	return image.Config{}, 0, false, ErrUnsupported
+}
+
+func init() {
+	image.RegisterFormat("bmp", "BM????\x00\x00\x00\x00", Decode, DecodeConfig)
+}
diff --git a/vendor/golang.org/x/image/bmp/writer.go b/vendor/golang.org/x/image/bmp/writer.go
new file mode 100644
index 000000000..6947968a4
--- /dev/null
+++ b/vendor/golang.org/x/image/bmp/writer.go
@@ -0,0 +1,166 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package bmp
+
+import (
+	"encoding/binary"
+	"errors"
+	"image"
+	"io"
+)
+
+type header struct {
+	sigBM           [2]byte
+	fileSize        uint32
+	resverved       [2]uint16
+	pixOffset       uint32
+	dibHeaderSize   uint32
+	width           uint32
+	height          uint32
+	colorPlane      uint16
+	bpp             uint16
+	compression     uint32
+	imageSize       uint32
+	xPixelsPerMeter uint32
+	yPixelsPerMeter uint32
+	colorUse        uint32
+	colorImportant  uint32
+}
+
+func encodePaletted(w io.Writer, pix []uint8, dx, dy, stride, step int) error {
+	var padding []byte
+	if dx < step {
+		padding = make([]byte, step-dx)
+	}
+	for y := dy - 1; y >= 0; y-- {
+		min := y*stride + 0
+		max := y*stride + dx
+		if _, err := w.Write(pix[min:max]); err != nil {
+			return err
+		}
+		if padding != nil {
+			if _, err := w.Write(padding); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func encodeRGBA(w io.Writer, pix []uint8, dx, dy, stride, step int) error {
+	buf := make([]byte, step)
+	for y := dy - 1; y >= 0; y-- {
+		min := y*stride + 0
+		max := y*stride + dx*4
+		off := 0
+		for i := min; i < max; i += 4 {
+			buf[off+2] = pix[i+0]
+			buf[off+1] = pix[i+1]
+			buf[off+0] = pix[i+2]
+			off += 3
+		}
+		if _, err := w.Write(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func encode(w io.Writer, m image.Image, step int) error {
+	b := m.Bounds()
+	buf := make([]byte, step)
+	for y := b.Max.Y - 1; y >= b.Min.Y; y-- {
+		off := 0
+		for x := b.Min.X; x < b.Max.X; x++ {
+			r, g, b, _ := m.At(x, y).RGBA()
+			buf[off+2] = byte(r >> 8)
+			buf[off+1] = byte(g >> 8)
+			buf[off+0] = byte(b >> 8)
+			off += 3
+		}
+		if _, err := w.Write(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Encode writes the image m to w in BMP format.
+func Encode(w io.Writer, m image.Image) error {
+	d := m.Bounds().Size()
+	if d.X < 0 || d.Y < 0 {
+		return errors.New("bmp: negative bounds")
+	}
+	h := &header{
+		sigBM:         [2]byte{'B', 'M'},
+		fileSize:      14 + 40,
+		pixOffset:     14 + 40,
+		dibHeaderSize: 40,
+		width:         uint32(d.X),
+		height:        uint32(d.Y),
+		colorPlane:    1,
+	}
+
+	var step int
+	var palette []byte
+	switch m := m.(type) {
+	case *image.Gray:
+		step = (d.X + 3) &^ 3
+		palette = make([]byte, 1024)
+		for i := 0; i < 256; i++ {
+			palette[i*4+0] = uint8(i)
+			palette[i*4+1] = uint8(i)
+			palette[i*4+2] = uint8(i)
+			palette[i*4+3] = 0xFF
+		}
+		h.imageSize = uint32(d.Y * step)
+		h.fileSize += uint32(len(palette)) + h.imageSize
+		h.pixOffset += uint32(len(palette))
+		h.bpp = 8
+
+	case *image.Paletted:
+		step = (d.X + 3) &^ 3
+		palette = make([]byte, 1024)
+		for i := 0; i < len(m.Palette) && i < 256; i++ {
+			r, g, b, _ := m.Palette[i].RGBA()
+			palette[i*4+0] = uint8(b >> 8)
+			palette[i*4+1] = uint8(g >> 8)
+			palette[i*4+2] = uint8(r >> 8)
+			palette[i*4+3] = 0xFF
+		}
+		h.imageSize = uint32(d.Y * step)
+		h.fileSize += uint32(len(palette)) + h.imageSize
+		h.pixOffset += uint32(len(palette))
+		h.bpp = 8
+	default:
+		step = (3*d.X + 3) &^ 3
+		h.imageSize = uint32(d.Y * step)
+		h.fileSize += h.imageSize
+		h.bpp = 24
+	}
+
+	if err := binary.Write(w, binary.LittleEndian, h); err != nil {
+		return err
+	}
+	if palette != nil {
+		if err := binary.Write(w, binary.LittleEndian, palette); err != nil {
+			return err
+		}
+	}
+
+	if d.X == 0 || d.Y == 0 {
+		return nil
+	}
+
+	switch m := m.(type) {
+	case *image.Gray:
+		return encodePaletted(w, m.Pix, d.X, d.Y, m.Stride, step)
+	case *image.Paletted:
+		return encodePaletted(w, m.Pix, d.X, d.Y, m.Stride, step)
+	case *image.RGBA:
+		return encodeRGBA(w, m.Pix, d.X, d.Y, m.Stride, step)
+	}
+	return encode(w, m, step)
+}
diff --git a/vendor/golang.org/x/image/font/font.go b/vendor/golang.org/x/image/font/font.go
new file mode 100644
index 000000000..57fd61bdc
--- /dev/null
+++ b/vendor/golang.org/x/image/font/font.go
@@ -0,0 +1,230 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package font defines an interface for font faces, for drawing text on an
+// image.
+//
+// Other packages provide font face implementations. For example, a truetype
+// package would provide one based on .ttf font files.
+package font
+
+import (
+	"image"
+	"image/draw"
+	"io"
+
+	"golang.org/x/image/math/fixed"
+)
+
+// TODO: who is responsible for caches (glyph images, glyph indices, kerns)?
+// The Drawer or the Face?
+
+// Face is a font face. Its glyphs are often derived from a font file, such as
+// "Comic_Sans_MS.ttf", but a face has a specific size, style, weight and
+// hinting. For example, the 12pt and 18pt versions of Comic Sans are two
+// different faces, even if derived from the same font file.
+//
+// A Face is not safe for concurrent use by multiple goroutines, as its methods
+// may re-use implementation-specific caches and mask image buffers.
+//
+// To create a Face, look to other packages that implement specific font file
+// formats.
+type Face interface {
+	io.Closer
+
+	// Glyph returns the draw.DrawMask parameters (dr, mask, maskp) to draw r's
+	// glyph at the sub-pixel destination location dot, and that glyph's
+	// advance width.
+	//
+	// It returns !ok if the face does not contain a glyph for r.
+	//
+	// The contents of the mask image returned by one Glyph call may change
+	// after the next Glyph call. Callers that want to cache the mask must make
+	// a copy.
+	Glyph(dot fixed.Point26_6, r rune) (
+		dr image.Rectangle, mask image.Image, maskp image.Point, advance fixed.Int26_6, ok bool)
+
+	// GlyphBounds returns the bounding box of r's glyph, drawn at a dot equal
+	// to the origin, and that glyph's advance width.
+	//
+	// It returns !ok if the face does not contain a glyph for r.
+	//
+	// The glyph's ascent and descent equal -bounds.Min.Y and +bounds.Max.Y. A
+	// visual depiction of what these metrics are is at
+	// https://developer.apple.com/library/mac/documentation/TextFonts/Conceptual/CocoaTextArchitecture/Art/glyph_metrics_2x.png
+	GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool)
+
+	// GlyphAdvance returns the advance width of r's glyph.
+	//
+	// It returns !ok if the face does not contain a glyph for r.
+	GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool)
+
+	// Kern returns the horizontal adjustment for the kerning pair (r0, r1). A
+	// positive kern means to move the glyphs further apart.
+	Kern(r0, r1 rune) fixed.Int26_6
+
+	// Metrics returns the metrics for this Face.
+	Metrics() Metrics
+
+	// TODO: ColoredGlyph for various emoji?
+	// TODO: Ligatures? Shaping?
+}
+
+// Metrics holds the metrics for a Face. A visual depiction is at
+// https://developer.apple.com/library/mac/documentation/TextFonts/Conceptual/CocoaTextArchitecture/Art/glyph_metrics_2x.png
+type Metrics struct {
+	// Height is the recommended amount of vertical space between two lines of
+	// text.
+	Height fixed.Int26_6
+
+	// Ascent is the distance from the top of a line to its baseline.
+	Ascent fixed.Int26_6
+
+	// Descent is the distance from the bottom of a line to its baseline. The
+	// value is typically positive, even though a descender goes below the
+	// baseline.
+	Descent fixed.Int26_6
+}
+
+// TODO: Drawer.Layout or Drawer.Measure methods to measure text without
+// drawing?
+
+// Drawer draws text on a destination image.
+//
+// A Drawer is not safe for concurrent use by multiple goroutines, since its
+// Face is not.
+type Drawer struct {
+	// Dst is the destination image.
+	Dst draw.Image
+	// Src is the source image.
+	Src image.Image
+	// Face provides the glyph mask images.
+	Face Face
+	// Dot is the baseline location to draw the next glyph. The majority of the
+	// affected pixels will be above and to the right of the dot, but some may
+	// be below or to the left. For example, drawing a 'j' in an italic face
+	// may affect pixels below and to the left of the dot.
+	Dot fixed.Point26_6
+
+	// TODO: Clip image.Image?
+	// TODO: SrcP image.Point for Src images other than *image.Uniform? How
+	// does it get updated during DrawString?
+}
+
+// TODO: should DrawString return the last rune drawn, so the next DrawString
+// call can kern beforehand? Or should that be the responsibility of the caller
+// if they really want to do that, since they have to explicitly shift d.Dot
+// anyway?
+//
+// In general, we'd have a DrawBytes([]byte) and DrawRuneReader(io.RuneReader)
+// and the last case can't assume that you can rewind the stream.
+//
+// TODO: how does this work with line breaking: drawing text up until a
+// vertical line? Should DrawString return the number of runes drawn?
+
+// DrawString draws s at the dot and advances the dot's location.
+func (d *Drawer) DrawString(s string) {
+	var prevC rune
+	for i, c := range s {
+		if i != 0 {
+			d.Dot.X += d.Face.Kern(prevC, c)
+		}
+		dr, mask, maskp, advance, ok := d.Face.Glyph(d.Dot, c)
+		if !ok {
+			// TODO: is falling back on the U+FFFD glyph the responsibility of
+			// the Drawer or the Face?
+			// TODO: set prevC = '\ufffd'?
+			continue
+		}
+		draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
+		d.Dot.X += advance
+		prevC = c
+	}
+}
+
+// MeasureString returns how far dot would advance by drawing s.
+func (d *Drawer) MeasureString(s string) (advance fixed.Int26_6) {
+	return MeasureString(d.Face, s)
+}
+
+// MeasureString returns how far dot would advance by drawing s with f.
+func MeasureString(f Face, s string) (advance fixed.Int26_6) {
+	var prevC rune
+	for i, c := range s {
+		if i != 0 {
+			advance += f.Kern(prevC, c)
+		}
+		a, ok := f.GlyphAdvance(c)
+		if !ok {
+			// TODO: is falling back on the U+FFFD glyph the responsibility of
+			// the Drawer or the Face?
+			// TODO: set prevC = '\ufffd'?
+			continue
+		}
+		advance += a
+		prevC = c
+	}
+	return advance
+}
+
+// Hinting selects how to quantize a vector font's glyph nodes.
+//
+// Not all fonts support hinting.
+type Hinting int
+
+const (
+	HintingNone Hinting = iota
+	HintingVertical
+	HintingFull
+)
+
+// Stretch selects a normal, condensed, or expanded face.
+//
+// Not all fonts support stretches.
+type Stretch int
+
+const (
+	StretchUltraCondensed Stretch = -4
+	StretchExtraCondensed Stretch = -3
+	StretchCondensed      Stretch = -2
+	StretchSemiCondensed  Stretch = -1
+	StretchNormal         Stretch = +0
+	StretchSemiExpanded   Stretch = +1
+	StretchExpanded       Stretch = +2
+	StretchExtraExpanded  Stretch = +3
+	StretchUltraExpanded  Stretch = +4
+)
+
+// Style selects a normal, italic, or oblique face.
+//
+// Not all fonts support styles.
+type Style int
+
+const (
+	StyleNormal Style = iota
+	StyleItalic
+	StyleOblique
+)
+
+// Weight selects a normal, light or bold face.
+//
+// Not all fonts support weights.
+//
+// The named Weight constants (e.g. WeightBold) correspond to CSS' common
+// weight names (e.g. "Bold"), but the numerical values differ, so that in Go,
+// the zero value means to use a normal weight. For the CSS names and values,
+// see https://developer.mozilla.org/en/docs/Web/CSS/font-weight
+type Weight int
+
+const (
+	WeightThin       Weight = -3 // CSS font-weight value 100.
+	WeightExtraLight Weight = -2 // CSS font-weight value 200.
+	WeightLight      Weight = -1 // CSS font-weight value 300.
+	WeightNormal     Weight = +0 // CSS font-weight value 400.
+	WeightMedium     Weight = +1 // CSS font-weight value 500.
+	WeightSemiBold   Weight = +2 // CSS font-weight value 600.
+	WeightBold       Weight = +3 // CSS font-weight value 700.
+	WeightExtraBold  Weight = +4 // CSS font-weight value 800.
+	WeightBlack      Weight = +5 // CSS font-weight value 900.
+)
diff --git a/vendor/golang.org/x/image/math/fixed/fixed.go b/vendor/golang.org/x/image/math/fixed/fixed.go
new file mode 100644
index 000000000..cc7bac79e
--- /dev/null
+++ b/vendor/golang.org/x/image/math/fixed/fixed.go
@@ -0,0 +1,202 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package fixed implements fixed-point integer types.
+package fixed
+
+import (
+	"fmt"
+)
+
+// TODO: implement fmt.Formatter for %f and %g.
+
+// I returns the integer value i as an Int26_6.
+//
+// For example, passing the integer value 2 yields Int26_6(128).
+func I(i int) Int26_6 {
+	return Int26_6(i << 6)
+}
+
+// Int26_6 is a signed 26.6 fixed-point number.
+//
+// The integer part ranges from -33554432 to 33554431, inclusive. The
+// fractional part has 6 bits of precision.
+//
+// For example, the number one-and-a-quarter is Int26_6(1<<6 + 1<<4).
+type Int26_6 int32
+
+// String returns a human-readable representation of a 26.6 fixed-point number.
+//
+// For example, the number one-and-a-quarter becomes "1:16".
+func (x Int26_6) String() string {
+	const shift, mask = 6, 1<<6 - 1
+	if x >= 0 {
+		return fmt.Sprintf("%d:%02d", int32(x>>shift), int32(x&mask))
+	}
+	x = -x
+	if x >= 0 {
+		return fmt.Sprintf("-%d:%02d", int32(x>>shift), int32(x&mask))
+	}
+	return "-33554432:00" // The minimum value is -(1<<25).
+}
+
+// Floor returns the greatest integer value less than or equal to x.
+//
+// Its return type is int, not Int26_6.
+func (x Int26_6) Floor() int { return int((x + 0x00) >> 6) }
+
+// Round returns the nearest integer value to x. Ties are rounded up.
+//
+// Its return type is int, not Int26_6.
+func (x Int26_6) Round() int { return int((x + 0x20) >> 6) }
+
+// Ceil returns the least integer value greater than or equal to x.
+//
+// Its return type is int, not Int26_6.
+func (x Int26_6) Ceil() int { return int((x + 0x3f) >> 6) }
+
+// Int52_12 is a signed 52.12 fixed-point number.
+//
+// The integer part ranges from -2251799813685248 to 2251799813685247,
+// inclusive. The fractional part has 12 bits of precision.
+//
+// For example, the number one-and-a-quarter is Int52_12(1<<12 + 1<<10).
+type Int52_12 int64
+
+// String returns a human-readable representation of a 52.12 fixed-point
+// number.
+//
+// For example, the number one-and-a-quarter becomes "1:1024".
+func (x Int52_12) String() string {
+	const shift, mask = 12, 1<<12 - 1
+	if x >= 0 {
+		return fmt.Sprintf("%d:%04d", int64(x>>shift), int64(x&mask))
+	}
+	x = -x
+	if x >= 0 {
+		return fmt.Sprintf("-%d:%04d", int64(x>>shift), int64(x&mask))
+	}
+	return "-2251799813685248:0000" // The minimum value is -(1<<51).
+}
+
+// Floor returns the greatest integer value less than or equal to x.
+//
+// Its return type is int, not Int52_12.
+func (x Int52_12) Floor() int { return int((x + 0x000) >> 12) }
+
+// Round returns the nearest integer value to x. Ties are rounded up.
+//
+// Its return type is int, not Int52_12.
+func (x Int52_12) Round() int { return int((x + 0x800) >> 12) }
+
+// Ceil returns the least integer value greater than or equal to x.
+//
+// Its return type is int, not Int52_12.
+func (x Int52_12) Ceil() int { return int((x + 0xfff) >> 12) }
+
+// P returns the integer values x and y as a Point26_6.
+//
+// For example, passing the integer values (2, -3) yields Point26_6{128, -192}.
+func P(x, y int) Point26_6 {
+	return Point26_6{Int26_6(x << 6), Int26_6(y << 6)}
+}
+
+// Point26_6 is a 26.6 fixed-point coordinate pair.
+//
+// It is analogous to the image.Point type in the standard library.
+type Point26_6 struct {
+	X, Y Int26_6
+}
+
+// Add returns the vector p+q.
+func (p Point26_6) Add(q Point26_6) Point26_6 {
+	return Point26_6{p.X + q.X, p.Y + q.Y}
+}
+
+// Sub returns the vector p-q.
+func (p Point26_6) Sub(q Point26_6) Point26_6 {
+	return Point26_6{p.X - q.X, p.Y - q.Y}
+}
+
+// Mul returns the vector p*k.
+func (p Point26_6) Mul(k Int26_6) Point26_6 {
+	return Point26_6{p.X * k / 64, p.Y * k / 64}
+}
+
+// Div returns the vector p/k.
+func (p Point26_6) Div(k Int26_6) Point26_6 {
+	return Point26_6{p.X * 64 / k, p.Y * 64 / k}
+}
+
+// Point52_12 is a 52.12 fixed-point coordinate pair.
+//
+// It is analogous to the image.Point type in the standard library.
+type Point52_12 struct {
+	X, Y Int52_12
+}
+
+// Add returns the vector p+q.
+func (p Point52_12) Add(q Point52_12) Point52_12 {
+	return Point52_12{p.X + q.X, p.Y + q.Y}
+}
+
+// Sub returns the vector p-q.
+func (p Point52_12) Sub(q Point52_12) Point52_12 {
+	return Point52_12{p.X - q.X, p.Y - q.Y}
+}
+
+// Mul returns the vector p*k.
+func (p Point52_12) Mul(k Int52_12) Point52_12 {
+	return Point52_12{p.X * k / 4096, p.Y * k / 4096}
+}
+
+// Div returns the vector p/k.
+func (p Point52_12) Div(k Int52_12) Point52_12 {
+	return Point52_12{p.X * 4096 / k, p.Y * 4096 / k}
+}
+
+// R returns the integer values minX, minY, maxX, maxY as a Rectangle26_6.
+//
+// For example, passing the integer values (0, 1, 2, 3) yields
+// Rectangle26_6{Point26_6{0, 64}, Point26_6{128, 192}}.
+//
+// Like the image.Rect function in the standard library, the returned rectangle
+// has minimum and maximum coordinates swapped if necessary so that it is
+// well-formed.
+func R(minX, minY, maxX, maxY int) Rectangle26_6 {
+	if minX > maxX {
+		minX, maxX = maxX, minX
+	}
+	if minY > maxY {
+		minY, maxY = maxY, minY
+	}
+	return Rectangle26_6{
+		Point26_6{
+			Int26_6(minX << 6),
+			Int26_6(minY << 6),
+		},
+		Point26_6{
+			Int26_6(maxX << 6),
+			Int26_6(maxY << 6),
+		},
+	}
+}
+
+// Rectangle26_6 is a 26.6 fixed-point coordinate rectangle. The Min bound is
+// inclusive and the Max bound is exclusive. It is well-formed if Min.X <=
+// Max.X and likewise for Y.
+//
+// It is analogous to the image.Rectangle type in the standard library.
+type Rectangle26_6 struct {
+	Min, Max Point26_6
+}
+
+// Rectangle52_12 is a 52.12 fixed-point coordinate rectangle. The Min bound is
+// inclusive and the Max bound is exclusive. It is well-formed if Min.X <=
+// Max.X and likewise for Y.
+//
+// It is analogous to the image.Rectangle type in the standard library.
+type Rectangle52_12 struct {
+	Min, Max Point52_12
+}
diff --git a/vendor/golang.org/x/image/tiff/buffer.go b/vendor/golang.org/x/image/tiff/buffer.go
new file mode 100644
index 000000000..d1801be48
--- /dev/null
+++ b/vendor/golang.org/x/image/tiff/buffer.go
@@ -0,0 +1,69 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tiff
+
+import "io"
+
+// buffer buffers an io.Reader to satisfy io.ReaderAt.
+type buffer struct {
+	r   io.Reader
+	buf []byte
+}
+
+// fill reads data from b.r until the buffer contains at least end bytes.
+func (b *buffer) fill(end int) error {
+	m := len(b.buf)
+	if end > m {
+		if end > cap(b.buf) {
+			newcap := 1024
+			for newcap < end {
+				newcap *= 2
+			}
+			newbuf := make([]byte, end, newcap)
+			copy(newbuf, b.buf)
+			b.buf = newbuf
+		} else {
+			b.buf = b.buf[:end]
+		}
+		if n, err := io.ReadFull(b.r, b.buf[m:end]); err != nil {
+			end = m + n
+			b.buf = b.buf[:end]
+			return err
+		}
+	}
+	return nil
+}
+
+func (b *buffer) ReadAt(p []byte, off int64) (int, error) {
+	o := int(off)
+	end := o + len(p)
+	if int64(end) != off+int64(len(p)) {
+		return 0, io.ErrUnexpectedEOF
+	}
+
+	err := b.fill(end)
+	return copy(p, b.buf[o:end]), err
+}
+
+// Slice returns a slice of the underlying buffer. The slice contains
+// n bytes starting at offset off.
+func (b *buffer) Slice(off, n int) ([]byte, error) {
+	end := off + n
+	if err := b.fill(end); err != nil {
+		return nil, err
+	}
+	return b.buf[off:end], nil
+}
+
+// newReaderAt converts an io.Reader into an io.ReaderAt.
+func newReaderAt(r io.Reader) io.ReaderAt {
+	if ra, ok := r.(io.ReaderAt); ok {
+		return ra
+	}
+	return &buffer{
+		r:   r,
+		buf: make([]byte, 0, 1024),
+	}
+}
diff --git a/vendor/golang.org/x/image/tiff/compress.go b/vendor/golang.org/x/image/tiff/compress.go
new file mode 100644
index 000000000..3f176f00a
--- /dev/null
+++ b/vendor/golang.org/x/image/tiff/compress.go
@@ -0,0 +1,58 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tiff
+
+import (
+	"bufio"
+	"io"
+)
+
+type byteReader interface {
+	io.Reader
+	io.ByteReader
+}
+
+// unpackBits decodes the PackBits-compressed data in src and returns the
+// uncompressed data.
+//
+// The PackBits compression format is described in section 9 (p. 42)
+// of the TIFF spec.
+func unpackBits(r io.Reader) ([]byte, error) {
+	buf := make([]byte, 128)
+	dst := make([]byte, 0, 1024)
+	br, ok := r.(byteReader)
+	if !ok {
+		br = bufio.NewReader(r)
+	}
+
+	for {
+		b, err := br.ReadByte()
+		if err != nil {
+			if err == io.EOF {
+				return dst, nil
+			}
+			return nil, err
+		}
+		code := int(int8(b))
+		switch {
+		case code >= 0:
+			n, err := io.ReadFull(br, buf[:code+1])
+			if err != nil {
+				return nil, err
+			}
+			dst = append(dst, buf[:n]...)
+		case code == -128:
+			// No-op.
+		default:
+			if b, err = br.ReadByte(); err != nil {
+				return nil, err
+			}
+			for j := 0; j < 1-code; j++ {
+				buf[j] = b
+			}
+			dst = append(dst, buf[:1-code]...)
+		}
+	}
+}
diff --git a/vendor/golang.org/x/image/tiff/consts.go b/vendor/golang.org/x/image/tiff/consts.go
new file mode 100644
index 000000000..3c51a70be
--- /dev/null
+++ b/vendor/golang.org/x/image/tiff/consts.go
@@ -0,0 +1,133 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tiff
+
+// A tiff image file contains one or more images. The metadata
+// of each image is contained in an Image File Directory (IFD),
+// which contains entries of 12 bytes each and is described
+// on page 14-16 of the specification. An IFD entry consists of
+//
+//  - a tag, which describes the signification of the entry,
+//  - the data type and length of the entry,
+//  - the data itself or a pointer to it if it is more than 4 bytes.
+//
+// The presence of a length means that each IFD is effectively an array.
+
+const (
+	leHeader = "II\x2A\x00" // Header for little-endian files.
+	beHeader = "MM\x00\x2A" // Header for big-endian files.
+
+	ifdLen = 12 // Length of an IFD entry in bytes.
+)
+
+// Data types (p. 14-16 of the spec).
+const (
+	dtByte     = 1
+	dtASCII    = 2
+	dtShort    = 3
+	dtLong     = 4
+	dtRational = 5
+)
+
+// The length of one instance of each data type in bytes.
+var lengths = [...]uint32{0, 1, 1, 2, 4, 8}
+
+// Tags (see p. 28-41 of the spec).
+const (
+	tImageWidth                = 256
+	tImageLength               = 257
+	tBitsPerSample             = 258
+	tCompression               = 259
+	tPhotometricInterpretation = 262
+
+	tStripOffsets    = 273
+	tSamplesPerPixel = 277
+	tRowsPerStrip    = 278
+	tStripByteCounts = 279
+
+	tTileWidth      = 322
+	tTileLength     = 323
+	tTileOffsets    = 324
+	tTileByteCounts = 325
+
+	tXResolution    = 282
+	tYResolution    = 283
+	tResolutionUnit = 296
+
+	tPredictor    = 317
+	tColorMap     = 320
+	tExtraSamples = 338
+	tSampleFormat = 339
+)
+
+// Compression types (defined in various places in the spec and supplements).
+const (
+	cNone       = 1
+	cCCITT      = 2
+	cG3         = 3 // Group 3 Fax.
+	cG4         = 4 // Group 4 Fax.
+	cLZW        = 5
+	cJPEGOld    = 6 // Superseded by cJPEG.
+	cJPEG       = 7
+	cDeflate    = 8 // zlib compression.
+	cPackBits   = 32773
+	cDeflateOld = 32946 // Superseded by cDeflate.
+)
+
+// Photometric interpretation values (see p. 37 of the spec).
+const (
+	pWhiteIsZero = 0
+	pBlackIsZero = 1
+	pRGB         = 2
+	pPaletted    = 3
+	pTransMask   = 4 // transparency mask
+	pCMYK        = 5
+	pYCbCr       = 6
+	pCIELab      = 8
+)
+
+// Values for the tPredictor tag (page 64-65 of the spec).
+const (
+	prNone       = 1
+	prHorizontal = 2
+)
+
+// Values for the tResolutionUnit tag (page 18).
+const (
+	resNone    = 1
+	resPerInch = 2 // Dots per inch.
+	resPerCM   = 3 // Dots per centimeter.
+)
+
+// imageMode represents the mode of the image.
+type imageMode int
+
+const (
+	mBilevel imageMode = iota
+	mPaletted
+	mGray
+	mGrayInvert
+	mRGB
+	mRGBA
+	mNRGBA
+)
+
+// CompressionType describes the type of compression used in Options.
+type CompressionType int
+
+const (
+	Uncompressed CompressionType = iota
+	Deflate
+)
+
+// specValue returns the compression type constant from the TIFF spec that
+// is equivalent to c.
+func (c CompressionType) specValue() uint32 {
+	switch c {
+	case Deflate:
+		return cDeflate
+	}
+	return cNone
+}
diff --git a/vendor/golang.org/x/image/tiff/lzw/reader.go b/vendor/golang.org/x/image/tiff/lzw/reader.go
new file mode 100644
index 000000000..dc9f7dd1d
--- /dev/null
+++ b/vendor/golang.org/x/image/tiff/lzw/reader.go
@@ -0,0 +1,277 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package lzw implements the Lempel-Ziv-Welch compressed data format,
+// described in T. A. Welch, ``A Technique for High-Performance Data
+// Compression'', Computer, 17(6) (June 1984), pp 8-19.
+//
+// In particular, it implements LZW as used by the TIFF file format, including
+// an "off by one" algorithmic difference when compared to standard LZW.
+package lzw
+
+/*
+This file was branched from src/pkg/compress/lzw/reader.go in the
+standard library. Differences from the original are marked with "NOTE".
+
+The tif_lzw.c file in the libtiff C library has this comment:
+
+----
+The 5.0 spec describes a different algorithm than Aldus
+implements.  Specifically, Aldus does code length transitions
+one code earlier than should be done (for real LZW).
+Earlier versions of this library implemented the correct
+LZW algorithm, but emitted codes in a bit order opposite
+to the TIFF spec.  Thus, to maintain compatibility w/ Aldus
+we interpret MSB-LSB ordered codes to be images written w/
+old versions of this library, but otherwise adhere to the
+Aldus "off by one" algorithm.
+----
+
+The Go code doesn't read (invalid) TIFF files written by old versions of
+libtiff, but the LZW algorithm in this package still differs from the one in
+Go's standard package library to accomodate this "off by one" in valid TIFFs.
+*/
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// Order specifies the bit ordering in an LZW data stream.
+type Order int
+
+const (
+	// LSB means Least Significant Bits first, as used in the GIF file format.
+	LSB Order = iota
+	// MSB means Most Significant Bits first, as used in the TIFF and PDF
+	// file formats.
+	MSB
+)
+
+const (
+	maxWidth           = 12
+	decoderInvalidCode = 0xffff
+	flushBuffer        = 1 << maxWidth
+)
+
+// decoder is the state from which the readXxx method converts a byte
+// stream into a code stream.
+type decoder struct {
+	r        io.ByteReader
+	bits     uint32
+	nBits    uint
+	width    uint
+	read     func(*decoder) (uint16, error) // readLSB or readMSB
+	litWidth int                            // width in bits of literal codes
+	err      error
+
+	// The first 1<<litWidth codes are literal codes.
+	// The next two codes mean clear and EOF.
+	// Other valid codes are in the range [lo, hi] where lo := clear + 2,
+	// with the upper bound incrementing on each code seen.
+	// overflow is the code at which hi overflows the code width. NOTE: TIFF's LZW is "off by one".
+	// last is the most recently seen code, or decoderInvalidCode.
+	clear, eof, hi, overflow, last uint16
+
+	// Each code c in [lo, hi] expands to two or more bytes. For c != hi:
+	//   suffix[c] is the last of these bytes.
+	//   prefix[c] is the code for all but the last byte.
+	//   This code can either be a literal code or another code in [lo, c).
+	// The c == hi case is a special case.
+	suffix [1 << maxWidth]uint8
+	prefix [1 << maxWidth]uint16
+
+	// output is the temporary output buffer.
+	// Literal codes are accumulated from the start of the buffer.
+	// Non-literal codes decode to a sequence of suffixes that are first
+	// written right-to-left from the end of the buffer before being copied
+	// to the start of the buffer.
+	// It is flushed when it contains >= 1<<maxWidth bytes,
+	// so that there is always room to decode an entire code.
+	output [2 * 1 << maxWidth]byte
+	o      int    // write index into output
+	toRead []byte // bytes to return from Read
+}
+
+// readLSB returns the next code for "Least Significant Bits first" data.
+func (d *decoder) readLSB() (uint16, error) {
+	for d.nBits < d.width {
+		x, err := d.r.ReadByte()
+		if err != nil {
+			return 0, err
+		}
+		d.bits |= uint32(x) << d.nBits
+		d.nBits += 8
+	}
+	code := uint16(d.bits & (1<<d.width - 1))
+	d.bits >>= d.width
+	d.nBits -= d.width
+	return code, nil
+}
+
+// readMSB returns the next code for "Most Significant Bits first" data.
+func (d *decoder) readMSB() (uint16, error) {
+	for d.nBits < d.width {
+		x, err := d.r.ReadByte()
+		if err != nil {
+			return 0, err
+		}
+		d.bits |= uint32(x) << (24 - d.nBits)
+		d.nBits += 8
+	}
+	code := uint16(d.bits >> (32 - d.width))
+	d.bits <<= d.width
+	d.nBits -= d.width
+	return code, nil
+}
+
+func (d *decoder) Read(b []byte) (int, error) {
+	for {
+		if len(d.toRead) > 0 {
+			n := copy(b, d.toRead)
+			d.toRead = d.toRead[n:]
+			return n, nil
+		}
+		if d.err != nil {
+			return 0, d.err
+		}
+		d.decode()
+	}
+}
+
+// decode decompresses bytes from r and leaves them in d.toRead.
+// read specifies how to decode bytes into codes.
+// litWidth is the width in bits of literal codes.
+func (d *decoder) decode() {
+	// Loop over the code stream, converting codes into decompressed bytes.
+	for {
+		code, err := d.read(d)
+		if err != nil {
+			if err == io.EOF {
+				err = io.ErrUnexpectedEOF
+			}
+			d.err = err
+			d.flush()
+			return
+		}
+		switch {
+		case code < d.clear:
+			// We have a literal code.
+			d.output[d.o] = uint8(code)
+			d.o++
+			if d.last != decoderInvalidCode {
+				// Save what the hi code expands to.
+				d.suffix[d.hi] = uint8(code)
+				d.prefix[d.hi] = d.last
+			}
+		case code == d.clear:
+			d.width = 1 + uint(d.litWidth)
+			d.hi = d.eof
+			d.overflow = 1 << d.width
+			d.last = decoderInvalidCode
+			continue
+		case code == d.eof:
+			d.flush()
+			d.err = io.EOF
+			return
+		case code <= d.hi:
+			c, i := code, len(d.output)-1
+			if code == d.hi {
+				// code == hi is a special case which expands to the last expansion
+				// followed by the head of the last expansion. To find the head, we walk
+				// the prefix chain until we find a literal code.
+				c = d.last
+				for c >= d.clear {
+					c = d.prefix[c]
+				}
+				d.output[i] = uint8(c)
+				i--
+				c = d.last
+			}
+			// Copy the suffix chain into output and then write that to w.
+			for c >= d.clear {
+				d.output[i] = d.suffix[c]
+				i--
+				c = d.prefix[c]
+			}
+			d.output[i] = uint8(c)
+			d.o += copy(d.output[d.o:], d.output[i:])
+			if d.last != decoderInvalidCode {
+				// Save what the hi code expands to.
+				d.suffix[d.hi] = uint8(c)
+				d.prefix[d.hi] = d.last
+			}
+		default:
+			d.err = errors.New("lzw: invalid code")
+			d.flush()
+			return
+		}
+		d.last, d.hi = code, d.hi+1
+		if d.hi+1 >= d.overflow { // NOTE: the "+1" is where TIFF's LZW differs from the standard algorithm.
+			if d.width == maxWidth {
+				d.last = decoderInvalidCode
+			} else {
+				d.width++
+				d.overflow <<= 1
+			}
+		}
+		if d.o >= flushBuffer {
+			d.flush()
+			return
+		}
+	}
+}
+
+func (d *decoder) flush() {
+	d.toRead = d.output[:d.o]
+	d.o = 0
+}
+
+var errClosed = errors.New("lzw: reader/writer is closed")
+
+func (d *decoder) Close() error {
+	d.err = errClosed // in case any Reads come along
+	return nil
+}
+
+// NewReader creates a new io.ReadCloser.
+// Reads from the returned io.ReadCloser read and decompress data from r.
+// If r does not also implement io.ByteReader,
+// the decompressor may read more data than necessary from r.
+// It is the caller's responsibility to call Close on the ReadCloser when
+// finished reading.
+// The number of bits to use for literal codes, litWidth, must be in the
+// range [2,8] and is typically 8. It must equal the litWidth
+// used during compression.
+func NewReader(r io.Reader, order Order, litWidth int) io.ReadCloser {
+	d := new(decoder)
+	switch order {
+	case LSB:
+		d.read = (*decoder).readLSB
+	case MSB:
+		d.read = (*decoder).readMSB
+	default:
+		d.err = errors.New("lzw: unknown order")
+		return d
+	}
+	if litWidth < 2 || 8 < litWidth {
+		d.err = fmt.Errorf("lzw: litWidth %d out of range", litWidth)
+		return d
+	}
+	if br, ok := r.(io.ByteReader); ok {
+		d.r = br
+	} else {
+		d.r = bufio.NewReader(r)
+	}
+	d.litWidth = litWidth
+	d.width = 1 + uint(litWidth)
+	d.clear = uint16(1) << uint(litWidth)
+	d.eof, d.hi = d.clear+1, d.clear+1
+	d.overflow = uint16(1) << d.width
+	d.last = decoderInvalidCode
+
+	return d
+}
diff --git a/vendor/golang.org/x/image/tiff/reader.go b/vendor/golang.org/x/image/tiff/reader.go
new file mode 100644
index 000000000..714e3dda7
--- /dev/null
+++ b/vendor/golang.org/x/image/tiff/reader.go
@@ -0,0 +1,681 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package tiff implements a TIFF image decoder and encoder.
+//
+// The TIFF specification is at http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
+package tiff
+
+import (
+	"compress/zlib"
+	"encoding/binary"
+	"fmt"
+	"image"
+	"image/color"
+	"io"
+	"io/ioutil"
+	"math"
+
+	"golang.org/x/image/tiff/lzw"
+)
+
+// A FormatError reports that the input is not a valid TIFF image.
+type FormatError string
+
+func (e FormatError) Error() string {
+	return "tiff: invalid format: " + string(e)
+}
+
+// An UnsupportedError reports that the input uses a valid but
+// unimplemented feature.
+type UnsupportedError string
+
+func (e UnsupportedError) Error() string {
+	return "tiff: unsupported feature: " + string(e)
+}
+
+// An InternalError reports that an internal error was encountered.
+type InternalError string
+
+func (e InternalError) Error() string {
+	return "tiff: internal error: " + string(e)
+}
+
+var errNoPixels = FormatError("not enough pixel data")
+
+type decoder struct {
+	r         io.ReaderAt
+	byteOrder binary.ByteOrder
+	config    image.Config
+	mode      imageMode
+	bpp       uint
+	features  map[int][]uint
+	palette   []color.Color
+
+	buf   []byte
+	off   int    // Current offset in buf.
+	v     uint32 // Buffer value for reading with arbitrary bit depths.
+	nbits uint   // Remaining number of bits in v.
+}
+
+// firstVal returns the first uint of the features entry with the given tag,
+// or 0 if the tag does not exist.
+func (d *decoder) firstVal(tag int) uint {
+	f := d.features[tag]
+	if len(f) == 0 {
+		return 0
+	}
+	return f[0]
+}
+
+// ifdUint decodes the IFD entry in p, which must be of the Byte, Short
+// or Long type, and returns the decoded uint values.
+func (d *decoder) ifdUint(p []byte) (u []uint, err error) {
+	var raw []byte
+	if len(p) < ifdLen {
+		return nil, FormatError("bad IFD entry")
+	}
+
+	datatype := d.byteOrder.Uint16(p[2:4])
+	if dt := int(datatype); dt <= 0 || dt >= len(lengths) {
+		return nil, UnsupportedError("IFD entry datatype")
+	}
+
+	count := d.byteOrder.Uint32(p[4:8])
+	if count > math.MaxInt32/lengths[datatype] {
+		return nil, FormatError("IFD data too large")
+	}
+	if datalen := lengths[datatype] * count; datalen > 4 {
+		// The IFD contains a pointer to the real value.
+		raw = make([]byte, datalen)
+		_, err = d.r.ReadAt(raw, int64(d.byteOrder.Uint32(p[8:12])))
+	} else {
+		raw = p[8 : 8+datalen]
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	u = make([]uint, count)
+	switch datatype {
+	case dtByte:
+		for i := uint32(0); i < count; i++ {
+			u[i] = uint(raw[i])
+		}
+	case dtShort:
+		for i := uint32(0); i < count; i++ {
+			u[i] = uint(d.byteOrder.Uint16(raw[2*i : 2*(i+1)]))
+		}
+	case dtLong:
+		for i := uint32(0); i < count; i++ {
+			u[i] = uint(d.byteOrder.Uint32(raw[4*i : 4*(i+1)]))
+		}
+	default:
+		return nil, UnsupportedError("data type")
+	}
+	return u, nil
+}
+
+// parseIFD decides whether the the IFD entry in p is "interesting" and
+// stows away the data in the decoder.
+func (d *decoder) parseIFD(p []byte) error {
+	tag := d.byteOrder.Uint16(p[0:2])
+	switch tag {
+	case tBitsPerSample,
+		tExtraSamples,
+		tPhotometricInterpretation,
+		tCompression,
+		tPredictor,
+		tStripOffsets,
+		tStripByteCounts,
+		tRowsPerStrip,
+		tTileWidth,
+		tTileLength,
+		tTileOffsets,
+		tTileByteCounts,
+		tImageLength,
+		tImageWidth:
+		val, err := d.ifdUint(p)
+		if err != nil {
+			return err
+		}
+		d.features[int(tag)] = val
+	case tColorMap:
+		val, err := d.ifdUint(p)
+		if err != nil {
+			return err
+		}
+		numcolors := len(val) / 3
+		if len(val)%3 != 0 || numcolors <= 0 || numcolors > 256 {
+			return FormatError("bad ColorMap length")
+		}
+		d.palette = make([]color.Color, numcolors)
+		for i := 0; i < numcolors; i++ {
+			d.palette[i] = color.RGBA64{
+				uint16(val[i]),
+				uint16(val[i+numcolors]),
+				uint16(val[i+2*numcolors]),
+				0xffff,
+			}
+		}
+	case tSampleFormat:
+		// Page 27 of the spec: If the SampleFormat is present and
+		// the value is not 1 [= unsigned integer data], a Baseline
+		// TIFF reader that cannot handle the SampleFormat value
+		// must terminate the import process gracefully.
+		val, err := d.ifdUint(p)
+		if err != nil {
+			return err
+		}
+		for _, v := range val {
+			if v != 1 {
+				return UnsupportedError("sample format")
+			}
+		}
+	}
+	return nil
+}
+
+// readBits reads n bits from the internal buffer starting at the current offset.
+func (d *decoder) readBits(n uint) (v uint32, ok bool) {
+	for d.nbits < n {
+		d.v <<= 8
+		if d.off >= len(d.buf) {
+			return 0, false
+		}
+		d.v |= uint32(d.buf[d.off])
+		d.off++
+		d.nbits += 8
+	}
+	d.nbits -= n
+	rv := d.v >> d.nbits
+	d.v &^= rv << d.nbits
+	return rv, true
+}
+
+// flushBits discards the unread bits in the buffer used by readBits.
+// It is used at the end of a line.
+func (d *decoder) flushBits() {
+	d.v = 0
+	d.nbits = 0
+}
+
+// minInt returns the smaller of x or y.
+func minInt(a, b int) int {
+	if a <= b {
+		return a
+	}
+	return b
+}
+
+// decode decodes the raw data of an image.
+// It reads from d.buf and writes the strip or tile into dst.
+func (d *decoder) decode(dst image.Image, xmin, ymin, xmax, ymax int) error {
+	d.off = 0
+
+	// Apply horizontal predictor if necessary.
+	// In this case, p contains the color difference to the preceding pixel.
+	// See page 64-65 of the spec.
+	if d.firstVal(tPredictor) == prHorizontal {
+		switch d.bpp {
+		case 16:
+			var off int
+			n := 2 * len(d.features[tBitsPerSample]) // bytes per sample times samples per pixel
+			for y := ymin; y < ymax; y++ {
+				off += n
+				for x := 0; x < (xmax-xmin-1)*n; x += 2 {
+					if off+2 > len(d.buf) {
+						return errNoPixels
+					}
+					v0 := d.byteOrder.Uint16(d.buf[off-n : off-n+2])
+					v1 := d.byteOrder.Uint16(d.buf[off : off+2])
+					d.byteOrder.PutUint16(d.buf[off:off+2], v1+v0)
+					off += 2
+				}
+			}
+		case 8:
+			var off int
+			n := 1 * len(d.features[tBitsPerSample]) // bytes per sample times samples per pixel
+			for y := ymin; y < ymax; y++ {
+				off += n
+				for x := 0; x < (xmax-xmin-1)*n; x++ {
+					if off >= len(d.buf) {
+						return errNoPixels
+					}
+					d.buf[off] += d.buf[off-n]
+					off++
+				}
+			}
+		case 1:
+			return UnsupportedError("horizontal predictor with 1 BitsPerSample")
+		}
+	}
+
+	rMaxX := minInt(xmax, dst.Bounds().Max.X)
+	rMaxY := minInt(ymax, dst.Bounds().Max.Y)
+	switch d.mode {
+	case mGray, mGrayInvert:
+		if d.bpp == 16 {
+			img := dst.(*image.Gray16)
+			for y := ymin; y < rMaxY; y++ {
+				for x := xmin; x < rMaxX; x++ {
+					if d.off+2 > len(d.buf) {
+						return errNoPixels
+					}
+					v := d.byteOrder.Uint16(d.buf[d.off : d.off+2])
+					d.off += 2
+					if d.mode == mGrayInvert {
+						v = 0xffff - v
+					}
+					img.SetGray16(x, y, color.Gray16{v})
+				}
+			}
+		} else {
+			img := dst.(*image.Gray)
+			max := uint32((1 << d.bpp) - 1)
+			for y := ymin; y < rMaxY; y++ {
+				for x := xmin; x < rMaxX; x++ {
+					v, ok := d.readBits(d.bpp)
+					if !ok {
+						return errNoPixels
+					}
+					v = v * 0xff / max
+					if d.mode == mGrayInvert {
+						v = 0xff - v
+					}
+					img.SetGray(x, y, color.Gray{uint8(v)})
+				}
+				d.flushBits()
+			}
+		}
+	case mPaletted:
+		img := dst.(*image.Paletted)
+		for y := ymin; y < rMaxY; y++ {
+			for x := xmin; x < rMaxX; x++ {
+				v, ok := d.readBits(d.bpp)
+				if !ok {
+					return errNoPixels
+				}
+				img.SetColorIndex(x, y, uint8(v))
+			}
+			d.flushBits()
+		}
+	case mRGB:
+		if d.bpp == 16 {
+			img := dst.(*image.RGBA64)
+			for y := ymin; y < rMaxY; y++ {
+				for x := xmin; x < rMaxX; x++ {
+					if d.off+6 > len(d.buf) {
+						return errNoPixels
+					}
+					r := d.byteOrder.Uint16(d.buf[d.off+0 : d.off+2])
+					g := d.byteOrder.Uint16(d.buf[d.off+2 : d.off+4])
+					b := d.byteOrder.Uint16(d.buf[d.off+4 : d.off+6])
+					d.off += 6
+					img.SetRGBA64(x, y, color.RGBA64{r, g, b, 0xffff})
+				}
+			}
+		} else {
+			img := dst.(*image.RGBA)
+			for y := ymin; y < rMaxY; y++ {
+				min := img.PixOffset(xmin, y)
+				max := img.PixOffset(rMaxX, y)
+				off := (y - ymin) * (xmax - xmin) * 3
+				for i := min; i < max; i += 4 {
+					if off+3 > len(d.buf) {
+						return errNoPixels
+					}
+					img.Pix[i+0] = d.buf[off+0]
+					img.Pix[i+1] = d.buf[off+1]
+					img.Pix[i+2] = d.buf[off+2]
+					img.Pix[i+3] = 0xff
+					off += 3
+				}
+			}
+		}
+	case mNRGBA:
+		if d.bpp == 16 {
+			img := dst.(*image.NRGBA64)
+			for y := ymin; y < rMaxY; y++ {
+				for x := xmin; x < rMaxX; x++ {
+					if d.off+8 > len(d.buf) {
+						return errNoPixels
+					}
+					r := d.byteOrder.Uint16(d.buf[d.off+0 : d.off+2])
+					g := d.byteOrder.Uint16(d.buf[d.off+2 : d.off+4])
+					b := d.byteOrder.Uint16(d.buf[d.off+4 : d.off+6])
+					a := d.byteOrder.Uint16(d.buf[d.off+6 : d.off+8])
+					d.off += 8
+					img.SetNRGBA64(x, y, color.NRGBA64{r, g, b, a})
+				}
+			}
+		} else {
+			img := dst.(*image.NRGBA)
+			for y := ymin; y < rMaxY; y++ {
+				min := img.PixOffset(xmin, y)
+				max := img.PixOffset(rMaxX, y)
+				i0, i1 := (y-ymin)*(xmax-xmin)*4, (y-ymin+1)*(xmax-xmin)*4
+				if i1 > len(d.buf) {
+					return errNoPixels
+				}
+				copy(img.Pix[min:max], d.buf[i0:i1])
+			}
+		}
+	case mRGBA:
+		if d.bpp == 16 {
+			img := dst.(*image.RGBA64)
+			for y := ymin; y < rMaxY; y++ {
+				for x := xmin; x < rMaxX; x++ {
+					if d.off+8 > len(d.buf) {
+						return errNoPixels
+					}
+					r := d.byteOrder.Uint16(d.buf[d.off+0 : d.off+2])
+					g := d.byteOrder.Uint16(d.buf[d.off+2 : d.off+4])
+					b := d.byteOrder.Uint16(d.buf[d.off+4 : d.off+6])
+					a := d.byteOrder.Uint16(d.buf[d.off+6 : d.off+8])
+					d.off += 8
+					img.SetRGBA64(x, y, color.RGBA64{r, g, b, a})
+				}
+			}
+		} else {
+			img := dst.(*image.RGBA)
+			for y := ymin; y < rMaxY; y++ {
+				min := img.PixOffset(xmin, y)
+				max := img.PixOffset(rMaxX, y)
+				i0, i1 := (y-ymin)*(xmax-xmin)*4, (y-ymin+1)*(xmax-xmin)*4
+				if i1 > len(d.buf) {
+					return errNoPixels
+				}
+				copy(img.Pix[min:max], d.buf[i0:i1])
+			}
+		}
+	}
+
+	return nil
+}
+
+func newDecoder(r io.Reader) (*decoder, error) {
+	d := &decoder{
+		r:        newReaderAt(r),
+		features: make(map[int][]uint),
+	}
+
+	p := make([]byte, 8)
+	if _, err := d.r.ReadAt(p, 0); err != nil {
+		return nil, err
+	}
+	switch string(p[0:4]) {
+	case leHeader:
+		d.byteOrder = binary.LittleEndian
+	case beHeader:
+		d.byteOrder = binary.BigEndian
+	default:
+		return nil, FormatError("malformed header")
+	}
+
+	ifdOffset := int64(d.byteOrder.Uint32(p[4:8]))
+
+	// The first two bytes contain the number of entries (12 bytes each).
+	if _, err := d.r.ReadAt(p[0:2], ifdOffset); err != nil {
+		return nil, err
+	}
+	numItems := int(d.byteOrder.Uint16(p[0:2]))
+
+	// All IFD entries are read in one chunk.
+	p = make([]byte, ifdLen*numItems)
+	if _, err := d.r.ReadAt(p, ifdOffset+2); err != nil {
+		return nil, err
+	}
+
+	for i := 0; i < len(p); i += ifdLen {
+		if err := d.parseIFD(p[i : i+ifdLen]); err != nil {
+			return nil, err
+		}
+	}
+
+	d.config.Width = int(d.firstVal(tImageWidth))
+	d.config.Height = int(d.firstVal(tImageLength))
+
+	if _, ok := d.features[tBitsPerSample]; !ok {
+		return nil, FormatError("BitsPerSample tag missing")
+	}
+	d.bpp = d.firstVal(tBitsPerSample)
+	switch d.bpp {
+	case 0:
+		return nil, FormatError("BitsPerSample must not be 0")
+	case 1, 8, 16:
+		// Nothing to do, these are accepted by this implementation.
+	default:
+		return nil, UnsupportedError(fmt.Sprintf("BitsPerSample of %v", d.bpp))
+	}
+
+	// Determine the image mode.
+	switch d.firstVal(tPhotometricInterpretation) {
+	case pRGB:
+		if d.bpp == 16 {
+			for _, b := range d.features[tBitsPerSample] {
+				if b != 16 {
+					return nil, FormatError("wrong number of samples for 16bit RGB")
+				}
+			}
+		} else {
+			for _, b := range d.features[tBitsPerSample] {
+				if b != 8 {
+					return nil, FormatError("wrong number of samples for 8bit RGB")
+				}
+			}
+		}
+		// RGB images normally have 3 samples per pixel.
+		// If there are more, ExtraSamples (p. 31-32 of the spec)
+		// gives their meaning (usually an alpha channel).
+		//
+		// This implementation does not support extra samples
+		// of an unspecified type.
+		switch len(d.features[tBitsPerSample]) {
+		case 3:
+			d.mode = mRGB
+			if d.bpp == 16 {
+				d.config.ColorModel = color.RGBA64Model
+			} else {
+				d.config.ColorModel = color.RGBAModel
+			}
+		case 4:
+			switch d.firstVal(tExtraSamples) {
+			case 1:
+				d.mode = mRGBA
+				if d.bpp == 16 {
+					d.config.ColorModel = color.RGBA64Model
+				} else {
+					d.config.ColorModel = color.RGBAModel
+				}
+			case 2:
+				d.mode = mNRGBA
+				if d.bpp == 16 {
+					d.config.ColorModel = color.NRGBA64Model
+				} else {
+					d.config.ColorModel = color.NRGBAModel
+				}
+			default:
+				return nil, FormatError("wrong number of samples for RGB")
+			}
+		default:
+			return nil, FormatError("wrong number of samples for RGB")
+		}
+	case pPaletted:
+		d.mode = mPaletted
+		d.config.ColorModel = color.Palette(d.palette)
+	case pWhiteIsZero:
+		d.mode = mGrayInvert
+		if d.bpp == 16 {
+			d.config.ColorModel = color.Gray16Model
+		} else {
+			d.config.ColorModel = color.GrayModel
+		}
+	case pBlackIsZero:
+		d.mode = mGray
+		if d.bpp == 16 {
+			d.config.ColorModel = color.Gray16Model
+		} else {
+			d.config.ColorModel = color.GrayModel
+		}
+	default:
+		return nil, UnsupportedError("color model")
+	}
+
+	return d, nil
+}
+
+// DecodeConfig returns the color model and dimensions of a TIFF image without
+// decoding the entire image.
+func DecodeConfig(r io.Reader) (image.Config, error) {
+	d, err := newDecoder(r)
+	if err != nil {
+		return image.Config{}, err
+	}
+	return d.config, nil
+}
+
+// Decode reads a TIFF image from r and returns it as an image.Image.
+// The type of Image returned depends on the contents of the TIFF.
+func Decode(r io.Reader) (img image.Image, err error) {
+	d, err := newDecoder(r)
+	if err != nil {
+		return
+	}
+
+	blockPadding := false
+	blockWidth := d.config.Width
+	blockHeight := d.config.Height
+	blocksAcross := 1
+	blocksDown := 1
+
+	if d.config.Width == 0 {
+		blocksAcross = 0
+	}
+	if d.config.Height == 0 {
+		blocksDown = 0
+	}
+
+	var blockOffsets, blockCounts []uint
+
+	if int(d.firstVal(tTileWidth)) != 0 {
+		blockPadding = true
+
+		blockWidth = int(d.firstVal(tTileWidth))
+		blockHeight = int(d.firstVal(tTileLength))
+
+		if blockWidth != 0 {
+			blocksAcross = (d.config.Width + blockWidth - 1) / blockWidth
+		}
+		if blockHeight != 0 {
+			blocksDown = (d.config.Height + blockHeight - 1) / blockHeight
+		}
+
+		blockCounts = d.features[tTileByteCounts]
+		blockOffsets = d.features[tTileOffsets]
+
+	} else {
+		if int(d.firstVal(tRowsPerStrip)) != 0 {
+			blockHeight = int(d.firstVal(tRowsPerStrip))
+		}
+
+		if blockHeight != 0 {
+			blocksDown = (d.config.Height + blockHeight - 1) / blockHeight
+		}
+
+		blockOffsets = d.features[tStripOffsets]
+		blockCounts = d.features[tStripByteCounts]
+	}
+
+	// Check if we have the right number of strips/tiles, offsets and counts.
+	if n := blocksAcross * blocksDown; len(blockOffsets) < n || len(blockCounts) < n {
+		return nil, FormatError("inconsistent header")
+	}
+
+	imgRect := image.Rect(0, 0, d.config.Width, d.config.Height)
+	switch d.mode {
+	case mGray, mGrayInvert:
+		if d.bpp == 16 {
+			img = image.NewGray16(imgRect)
+		} else {
+			img = image.NewGray(imgRect)
+		}
+	case mPaletted:
+		img = image.NewPaletted(imgRect, d.palette)
+	case mNRGBA:
+		if d.bpp == 16 {
+			img = image.NewNRGBA64(imgRect)
+		} else {
+			img = image.NewNRGBA(imgRect)
+		}
+	case mRGB, mRGBA:
+		if d.bpp == 16 {
+			img = image.NewRGBA64(imgRect)
+		} else {
+			img = image.NewRGBA(imgRect)
+		}
+	}
+
+	for i := 0; i < blocksAcross; i++ {
+		blkW := blockWidth
+		if !blockPadding && i == blocksAcross-1 && d.config.Width%blockWidth != 0 {
+			blkW = d.config.Width % blockWidth
+		}
+		for j := 0; j < blocksDown; j++ {
+			blkH := blockHeight
+			if !blockPadding && j == blocksDown-1 && d.config.Height%blockHeight != 0 {
+				blkH = d.config.Height % blockHeight
+			}
+			offset := int64(blockOffsets[j*blocksAcross+i])
+			n := int64(blockCounts[j*blocksAcross+i])
+			switch d.firstVal(tCompression) {
+
+			// According to the spec, Compression does not have a default value,
+			// but some tools interpret a missing Compression value as none so we do
+			// the same.
+			case cNone, 0:
+				if b, ok := d.r.(*buffer); ok {
+					d.buf, err = b.Slice(int(offset), int(n))
+				} else {
+					d.buf = make([]byte, n)
+					_, err = d.r.ReadAt(d.buf, offset)
+				}
+			case cLZW:
+				r := lzw.NewReader(io.NewSectionReader(d.r, offset, n), lzw.MSB, 8)
+				d.buf, err = ioutil.ReadAll(r)
+				r.Close()
+			case cDeflate, cDeflateOld:
+				var r io.ReadCloser
+				r, err = zlib.NewReader(io.NewSectionReader(d.r, offset, n))
+				if err != nil {
+					return nil, err
+				}
+				d.buf, err = ioutil.ReadAll(r)
+				r.Close()
+			case cPackBits:
+				d.buf, err = unpackBits(io.NewSectionReader(d.r, offset, n))
+			default:
+				err = UnsupportedError(fmt.Sprintf("compression value %d", d.firstVal(tCompression)))
+			}
+			if err != nil {
+				return nil, err
+			}
+
+			xmin := i * blockWidth
+			ymin := j * blockHeight
+			xmax := xmin + blkW
+			ymax := ymin + blkH
+			err = d.decode(img, xmin, ymin, xmax, ymax)
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+	return
+}
+
+func init() {
+	image.RegisterFormat("tiff", leHeader, Decode, DecodeConfig)
+	image.RegisterFormat("tiff", beHeader, Decode, DecodeConfig)
+}
diff --git a/vendor/golang.org/x/image/tiff/writer.go b/vendor/golang.org/x/image/tiff/writer.go
new file mode 100644
index 000000000..c8a01cea7
--- /dev/null
+++ b/vendor/golang.org/x/image/tiff/writer.go
@@ -0,0 +1,438 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tiff
+
+import (
+	"bytes"
+	"compress/zlib"
+	"encoding/binary"
+	"image"
+	"io"
+	"sort"
+)
+
+// The TIFF format allows to choose the order of the different elements freely.
+// The basic structure of a TIFF file written by this package is:
+//
+//   1. Header (8 bytes).
+//   2. Image data.
+//   3. Image File Directory (IFD).
+//   4. "Pointer area" for larger entries in the IFD.
+
+// We only write little-endian TIFF files.
+var enc = binary.LittleEndian
+
+// An ifdEntry is a single entry in an Image File Directory.
+// A value of type dtRational is composed of two 32-bit values,
+// thus data contains two uints (numerator and denominator) for a single number.
+type ifdEntry struct {
+	tag      int
+	datatype int
+	data     []uint32
+}
+
+func (e ifdEntry) putData(p []byte) {
+	for _, d := range e.data {
+		switch e.datatype {
+		case dtByte, dtASCII:
+			p[0] = byte(d)
+			p = p[1:]
+		case dtShort:
+			enc.PutUint16(p, uint16(d))
+			p = p[2:]
+		case dtLong, dtRational:
+			enc.PutUint32(p, uint32(d))
+			p = p[4:]
+		}
+	}
+}
+
+type byTag []ifdEntry
+
+func (d byTag) Len() int           { return len(d) }
+func (d byTag) Less(i, j int) bool { return d[i].tag < d[j].tag }
+func (d byTag) Swap(i, j int)      { d[i], d[j] = d[j], d[i] }
+
+func encodeGray(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
+	if !predictor {
+		return writePix(w, pix, dy, dx, stride)
+	}
+	buf := make([]byte, dx)
+	for y := 0; y < dy; y++ {
+		min := y*stride + 0
+		max := y*stride + dx
+		off := 0
+		var v0 uint8
+		for i := min; i < max; i++ {
+			v1 := pix[i]
+			buf[off] = v1 - v0
+			v0 = v1
+			off++
+		}
+		if _, err := w.Write(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func encodeGray16(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
+	buf := make([]byte, dx*2)
+	for y := 0; y < dy; y++ {
+		min := y*stride + 0
+		max := y*stride + dx*2
+		off := 0
+		var v0 uint16
+		for i := min; i < max; i += 2 {
+			// An image.Gray16's Pix is in big-endian order.
+			v1 := uint16(pix[i])<<8 | uint16(pix[i+1])
+			if predictor {
+				v0, v1 = v1, v1-v0
+			}
+			// We only write little-endian TIFF files.
+			buf[off+0] = byte(v1)
+			buf[off+1] = byte(v1 >> 8)
+			off += 2
+		}
+		if _, err := w.Write(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func encodeRGBA(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
+	if !predictor {
+		return writePix(w, pix, dy, dx*4, stride)
+	}
+	buf := make([]byte, dx*4)
+	for y := 0; y < dy; y++ {
+		min := y*stride + 0
+		max := y*stride + dx*4
+		off := 0
+		var r0, g0, b0, a0 uint8
+		for i := min; i < max; i += 4 {
+			r1, g1, b1, a1 := pix[i+0], pix[i+1], pix[i+2], pix[i+3]
+			buf[off+0] = r1 - r0
+			buf[off+1] = g1 - g0
+			buf[off+2] = b1 - b0
+			buf[off+3] = a1 - a0
+			off += 4
+			r0, g0, b0, a0 = r1, g1, b1, a1
+		}
+		if _, err := w.Write(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func encodeRGBA64(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
+	buf := make([]byte, dx*8)
+	for y := 0; y < dy; y++ {
+		min := y*stride + 0
+		max := y*stride + dx*8
+		off := 0
+		var r0, g0, b0, a0 uint16
+		for i := min; i < max; i += 8 {
+			// An image.RGBA64's Pix is in big-endian order.
+			r1 := uint16(pix[i+0])<<8 | uint16(pix[i+1])
+			g1 := uint16(pix[i+2])<<8 | uint16(pix[i+3])
+			b1 := uint16(pix[i+4])<<8 | uint16(pix[i+5])
+			a1 := uint16(pix[i+6])<<8 | uint16(pix[i+7])
+			if predictor {
+				r0, r1 = r1, r1-r0
+				g0, g1 = g1, g1-g0
+				b0, b1 = b1, b1-b0
+				a0, a1 = a1, a1-a0
+			}
+			// We only write little-endian TIFF files.
+			buf[off+0] = byte(r1)
+			buf[off+1] = byte(r1 >> 8)
+			buf[off+2] = byte(g1)
+			buf[off+3] = byte(g1 >> 8)
+			buf[off+4] = byte(b1)
+			buf[off+5] = byte(b1 >> 8)
+			buf[off+6] = byte(a1)
+			buf[off+7] = byte(a1 >> 8)
+			off += 8
+		}
+		if _, err := w.Write(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func encode(w io.Writer, m image.Image, predictor bool) error {
+	bounds := m.Bounds()
+	buf := make([]byte, 4*bounds.Dx())
+	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+		off := 0
+		if predictor {
+			var r0, g0, b0, a0 uint8
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				r, g, b, a := m.At(x, y).RGBA()
+				r1 := uint8(r >> 8)
+				g1 := uint8(g >> 8)
+				b1 := uint8(b >> 8)
+				a1 := uint8(a >> 8)
+				buf[off+0] = r1 - r0
+				buf[off+1] = g1 - g0
+				buf[off+2] = b1 - b0
+				buf[off+3] = a1 - a0
+				off += 4
+				r0, g0, b0, a0 = r1, g1, b1, a1
+			}
+		} else {
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				r, g, b, a := m.At(x, y).RGBA()
+				buf[off+0] = uint8(r >> 8)
+				buf[off+1] = uint8(g >> 8)
+				buf[off+2] = uint8(b >> 8)
+				buf[off+3] = uint8(a >> 8)
+				off += 4
+			}
+		}
+		if _, err := w.Write(buf); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// writePix writes the internal byte array of an image to w. It is less general
+// but much faster then encode. writePix is used when pix directly
+// corresponds to one of the TIFF image types.
+func writePix(w io.Writer, pix []byte, nrows, length, stride int) error {
+	if length == stride {
+		_, err := w.Write(pix[:nrows*length])
+		return err
+	}
+	for ; nrows > 0; nrows-- {
+		if _, err := w.Write(pix[:length]); err != nil {
+			return err
+		}
+		pix = pix[stride:]
+	}
+	return nil
+}
+
+func writeIFD(w io.Writer, ifdOffset int, d []ifdEntry) error {
+	var buf [ifdLen]byte
+	// Make space for "pointer area" containing IFD entry data
+	// longer than 4 bytes.
+	parea := make([]byte, 1024)
+	pstart := ifdOffset + ifdLen*len(d) + 6
+	var o int // Current offset in parea.
+
+	// The IFD has to be written with the tags in ascending order.
+	sort.Sort(byTag(d))
+
+	// Write the number of entries in this IFD.
+	if err := binary.Write(w, enc, uint16(len(d))); err != nil {
+		return err
+	}
+	for _, ent := range d {
+		enc.PutUint16(buf[0:2], uint16(ent.tag))
+		enc.PutUint16(buf[2:4], uint16(ent.datatype))
+		count := uint32(len(ent.data))
+		if ent.datatype == dtRational {
+			count /= 2
+		}
+		enc.PutUint32(buf[4:8], count)
+		datalen := int(count * lengths[ent.datatype])
+		if datalen <= 4 {
+			ent.putData(buf[8:12])
+		} else {
+			if (o + datalen) > len(parea) {
+				newlen := len(parea) + 1024
+				for (o + datalen) > newlen {
+					newlen += 1024
+				}
+				newarea := make([]byte, newlen)
+				copy(newarea, parea)
+				parea = newarea
+			}
+			ent.putData(parea[o : o+datalen])
+			enc.PutUint32(buf[8:12], uint32(pstart+o))
+			o += datalen
+		}
+		if _, err := w.Write(buf[:]); err != nil {
+			return err
+		}
+	}
+	// The IFD ends with the offset of the next IFD in the file,
+	// or zero if it is the last one (page 14).
+	if err := binary.Write(w, enc, uint32(0)); err != nil {
+		return err
+	}
+	_, err := w.Write(parea[:o])
+	return err
+}
+
+// Options are the encoding parameters.
+type Options struct {
+	// Compression is the type of compression used.
+	Compression CompressionType
+	// Predictor determines whether a differencing predictor is used;
+	// if true, instead of each pixel's color, the color difference to the
+	// preceding one is saved.  This improves the compression for certain
+	// types of images and compressors. For example, it works well for
+	// photos with Deflate compression.
+	Predictor bool
+}
+
+// Encode writes the image m to w. opt determines the options used for
+// encoding, such as the compression type. If opt is nil, an uncompressed
+// image is written.
+func Encode(w io.Writer, m image.Image, opt *Options) error {
+	d := m.Bounds().Size()
+
+	compression := uint32(cNone)
+	predictor := false
+	if opt != nil {
+		compression = opt.Compression.specValue()
+		// The predictor field is only used with LZW. See page 64 of the spec.
+		predictor = opt.Predictor && compression == cLZW
+	}
+
+	_, err := io.WriteString(w, leHeader)
+	if err != nil {
+		return err
+	}
+
+	// Compressed data is written into a buffer first, so that we
+	// know the compressed size.
+	var buf bytes.Buffer
+	// dst holds the destination for the pixel data of the image --
+	// either w or a writer to buf.
+	var dst io.Writer
+	// imageLen is the length of the pixel data in bytes.
+	// The offset of the IFD is imageLen + 8 header bytes.
+	var imageLen int
+
+	switch compression {
+	case cNone:
+		dst = w
+		// Write IFD offset before outputting pixel data.
+		switch m.(type) {
+		case *image.Paletted:
+			imageLen = d.X * d.Y * 1
+		case *image.Gray:
+			imageLen = d.X * d.Y * 1
+		case *image.Gray16:
+			imageLen = d.X * d.Y * 2
+		case *image.RGBA64:
+			imageLen = d.X * d.Y * 8
+		case *image.NRGBA64:
+			imageLen = d.X * d.Y * 8
+		default:
+			imageLen = d.X * d.Y * 4
+		}
+		err = binary.Write(w, enc, uint32(imageLen+8))
+		if err != nil {
+			return err
+		}
+	case cDeflate:
+		dst = zlib.NewWriter(&buf)
+	}
+
+	pr := uint32(prNone)
+	photometricInterpretation := uint32(pRGB)
+	samplesPerPixel := uint32(4)
+	bitsPerSample := []uint32{8, 8, 8, 8}
+	extraSamples := uint32(0)
+	colorMap := []uint32{}
+
+	if predictor {
+		pr = prHorizontal
+	}
+	switch m := m.(type) {
+	case *image.Paletted:
+		photometricInterpretation = pPaletted
+		samplesPerPixel = 1
+		bitsPerSample = []uint32{8}
+		colorMap = make([]uint32, 256*3)
+		for i := 0; i < 256 && i < len(m.Palette); i++ {
+			r, g, b, _ := m.Palette[i].RGBA()
+			colorMap[i+0*256] = uint32(r)
+			colorMap[i+1*256] = uint32(g)
+			colorMap[i+2*256] = uint32(b)
+		}
+		err = encodeGray(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
+	case *image.Gray:
+		photometricInterpretation = pBlackIsZero
+		samplesPerPixel = 1
+		bitsPerSample = []uint32{8}
+		err = encodeGray(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
+	case *image.Gray16:
+		photometricInterpretation = pBlackIsZero
+		samplesPerPixel = 1
+		bitsPerSample = []uint32{16}
+		err = encodeGray16(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
+	case *image.NRGBA:
+		extraSamples = 2 // Unassociated alpha.
+		err = encodeRGBA(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
+	case *image.NRGBA64:
+		extraSamples = 2 // Unassociated alpha.
+		bitsPerSample = []uint32{16, 16, 16, 16}
+		err = encodeRGBA64(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
+	case *image.RGBA:
+		extraSamples = 1 // Associated alpha.
+		err = encodeRGBA(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
+	case *image.RGBA64:
+		extraSamples = 1 // Associated alpha.
+		bitsPerSample = []uint32{16, 16, 16, 16}
+		err = encodeRGBA64(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
+	default:
+		extraSamples = 1 // Associated alpha.
+		err = encode(dst, m, predictor)
+	}
+	if err != nil {
+		return err
+	}
+
+	if compression != cNone {
+		if err = dst.(io.Closer).Close(); err != nil {
+			return err
+		}
+		imageLen = buf.Len()
+		if err = binary.Write(w, enc, uint32(imageLen+8)); err != nil {
+			return err
+		}
+		if _, err = buf.WriteTo(w); err != nil {
+			return err
+		}
+	}
+
+	ifd := []ifdEntry{
+		{tImageWidth, dtShort, []uint32{uint32(d.X)}},
+		{tImageLength, dtShort, []uint32{uint32(d.Y)}},
+		{tBitsPerSample, dtShort, bitsPerSample},
+		{tCompression, dtShort, []uint32{compression}},
+		{tPhotometricInterpretation, dtShort, []uint32{photometricInterpretation}},
+		{tStripOffsets, dtLong, []uint32{8}},
+		{tSamplesPerPixel, dtShort, []uint32{samplesPerPixel}},
+		{tRowsPerStrip, dtShort, []uint32{uint32(d.Y)}},
+		{tStripByteCounts, dtLong, []uint32{uint32(imageLen)}},
+		// There is currently no support for storing the image
+		// resolution, so give a bogus value of 72x72 dpi.
+		{tXResolution, dtRational, []uint32{72, 1}},
+		{tYResolution, dtRational, []uint32{72, 1}},
+		{tResolutionUnit, dtShort, []uint32{resPerInch}},
+	}
+	if pr != prNone {
+		ifd = append(ifd, ifdEntry{tPredictor, dtShort, []uint32{pr}})
+	}
+	if len(colorMap) != 0 {
+		ifd = append(ifd, ifdEntry{tColorMap, dtShort, colorMap})
+	}
+	if extraSamples > 0 {
+		ifd = append(ifd, ifdEntry{tExtraSamples, dtShort, []uint32{extraSamples}})
+	}
+
+	return writeIFD(w, imageLen+8, ifd)
+}