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Diffstat (limited to 'vendor/github.com/golang/freetype/raster/paint.go')
| -rw-r--r-- | vendor/github.com/golang/freetype/raster/paint.go | 287 |
1 files changed, 287 insertions, 0 deletions
diff --git a/vendor/github.com/golang/freetype/raster/paint.go b/vendor/github.com/golang/freetype/raster/paint.go new file mode 100644 index 000000000..652256cca --- /dev/null +++ b/vendor/github.com/golang/freetype/raster/paint.go @@ -0,0 +1,287 @@ +// Copyright 2010 The Freetype-Go Authors. All rights reserved. +// Use of this source code is governed by your choice of either the +// FreeType License or the GNU General Public License version 2 (or +// any later version), both of which can be found in the LICENSE file. + +package raster + +import ( + "image" + "image/color" + "image/draw" + "math" +) + +// A Span is a horizontal segment of pixels with constant alpha. X0 is an +// inclusive bound and X1 is exclusive, the same as for slices. A fully opaque +// Span has Alpha == 0xffff. +type Span struct { + Y, X0, X1 int + Alpha uint32 +} + +// A Painter knows how to paint a batch of Spans. Rasterization may involve +// Painting multiple batches, and done will be true for the final batch. The +// Spans' Y values are monotonically increasing during a rasterization. Paint +// may use all of ss as scratch space during the call. +type Painter interface { + Paint(ss []Span, done bool) +} + +// The PainterFunc type adapts an ordinary function to the Painter interface. +type PainterFunc func(ss []Span, done bool) + +// Paint just delegates the call to f. +func (f PainterFunc) Paint(ss []Span, done bool) { f(ss, done) } + +// An AlphaOverPainter is a Painter that paints Spans onto a *image.Alpha using +// the Over Porter-Duff composition operator. +type AlphaOverPainter struct { + Image *image.Alpha +} + +// Paint satisfies the Painter interface. +func (r AlphaOverPainter) Paint(ss []Span, done bool) { + b := r.Image.Bounds() + for _, s := range ss { + if s.Y < b.Min.Y { + continue + } + if s.Y >= b.Max.Y { + return + } + if s.X0 < b.Min.X { + s.X0 = b.Min.X + } + if s.X1 > b.Max.X { + s.X1 = b.Max.X + } + if s.X0 >= s.X1 { + continue + } + base := (s.Y-r.Image.Rect.Min.Y)*r.Image.Stride - r.Image.Rect.Min.X + p := r.Image.Pix[base+s.X0 : base+s.X1] + a := int(s.Alpha >> 8) + for i, c := range p { + v := int(c) + p[i] = uint8((v*255 + (255-v)*a) / 255) + } + } +} + +// NewAlphaOverPainter creates a new AlphaOverPainter for the given image. +func NewAlphaOverPainter(m *image.Alpha) AlphaOverPainter { + return AlphaOverPainter{m} +} + +// An AlphaSrcPainter is a Painter that paints Spans onto a *image.Alpha using +// the Src Porter-Duff composition operator. +type AlphaSrcPainter struct { + Image *image.Alpha +} + +// Paint satisfies the Painter interface. +func (r AlphaSrcPainter) Paint(ss []Span, done bool) { + b := r.Image.Bounds() + for _, s := range ss { + if s.Y < b.Min.Y { + continue + } + if s.Y >= b.Max.Y { + return + } + if s.X0 < b.Min.X { + s.X0 = b.Min.X + } + if s.X1 > b.Max.X { + s.X1 = b.Max.X + } + if s.X0 >= s.X1 { + continue + } + base := (s.Y-r.Image.Rect.Min.Y)*r.Image.Stride - r.Image.Rect.Min.X + p := r.Image.Pix[base+s.X0 : base+s.X1] + color := uint8(s.Alpha >> 8) + for i := range p { + p[i] = color + } + } +} + +// NewAlphaSrcPainter creates a new AlphaSrcPainter for the given image. +func NewAlphaSrcPainter(m *image.Alpha) AlphaSrcPainter { + return AlphaSrcPainter{m} +} + +// An RGBAPainter is a Painter that paints Spans onto a *image.RGBA. +type RGBAPainter struct { + // Image is the image to compose onto. + Image *image.RGBA + // Op is the Porter-Duff composition operator. + Op draw.Op + // cr, cg, cb and ca are the 16-bit color to paint the spans. + cr, cg, cb, ca uint32 +} + +// Paint satisfies the Painter interface. +func (r *RGBAPainter) Paint(ss []Span, done bool) { + b := r.Image.Bounds() + for _, s := range ss { + if s.Y < b.Min.Y { + continue + } + if s.Y >= b.Max.Y { + return + } + if s.X0 < b.Min.X { + s.X0 = b.Min.X + } + if s.X1 > b.Max.X { + s.X1 = b.Max.X + } + if s.X0 >= s.X1 { + continue + } + // This code mimics drawGlyphOver in $GOROOT/src/image/draw/draw.go. + ma := s.Alpha + const m = 1<<16 - 1 + i0 := (s.Y-r.Image.Rect.Min.Y)*r.Image.Stride + (s.X0-r.Image.Rect.Min.X)*4 + i1 := i0 + (s.X1-s.X0)*4 + if r.Op == draw.Over { + for i := i0; i < i1; i += 4 { + dr := uint32(r.Image.Pix[i+0]) + dg := uint32(r.Image.Pix[i+1]) + db := uint32(r.Image.Pix[i+2]) + da := uint32(r.Image.Pix[i+3]) + a := (m - (r.ca * ma / m)) * 0x101 + r.Image.Pix[i+0] = uint8((dr*a + r.cr*ma) / m >> 8) + r.Image.Pix[i+1] = uint8((dg*a + r.cg*ma) / m >> 8) + r.Image.Pix[i+2] = uint8((db*a + r.cb*ma) / m >> 8) + r.Image.Pix[i+3] = uint8((da*a + r.ca*ma) / m >> 8) + } + } else { + for i := i0; i < i1; i += 4 { + r.Image.Pix[i+0] = uint8(r.cr * ma / m >> 8) + r.Image.Pix[i+1] = uint8(r.cg * ma / m >> 8) + r.Image.Pix[i+2] = uint8(r.cb * ma / m >> 8) + r.Image.Pix[i+3] = uint8(r.ca * ma / m >> 8) + } + } + } +} + +// SetColor sets the color to paint the spans. +func (r *RGBAPainter) SetColor(c color.Color) { + r.cr, r.cg, r.cb, r.ca = c.RGBA() +} + +// NewRGBAPainter creates a new RGBAPainter for the given image. +func NewRGBAPainter(m *image.RGBA) *RGBAPainter { + return &RGBAPainter{Image: m} +} + +// A MonochromePainter wraps another Painter, quantizing each Span's alpha to +// be either fully opaque or fully transparent. +type MonochromePainter struct { + Painter Painter + y, x0, x1 int +} + +// Paint delegates to the wrapped Painter after quantizing each Span's alpha +// value and merging adjacent fully opaque Spans. +func (m *MonochromePainter) Paint(ss []Span, done bool) { + // We compact the ss slice, discarding any Spans whose alpha quantizes to zero. + j := 0 + for _, s := range ss { + if s.Alpha >= 0x8000 { + if m.y == s.Y && m.x1 == s.X0 { + m.x1 = s.X1 + } else { + ss[j] = Span{m.y, m.x0, m.x1, 1<<16 - 1} + j++ + m.y, m.x0, m.x1 = s.Y, s.X0, s.X1 + } + } + } + if done { + // Flush the accumulated Span. + finalSpan := Span{m.y, m.x0, m.x1, 1<<16 - 1} + if j < len(ss) { + ss[j] = finalSpan + j++ + m.Painter.Paint(ss[:j], true) + } else if j == len(ss) { + m.Painter.Paint(ss, false) + if cap(ss) > 0 { + ss = ss[:1] + } else { + ss = make([]Span, 1) + } + ss[0] = finalSpan + m.Painter.Paint(ss, true) + } else { + panic("unreachable") + } + // Reset the accumulator, so that this Painter can be re-used. + m.y, m.x0, m.x1 = 0, 0, 0 + } else { + m.Painter.Paint(ss[:j], false) + } +} + +// NewMonochromePainter creates a new MonochromePainter that wraps the given +// Painter. +func NewMonochromePainter(p Painter) *MonochromePainter { + return &MonochromePainter{Painter: p} +} + +// A GammaCorrectionPainter wraps another Painter, performing gamma-correction +// on each Span's alpha value. +type GammaCorrectionPainter struct { + // Painter is the wrapped Painter. + Painter Painter + // a is the precomputed alpha values for linear interpolation, with fully + // opaque == 0xffff. + a [256]uint16 + // gammaIsOne is whether gamma correction is a no-op. + gammaIsOne bool +} + +// Paint delegates to the wrapped Painter after performing gamma-correction on +// each Span. +func (g *GammaCorrectionPainter) Paint(ss []Span, done bool) { + if !g.gammaIsOne { + const n = 0x101 + for i, s := range ss { + if s.Alpha == 0 || s.Alpha == 0xffff { + continue + } + p, q := s.Alpha/n, s.Alpha%n + // The resultant alpha is a linear interpolation of g.a[p] and g.a[p+1]. + a := uint32(g.a[p])*(n-q) + uint32(g.a[p+1])*q + ss[i].Alpha = (a + n/2) / n + } + } + g.Painter.Paint(ss, done) +} + +// SetGamma sets the gamma value. +func (g *GammaCorrectionPainter) SetGamma(gamma float64) { + g.gammaIsOne = gamma == 1 + if g.gammaIsOne { + return + } + for i := 0; i < 256; i++ { + a := float64(i) / 0xff + a = math.Pow(a, gamma) + g.a[i] = uint16(0xffff * a) + } +} + +// NewGammaCorrectionPainter creates a new GammaCorrectionPainter that wraps +// the given Painter. +func NewGammaCorrectionPainter(p Painter, gamma float64) *GammaCorrectionPainter { + g := &GammaCorrectionPainter{Painter: p} + g.SetGamma(gamma) + return g +} |