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// Copyright 2012 The Graphics-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 interp
import (
"image"
"image/color"
"math"
)
// Bilinear implements bilinear interpolation.
var Bilinear Interp = bilinear{}
type bilinear struct{}
func (i bilinear) Interp(src image.Image, x, y float64) color.Color {
if src, ok := src.(*image.RGBA); ok {
return i.RGBA(src, x, y)
}
return bilinearGeneral(src, x, y)
}
func bilinearGeneral(src image.Image, x, y float64) color.Color {
p := findLinearSrc(src.Bounds(), x, y)
var fr, fg, fb, fa float64
var r, g, b, a uint32
r, g, b, a = src.At(p.low.X, p.low.Y).RGBA()
fr += float64(r) * p.frac00
fg += float64(g) * p.frac00
fb += float64(b) * p.frac00
fa += float64(a) * p.frac00
r, g, b, a = src.At(p.high.X, p.low.Y).RGBA()
fr += float64(r) * p.frac01
fg += float64(g) * p.frac01
fb += float64(b) * p.frac01
fa += float64(a) * p.frac01
r, g, b, a = src.At(p.low.X, p.high.Y).RGBA()
fr += float64(r) * p.frac10
fg += float64(g) * p.frac10
fb += float64(b) * p.frac10
fa += float64(a) * p.frac10
r, g, b, a = src.At(p.high.X, p.high.Y).RGBA()
fr += float64(r) * p.frac11
fg += float64(g) * p.frac11
fb += float64(b) * p.frac11
fa += float64(a) * p.frac11
var c color.RGBA64
c.R = uint16(fr + 0.5)
c.G = uint16(fg + 0.5)
c.B = uint16(fb + 0.5)
c.A = uint16(fa + 0.5)
return c
}
func (bilinear) RGBA(src *image.RGBA, x, y float64) color.RGBA {
p := findLinearSrc(src.Bounds(), x, y)
// Array offsets for the surrounding pixels.
off00 := offRGBA(src, p.low.X, p.low.Y)
off01 := offRGBA(src, p.high.X, p.low.Y)
off10 := offRGBA(src, p.low.X, p.high.Y)
off11 := offRGBA(src, p.high.X, p.high.Y)
var fr, fg, fb, fa float64
fr += float64(src.Pix[off00+0]) * p.frac00
fg += float64(src.Pix[off00+1]) * p.frac00
fb += float64(src.Pix[off00+2]) * p.frac00
fa += float64(src.Pix[off00+3]) * p.frac00
fr += float64(src.Pix[off01+0]) * p.frac01
fg += float64(src.Pix[off01+1]) * p.frac01
fb += float64(src.Pix[off01+2]) * p.frac01
fa += float64(src.Pix[off01+3]) * p.frac01
fr += float64(src.Pix[off10+0]) * p.frac10
fg += float64(src.Pix[off10+1]) * p.frac10
fb += float64(src.Pix[off10+2]) * p.frac10
fa += float64(src.Pix[off10+3]) * p.frac10
fr += float64(src.Pix[off11+0]) * p.frac11
fg += float64(src.Pix[off11+1]) * p.frac11
fb += float64(src.Pix[off11+2]) * p.frac11
fa += float64(src.Pix[off11+3]) * p.frac11
var c color.RGBA
c.R = uint8(fr + 0.5)
c.G = uint8(fg + 0.5)
c.B = uint8(fb + 0.5)
c.A = uint8(fa + 0.5)
return c
}
func (bilinear) Gray(src *image.Gray, x, y float64) color.Gray {
p := findLinearSrc(src.Bounds(), x, y)
// Array offsets for the surrounding pixels.
off00 := offGray(src, p.low.X, p.low.Y)
off01 := offGray(src, p.high.X, p.low.Y)
off10 := offGray(src, p.low.X, p.high.Y)
off11 := offGray(src, p.high.X, p.high.Y)
var fc float64
fc += float64(src.Pix[off00]) * p.frac00
fc += float64(src.Pix[off01]) * p.frac01
fc += float64(src.Pix[off10]) * p.frac10
fc += float64(src.Pix[off11]) * p.frac11
var c color.Gray
c.Y = uint8(fc + 0.5)
return c
}
type bilinearSrc struct {
// Top-left and bottom-right interpolation sources
low, high image.Point
// Fraction of each pixel to take. The 0 suffix indicates
// top/left, and the 1 suffix indicates bottom/right.
frac00, frac01, frac10, frac11 float64
}
func findLinearSrc(b image.Rectangle, sx, sy float64) bilinearSrc {
maxX := float64(b.Max.X)
maxY := float64(b.Max.Y)
minX := float64(b.Min.X)
minY := float64(b.Min.Y)
lowX := math.Floor(sx - 0.5)
lowY := math.Floor(sy - 0.5)
if lowX < minX {
lowX = minX
}
if lowY < minY {
lowY = minY
}
highX := math.Ceil(sx - 0.5)
highY := math.Ceil(sy - 0.5)
if highX >= maxX {
highX = maxX - 1
}
if highY >= maxY {
highY = maxY - 1
}
// In the variables below, the 0 suffix indicates top/left, and the
// 1 suffix indicates bottom/right.
// Center of each surrounding pixel.
x00 := lowX + 0.5
y00 := lowY + 0.5
x01 := highX + 0.5
y01 := lowY + 0.5
x10 := lowX + 0.5
y10 := highY + 0.5
x11 := highX + 0.5
y11 := highY + 0.5
p := bilinearSrc{
low: image.Pt(int(lowX), int(lowY)),
high: image.Pt(int(highX), int(highY)),
}
// Literally, edge cases. If we are close enough to the edge of
// the image, curtail the interpolation sources.
if lowX == highX && lowY == highY {
p.frac00 = 1.0
} else if sy-minY <= 0.5 && sx-minX <= 0.5 {
p.frac00 = 1.0
} else if maxY-sy <= 0.5 && maxX-sx <= 0.5 {
p.frac11 = 1.0
} else if sy-minY <= 0.5 || lowY == highY {
p.frac00 = x01 - sx
p.frac01 = sx - x00
} else if sx-minX <= 0.5 || lowX == highX {
p.frac00 = y10 - sy
p.frac10 = sy - y00
} else if maxY-sy <= 0.5 {
p.frac10 = x11 - sx
p.frac11 = sx - x10
} else if maxX-sx <= 0.5 {
p.frac01 = y11 - sy
p.frac11 = sy - y01
} else {
p.frac00 = (x01 - sx) * (y10 - sy)
p.frac01 = (sx - x00) * (y11 - sy)
p.frac10 = (x11 - sx) * (sy - y00)
p.frac11 = (sx - x10) * (sy - y01)
}
return p
}
// TODO(crawshaw): When we have inlining, consider func (p *RGBA) Off(x, y) int
func offRGBA(src *image.RGBA, x, y int) int {
return (y-src.Rect.Min.Y)*src.Stride + (x-src.Rect.Min.X)*4
}
func offGray(src *image.Gray, x, y int) int {
return (y-src.Rect.Min.Y)*src.Stride + (x - src.Rect.Min.X)
}
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