/
bilinear.go
196 lines (166 loc) · 5.05 KB
/
bilinear.go
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// Copyright 2014 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 portable
import (
"image"
"image/color"
"math"
)
func bilinear(src image.Image, x, y float32) color.Color {
switch src := src.(type) {
case *image.RGBA:
return bilinearRGBA(src, x, y)
case *image.Alpha:
return bilinearAlpha(src, x, y)
case *image.Uniform:
return src.C
default:
return bilinearGeneral(src, x, y)
}
}
func bilinearGeneral(src image.Image, x, y float32) color.RGBA64 {
p := findLinearSrc(src.Bounds(), x, y)
r00, g00, b00, a00 := src.At(p.low.X, p.low.Y).RGBA()
r01, g01, b01, a01 := src.At(p.high.X, p.low.Y).RGBA()
r10, g10, b10, a10 := src.At(p.low.X, p.high.Y).RGBA()
r11, g11, b11, a11 := src.At(p.high.X, p.high.Y).RGBA()
fr := float32(r00) * p.frac00
fg := float32(g00) * p.frac00
fb := float32(b00) * p.frac00
fa := float32(a00) * p.frac00
fr += float32(r01) * p.frac01
fg += float32(g01) * p.frac01
fb += float32(b01) * p.frac01
fa += float32(a01) * p.frac01
fr += float32(r10) * p.frac10
fg += float32(g10) * p.frac10
fb += float32(b10) * p.frac10
fa += float32(a10) * p.frac10
fr += float32(r11) * p.frac11
fg += float32(g11) * p.frac11
fb += float32(b11) * p.frac11
fa += float32(a11) * p.frac11
return color.RGBA64{
R: uint16(fr + 0.5),
G: uint16(fg + 0.5),
B: uint16(fb + 0.5),
A: uint16(fa + 0.5),
}
}
func bilinearRGBA(src *image.RGBA, x, y float32) color.RGBA {
p := findLinearSrc(src.Bounds(), x, y)
// Slice offsets for the surrounding pixels.
off00 := src.PixOffset(p.low.X, p.low.Y)
off01 := src.PixOffset(p.high.X, p.low.Y)
off10 := src.PixOffset(p.low.X, p.high.Y)
off11 := src.PixOffset(p.high.X, p.high.Y)
fr := float32(src.Pix[off00+0]) * p.frac00
fg := float32(src.Pix[off00+1]) * p.frac00
fb := float32(src.Pix[off00+2]) * p.frac00
fa := float32(src.Pix[off00+3]) * p.frac00
fr += float32(src.Pix[off01+0]) * p.frac01
fg += float32(src.Pix[off01+1]) * p.frac01
fb += float32(src.Pix[off01+2]) * p.frac01
fa += float32(src.Pix[off01+3]) * p.frac01
fr += float32(src.Pix[off10+0]) * p.frac10
fg += float32(src.Pix[off10+1]) * p.frac10
fb += float32(src.Pix[off10+2]) * p.frac10
fa += float32(src.Pix[off10+3]) * p.frac10
fr += float32(src.Pix[off11+0]) * p.frac11
fg += float32(src.Pix[off11+1]) * p.frac11
fb += float32(src.Pix[off11+2]) * p.frac11
fa += float32(src.Pix[off11+3]) * p.frac11
return color.RGBA{
R: uint8(fr + 0.5),
G: uint8(fg + 0.5),
B: uint8(fb + 0.5),
A: uint8(fa + 0.5),
}
}
func bilinearAlpha(src *image.Alpha, x, y float32) color.Alpha {
p := findLinearSrc(src.Bounds(), x, y)
// Slice offsets for the surrounding pixels.
off00 := src.PixOffset(p.low.X, p.low.Y)
off01 := src.PixOffset(p.high.X, p.low.Y)
off10 := src.PixOffset(p.low.X, p.high.Y)
off11 := src.PixOffset(p.high.X, p.high.Y)
fa := float32(src.Pix[off00]) * p.frac00
fa += float32(src.Pix[off01]) * p.frac01
fa += float32(src.Pix[off10]) * p.frac10
fa += float32(src.Pix[off11]) * p.frac11
return color.Alpha{A: uint8(fa + 0.5)}
}
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 float32
}
func floor(x float32) float32 { return float32(math.Floor(float64(x))) }
func ceil(x float32) float32 { return float32(math.Ceil(float64(x))) }
func findLinearSrc(b image.Rectangle, sx, sy float32) bilinearSrc {
maxX := float32(b.Max.X)
maxY := float32(b.Max.Y)
minX := float32(b.Min.X)
minY := float32(b.Min.Y)
lowX := floor(sx - 0.5)
lowY := floor(sy - 0.5)
if lowX < minX {
lowX = minX
}
if lowY < minY {
lowY = minY
}
highX := ceil(sx - 0.5)
highY := 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
}