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Diffstat (limited to 'vendor/golang.org/x/image/vp8l/transform.go')
-rw-r--r--vendor/golang.org/x/image/vp8l/transform.go299
1 files changed, 299 insertions, 0 deletions
diff --git a/vendor/golang.org/x/image/vp8l/transform.go b/vendor/golang.org/x/image/vp8l/transform.go
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+++ b/vendor/golang.org/x/image/vp8l/transform.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 vp8l
+
+// This file deals with image transforms, specified in section 3.
+
+// nTiles returns the number of tiles needed to cover size pixels, where each
+// tile's side is 1<<bits pixels long.
+func nTiles(size int32, bits uint32) int32 {
+ return (size + 1<<bits - 1) >> bits
+}
+
+const (
+ transformTypePredictor = 0
+ transformTypeCrossColor = 1
+ transformTypeSubtractGreen = 2
+ transformTypeColorIndexing = 3
+ nTransformTypes = 4
+)
+
+// transform holds the parameters for an invertible transform.
+type transform struct {
+ // transformType is the type of the transform.
+ transformType uint32
+ // oldWidth is the width of the image before transformation (or
+ // equivalently, after inverse transformation). The color-indexing
+ // transform can reduce the width. For example, a 50-pixel-wide
+ // image that only needs 4 bits (half a byte) per color index can
+ // be transformed into a 25-pixel-wide image.
+ oldWidth int32
+ // bits is the log-2 size of the transform's tiles, for the predictor
+ // and cross-color transforms. 8>>bits is the number of bits per
+ // color index, for the color-index transform.
+ bits uint32
+ // pix is the tile values, for the predictor and cross-color
+ // transforms, and the color palette, for the color-index transform.
+ pix []byte
+}
+
+var inverseTransforms = [nTransformTypes]func(*transform, []byte, int32) []byte{
+ transformTypePredictor: inversePredictor,
+ transformTypeCrossColor: inverseCrossColor,
+ transformTypeSubtractGreen: inverseSubtractGreen,
+ transformTypeColorIndexing: inverseColorIndexing,
+}
+
+func inversePredictor(t *transform, pix []byte, h int32) []byte {
+ if t.oldWidth == 0 || h == 0 {
+ return pix
+ }
+ // The first pixel's predictor is mode 0 (opaque black).
+ pix[3] += 0xff
+ p, mask := int32(4), int32(1)<<t.bits-1
+ for x := int32(1); x < t.oldWidth; x++ {
+ // The rest of the first row's predictor is mode 1 (L).
+ pix[p+0] += pix[p-4]
+ pix[p+1] += pix[p-3]
+ pix[p+2] += pix[p-2]
+ pix[p+3] += pix[p-1]
+ p += 4
+ }
+ top, tilesPerRow := 0, nTiles(t.oldWidth, t.bits)
+ for y := int32(1); y < h; y++ {
+ // The first column's predictor is mode 2 (T).
+ pix[p+0] += pix[top+0]
+ pix[p+1] += pix[top+1]
+ pix[p+2] += pix[top+2]
+ pix[p+3] += pix[top+3]
+ p, top = p+4, top+4
+
+ q := 4 * (y >> t.bits) * tilesPerRow
+ predictorMode := t.pix[q+1] & 0x0f
+ q += 4
+ for x := int32(1); x < t.oldWidth; x++ {
+ if x&mask == 0 {
+ predictorMode = t.pix[q+1] & 0x0f
+ q += 4
+ }
+ switch predictorMode {
+ case 0: // Opaque black.
+ pix[p+3] += 0xff
+
+ case 1: // L.
+ pix[p+0] += pix[p-4]
+ pix[p+1] += pix[p-3]
+ pix[p+2] += pix[p-2]
+ pix[p+3] += pix[p-1]
+
+ case 2: // T.
+ pix[p+0] += pix[top+0]
+ pix[p+1] += pix[top+1]
+ pix[p+2] += pix[top+2]
+ pix[p+3] += pix[top+3]
+
+ case 3: // TR.
+ pix[p+0] += pix[top+4]
+ pix[p+1] += pix[top+5]
+ pix[p+2] += pix[top+6]
+ pix[p+3] += pix[top+7]
+
+ case 4: // TL.
+ pix[p+0] += pix[top-4]
+ pix[p+1] += pix[top-3]
+ pix[p+2] += pix[top-2]
+ pix[p+3] += pix[top-1]
+
+ case 5: // Average2(Average2(L, TR), T).
+ pix[p+0] += avg2(avg2(pix[p-4], pix[top+4]), pix[top+0])
+ pix[p+1] += avg2(avg2(pix[p-3], pix[top+5]), pix[top+1])
+ pix[p+2] += avg2(avg2(pix[p-2], pix[top+6]), pix[top+2])
+ pix[p+3] += avg2(avg2(pix[p-1], pix[top+7]), pix[top+3])
+
+ case 6: // Average2(L, TL).
+ pix[p+0] += avg2(pix[p-4], pix[top-4])
+ pix[p+1] += avg2(pix[p-3], pix[top-3])
+ pix[p+2] += avg2(pix[p-2], pix[top-2])
+ pix[p+3] += avg2(pix[p-1], pix[top-1])
+
+ case 7: // Average2(L, T).
+ pix[p+0] += avg2(pix[p-4], pix[top+0])
+ pix[p+1] += avg2(pix[p-3], pix[top+1])
+ pix[p+2] += avg2(pix[p-2], pix[top+2])
+ pix[p+3] += avg2(pix[p-1], pix[top+3])
+
+ case 8: // Average2(TL, T).
+ pix[p+0] += avg2(pix[top-4], pix[top+0])
+ pix[p+1] += avg2(pix[top-3], pix[top+1])
+ pix[p+2] += avg2(pix[top-2], pix[top+2])
+ pix[p+3] += avg2(pix[top-1], pix[top+3])
+
+ case 9: // Average2(T, TR).
+ pix[p+0] += avg2(pix[top+0], pix[top+4])
+ pix[p+1] += avg2(pix[top+1], pix[top+5])
+ pix[p+2] += avg2(pix[top+2], pix[top+6])
+ pix[p+3] += avg2(pix[top+3], pix[top+7])
+
+ case 10: // Average2(Average2(L, TL), Average2(T, TR)).
+ pix[p+0] += avg2(avg2(pix[p-4], pix[top-4]), avg2(pix[top+0], pix[top+4]))
+ pix[p+1] += avg2(avg2(pix[p-3], pix[top-3]), avg2(pix[top+1], pix[top+5]))
+ pix[p+2] += avg2(avg2(pix[p-2], pix[top-2]), avg2(pix[top+2], pix[top+6]))
+ pix[p+3] += avg2(avg2(pix[p-1], pix[top-1]), avg2(pix[top+3], pix[top+7]))
+
+ case 11: // Select(L, T, TL).
+ l0 := int32(pix[p-4])
+ l1 := int32(pix[p-3])
+ l2 := int32(pix[p-2])
+ l3 := int32(pix[p-1])
+ c0 := int32(pix[top-4])
+ c1 := int32(pix[top-3])
+ c2 := int32(pix[top-2])
+ c3 := int32(pix[top-1])
+ t0 := int32(pix[top+0])
+ t1 := int32(pix[top+1])
+ t2 := int32(pix[top+2])
+ t3 := int32(pix[top+3])
+ l := abs(c0-t0) + abs(c1-t1) + abs(c2-t2) + abs(c3-t3)
+ t := abs(c0-l0) + abs(c1-l1) + abs(c2-l2) + abs(c3-l3)
+ if l < t {
+ pix[p+0] += uint8(l0)
+ pix[p+1] += uint8(l1)
+ pix[p+2] += uint8(l2)
+ pix[p+3] += uint8(l3)
+ } else {
+ pix[p+0] += uint8(t0)
+ pix[p+1] += uint8(t1)
+ pix[p+2] += uint8(t2)
+ pix[p+3] += uint8(t3)
+ }
+
+ case 12: // ClampAddSubtractFull(L, T, TL).
+ pix[p+0] += clampAddSubtractFull(pix[p-4], pix[top+0], pix[top-4])
+ pix[p+1] += clampAddSubtractFull(pix[p-3], pix[top+1], pix[top-3])
+ pix[p+2] += clampAddSubtractFull(pix[p-2], pix[top+2], pix[top-2])
+ pix[p+3] += clampAddSubtractFull(pix[p-1], pix[top+3], pix[top-1])
+
+ case 13: // ClampAddSubtractHalf(Average2(L, T), TL).
+ pix[p+0] += clampAddSubtractHalf(avg2(pix[p-4], pix[top+0]), pix[top-4])
+ pix[p+1] += clampAddSubtractHalf(avg2(pix[p-3], pix[top+1]), pix[top-3])
+ pix[p+2] += clampAddSubtractHalf(avg2(pix[p-2], pix[top+2]), pix[top-2])
+ pix[p+3] += clampAddSubtractHalf(avg2(pix[p-1], pix[top+3]), pix[top-1])
+ }
+ p, top = p+4, top+4
+ }
+ }
+ return pix
+}
+
+func inverseCrossColor(t *transform, pix []byte, h int32) []byte {
+ var greenToRed, greenToBlue, redToBlue int32
+ p, mask, tilesPerRow := int32(0), int32(1)<<t.bits-1, nTiles(t.oldWidth, t.bits)
+ for y := int32(0); y < h; y++ {
+ q := 4 * (y >> t.bits) * tilesPerRow
+ for x := int32(0); x < t.oldWidth; x++ {
+ if x&mask == 0 {
+ redToBlue = int32(int8(t.pix[q+0]))
+ greenToBlue = int32(int8(t.pix[q+1]))
+ greenToRed = int32(int8(t.pix[q+2]))
+ q += 4
+ }
+ red := pix[p+0]
+ green := pix[p+1]
+ blue := pix[p+2]
+ red += uint8(uint32(greenToRed*int32(int8(green))) >> 5)
+ blue += uint8(uint32(greenToBlue*int32(int8(green))) >> 5)
+ blue += uint8(uint32(redToBlue*int32(int8(red))) >> 5)
+ pix[p+0] = red
+ pix[p+2] = blue
+ p += 4
+ }
+ }
+ return pix
+}
+
+func inverseSubtractGreen(t *transform, pix []byte, h int32) []byte {
+ for p := 0; p < len(pix); p += 4 {
+ green := pix[p+1]
+ pix[p+0] += green
+ pix[p+2] += green
+ }
+ return pix
+}
+
+func inverseColorIndexing(t *transform, pix []byte, h int32) []byte {
+ if t.bits == 0 {
+ for p := 0; p < len(pix); p += 4 {
+ i := 4 * uint32(pix[p+1])
+ pix[p+0] = t.pix[i+0]
+ pix[p+1] = t.pix[i+1]
+ pix[p+2] = t.pix[i+2]
+ pix[p+3] = t.pix[i+3]
+ }
+ return pix
+ }
+
+ vMask, xMask, bitsPerPixel := uint32(0), int32(0), uint32(8>>t.bits)
+ switch t.bits {
+ case 1:
+ vMask, xMask = 0x0f, 0x01
+ case 2:
+ vMask, xMask = 0x03, 0x03
+ case 3:
+ vMask, xMask = 0x01, 0x07
+ }
+
+ d, p, v, dst := 0, 0, uint32(0), make([]byte, 4*t.oldWidth*h)
+ for y := int32(0); y < h; y++ {
+ for x := int32(0); x < t.oldWidth; x++ {
+ if x&xMask == 0 {
+ v = uint32(pix[p+1])
+ p += 4
+ }
+
+ i := 4 * (v & vMask)
+ dst[d+0] = t.pix[i+0]
+ dst[d+1] = t.pix[i+1]
+ dst[d+2] = t.pix[i+2]
+ dst[d+3] = t.pix[i+3]
+ d += 4
+
+ v >>= bitsPerPixel
+ }
+ }
+ return dst
+}
+
+func abs(x int32) int32 {
+ if x < 0 {
+ return -x
+ }
+ return x
+}
+
+func avg2(a, b uint8) uint8 {
+ return uint8((int32(a) + int32(b)) / 2)
+}
+
+func clampAddSubtractFull(a, b, c uint8) uint8 {
+ x := int32(a) + int32(b) - int32(c)
+ if x < 0 {
+ return 0
+ }
+ if x > 255 {
+ return 255
+ }
+ return uint8(x)
+}
+
+func clampAddSubtractHalf(a, b uint8) uint8 {
+ x := int32(a) + (int32(a)-int32(b))/2
+ if x < 0 {
+ return 0
+ }
+ if x > 255 {
+ return 255
+ }
+ return uint8(x)
+}