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image/png: fix encoding of images that don't start at (0, 0).
R=r CC=golang-dev https://golang.org/cl/4560049
This commit is contained in:
Nigel Tao
parent
5d5d84f3df
commit
a479bc8d02
@ -174,7 +174,7 @@ func (e *encoder) Write(b []byte) (int, os.Error) {
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// Chooses the filter to use for encoding the current row, and applies it.
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// The return value is the index of the filter and also of the row in cr that has had it applied.
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func filter(cr [][]byte, pr []byte, bpp int) int {
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func filter(cr *[nFilter][]byte, pr []byte, bpp int) int {
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// We try all five filter types, and pick the one that minimizes the sum of absolute differences.
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// This is the same heuristic that libpng uses, although the filters are attempted in order of
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// estimated most likely to be minimal (ftUp, ftPaeth, ftNone, ftSub, ftAverage), rather than
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@ -304,7 +304,7 @@ func writeImage(w io.Writer, m image.Image, cb int) os.Error {
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// The +1 is for the per-row filter type, which is at cr[*][0].
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b := m.Bounds()
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var cr [nFilter][]uint8
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for i := 0; i < len(cr); i++ {
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for i := range cr {
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cr[i] = make([]uint8, 1+bpp*b.Dx())
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cr[i][0] = uint8(i)
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}
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@ -312,78 +312,84 @@ func writeImage(w io.Writer, m image.Image, cb int) os.Error {
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for y := b.Min.Y; y < b.Max.Y; y++ {
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// Convert from colors to bytes.
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i := 1
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switch cb {
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case cbG8:
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for x := b.Min.X; x < b.Max.X; x++ {
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c := image.GrayColorModel.Convert(m.At(x, y)).(image.GrayColor)
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cr[0][x+1] = c.Y
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cr[0][i] = c.Y
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i++
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}
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case cbTC8:
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// We have previously verified that the alpha value is fully opaque.
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cr0 := cr[0]
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if rgba != nil {
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yoff := y * rgba.Stride
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xoff := 3*b.Min.X + 1
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for _, color := range rgba.Pix[yoff+b.Min.X : yoff+b.Max.X] {
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cr0[xoff] = color.R
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cr0[xoff+1] = color.G
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cr0[xoff+2] = color.B
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xoff += 3
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cr0[i+0] = color.R
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cr0[i+1] = color.G
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cr0[i+2] = color.B
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i += 3
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}
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} else {
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for x := b.Min.X; x < b.Max.X; x++ {
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r, g, b, _ := m.At(x, y).RGBA()
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cr0[3*x+1] = uint8(r >> 8)
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cr0[3*x+2] = uint8(g >> 8)
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cr0[3*x+3] = uint8(b >> 8)
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cr0[i+0] = uint8(r >> 8)
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cr0[i+1] = uint8(g >> 8)
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cr0[i+2] = uint8(b >> 8)
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i += 3
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}
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}
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case cbP8:
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rowOffset := y * paletted.Stride
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copy(cr[0][b.Min.X+1:], paletted.Pix[rowOffset+b.Min.X:rowOffset+b.Max.X])
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copy(cr[0][1:], paletted.Pix[rowOffset+b.Min.X:rowOffset+b.Max.X])
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case cbTCA8:
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// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
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for x := b.Min.X; x < b.Max.X; x++ {
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c := image.NRGBAColorModel.Convert(m.At(x, y)).(image.NRGBAColor)
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cr[0][4*x+1] = c.R
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cr[0][4*x+2] = c.G
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cr[0][4*x+3] = c.B
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cr[0][4*x+4] = c.A
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cr[0][i+0] = c.R
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cr[0][i+1] = c.G
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cr[0][i+2] = c.B
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cr[0][i+3] = c.A
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i += 4
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}
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case cbG16:
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for x := b.Min.X; x < b.Max.X; x++ {
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c := image.Gray16ColorModel.Convert(m.At(x, y)).(image.Gray16Color)
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cr[0][2*x+1] = uint8(c.Y >> 8)
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cr[0][2*x+2] = uint8(c.Y)
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cr[0][i+0] = uint8(c.Y >> 8)
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cr[0][i+1] = uint8(c.Y)
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i += 2
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}
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case cbTC16:
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// We have previously verified that the alpha value is fully opaque.
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for x := b.Min.X; x < b.Max.X; x++ {
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// We have previously verified that the alpha value is fully opaque.
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r, g, b, _ := m.At(x, y).RGBA()
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cr[0][6*x+1] = uint8(r >> 8)
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cr[0][6*x+2] = uint8(r)
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cr[0][6*x+3] = uint8(g >> 8)
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cr[0][6*x+4] = uint8(g)
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cr[0][6*x+5] = uint8(b >> 8)
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cr[0][6*x+6] = uint8(b)
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cr[0][i+0] = uint8(r >> 8)
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cr[0][i+1] = uint8(r)
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cr[0][i+2] = uint8(g >> 8)
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cr[0][i+3] = uint8(g)
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cr[0][i+4] = uint8(b >> 8)
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cr[0][i+5] = uint8(b)
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i += 6
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}
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case cbTCA16:
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// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
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for x := b.Min.X; x < b.Max.X; x++ {
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c := image.NRGBA64ColorModel.Convert(m.At(x, y)).(image.NRGBA64Color)
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cr[0][8*x+1] = uint8(c.R >> 8)
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cr[0][8*x+2] = uint8(c.R)
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cr[0][8*x+3] = uint8(c.G >> 8)
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cr[0][8*x+4] = uint8(c.G)
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cr[0][8*x+5] = uint8(c.B >> 8)
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cr[0][8*x+6] = uint8(c.B)
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cr[0][8*x+7] = uint8(c.A >> 8)
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cr[0][8*x+8] = uint8(c.A)
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cr[0][i+0] = uint8(c.R >> 8)
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cr[0][i+1] = uint8(c.R)
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cr[0][i+2] = uint8(c.G >> 8)
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cr[0][i+3] = uint8(c.G)
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cr[0][i+4] = uint8(c.B >> 8)
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cr[0][i+5] = uint8(c.B)
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cr[0][i+6] = uint8(c.A >> 8)
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cr[0][i+7] = uint8(c.A)
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i += 8
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}
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}
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// Apply the filter.
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f := filter(cr[0:nFilter], pr, bpp)
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f := filter(&cr, pr, bpp)
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// Write the compressed bytes.
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_, err = zw.Write(cr[f])
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@ -5,9 +5,9 @@
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package png
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import (
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"bytes"
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"fmt"
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"image"
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"io"
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"io/ioutil"
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"os"
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"testing"
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@ -15,21 +15,38 @@ import (
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func diff(m0, m1 image.Image) os.Error {
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b0, b1 := m0.Bounds(), m1.Bounds()
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if !b0.Eq(b1) {
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if !b0.Size().Eq(b1.Size()) {
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return fmt.Errorf("dimensions differ: %v vs %v", b0, b1)
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}
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dx := b1.Min.X - b0.Min.X
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dy := b1.Min.Y - b0.Min.Y
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for y := b0.Min.Y; y < b0.Max.Y; y++ {
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for x := b0.Min.X; x < b0.Max.X; x++ {
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r0, g0, b0, a0 := m0.At(x, y).RGBA()
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r1, g1, b1, a1 := m1.At(x, y).RGBA()
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c0 := m0.At(x, y)
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c1 := m1.At(x+dx, y+dy)
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r0, g0, b0, a0 := c0.RGBA()
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r1, g1, b1, a1 := c1.RGBA()
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if r0 != r1 || g0 != g1 || b0 != b1 || a0 != a1 {
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return fmt.Errorf("colors differ at (%d, %d): %v vs %v", x, y, m0.At(x, y), m1.At(x, y))
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return fmt.Errorf("colors differ at (%d, %d): %v vs %v", x, y, c0, c1)
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}
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}
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}
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return nil
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}
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func encodeDecode(m image.Image) (image.Image, os.Error) {
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b := bytes.NewBuffer(nil)
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err := Encode(b, m)
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if err != nil {
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return nil, err
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}
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m, err = Decode(b)
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if err != nil {
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return nil, err
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}
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return m, nil
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}
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func TestWriter(t *testing.T) {
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// The filenames variable is declared in reader_test.go.
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names := filenames
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@ -44,26 +61,16 @@ func TestWriter(t *testing.T) {
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t.Error(fn, err)
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continue
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}
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// Read the image again, and push it through a pipe that encodes at the write end, and decodes at the read end.
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pr, pw := io.Pipe()
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defer pr.Close()
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go func() {
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defer pw.Close()
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m1, err := readPng(qfn)
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if err != nil {
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t.Error(fn, err)
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return
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}
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err = Encode(pw, m1)
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if err != nil {
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t.Error(fn, err)
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return
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}
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}()
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m2, err := Decode(pr)
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// Read the image again, encode it, and decode it.
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m1, err := readPng(qfn)
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if err != nil {
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t.Error(fn, err)
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continue
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return
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}
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m2, err := encodeDecode(m1)
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if err != nil {
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t.Error(fn, err)
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return
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}
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// Compare the two.
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err = diff(m0, m2)
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@ -74,6 +81,26 @@ func TestWriter(t *testing.T) {
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}
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}
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func TestSubimage(t *testing.T) {
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m0 := image.NewRGBA(256, 256)
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for y := 0; y < 256; y++ {
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for x := 0; x < 256; x++ {
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m0.Set(x, y, image.RGBAColor{uint8(x), uint8(y), 0, 255})
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}
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}
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m0.Rect = image.Rect(50, 30, 250, 130)
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m1, err := encodeDecode(m0)
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if err != nil {
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t.Error(err)
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return
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}
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err = diff(m0, m1)
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if err != nil {
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t.Error(err)
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return
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}
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}
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func BenchmarkEncodePaletted(b *testing.B) {
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b.StopTimer()
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img := image.NewPaletted(640, 480,
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