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-rw-r--r--src/image/png/writer.go530
1 files changed, 530 insertions, 0 deletions
diff --git a/src/image/png/writer.go b/src/image/png/writer.go
new file mode 100644
index 000000000..df23270ee
--- /dev/null
+++ b/src/image/png/writer.go
@@ -0,0 +1,530 @@
+// Copyright 2009 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 png
+
+import (
+ "bufio"
+ "compress/zlib"
+ "hash/crc32"
+ "image"
+ "image/color"
+ "io"
+ "strconv"
+)
+
+// Encoder configures encoding PNG images.
+type Encoder struct {
+ CompressionLevel CompressionLevel
+}
+
+type encoder struct {
+ enc *Encoder
+ w io.Writer
+ m image.Image
+ cb int
+ err error
+ header [8]byte
+ footer [4]byte
+ tmp [4 * 256]byte
+}
+
+type CompressionLevel int
+
+const (
+ DefaultCompression CompressionLevel = 0
+ NoCompression CompressionLevel = -1
+ BestSpeed CompressionLevel = -2
+ BestCompression CompressionLevel = -3
+
+ // Positive CompressionLevel values are reserved to mean a numeric zlib
+ // compression level, although that is not implemented yet.
+)
+
+// Big-endian.
+func writeUint32(b []uint8, u uint32) {
+ b[0] = uint8(u >> 24)
+ b[1] = uint8(u >> 16)
+ b[2] = uint8(u >> 8)
+ b[3] = uint8(u >> 0)
+}
+
+type opaquer interface {
+ Opaque() bool
+}
+
+// Returns whether or not the image is fully opaque.
+func opaque(m image.Image) bool {
+ if o, ok := m.(opaquer); ok {
+ return o.Opaque()
+ }
+ b := m.Bounds()
+ for y := b.Min.Y; y < b.Max.Y; y++ {
+ for x := b.Min.X; x < b.Max.X; x++ {
+ _, _, _, a := m.At(x, y).RGBA()
+ if a != 0xffff {
+ return false
+ }
+ }
+ }
+ return true
+}
+
+// The absolute value of a byte interpreted as a signed int8.
+func abs8(d uint8) int {
+ if d < 128 {
+ return int(d)
+ }
+ return 256 - int(d)
+}
+
+func (e *encoder) writeChunk(b []byte, name string) {
+ if e.err != nil {
+ return
+ }
+ n := uint32(len(b))
+ if int(n) != len(b) {
+ e.err = UnsupportedError(name + " chunk is too large: " + strconv.Itoa(len(b)))
+ return
+ }
+ writeUint32(e.header[:4], n)
+ e.header[4] = name[0]
+ e.header[5] = name[1]
+ e.header[6] = name[2]
+ e.header[7] = name[3]
+ crc := crc32.NewIEEE()
+ crc.Write(e.header[4:8])
+ crc.Write(b)
+ writeUint32(e.footer[:4], crc.Sum32())
+
+ _, e.err = e.w.Write(e.header[:8])
+ if e.err != nil {
+ return
+ }
+ _, e.err = e.w.Write(b)
+ if e.err != nil {
+ return
+ }
+ _, e.err = e.w.Write(e.footer[:4])
+}
+
+func (e *encoder) writeIHDR() {
+ b := e.m.Bounds()
+ writeUint32(e.tmp[0:4], uint32(b.Dx()))
+ writeUint32(e.tmp[4:8], uint32(b.Dy()))
+ // Set bit depth and color type.
+ switch e.cb {
+ case cbG8:
+ e.tmp[8] = 8
+ e.tmp[9] = ctGrayscale
+ case cbTC8:
+ e.tmp[8] = 8
+ e.tmp[9] = ctTrueColor
+ case cbP8:
+ e.tmp[8] = 8
+ e.tmp[9] = ctPaletted
+ case cbTCA8:
+ e.tmp[8] = 8
+ e.tmp[9] = ctTrueColorAlpha
+ case cbG16:
+ e.tmp[8] = 16
+ e.tmp[9] = ctGrayscale
+ case cbTC16:
+ e.tmp[8] = 16
+ e.tmp[9] = ctTrueColor
+ case cbTCA16:
+ e.tmp[8] = 16
+ e.tmp[9] = ctTrueColorAlpha
+ }
+ e.tmp[10] = 0 // default compression method
+ e.tmp[11] = 0 // default filter method
+ e.tmp[12] = 0 // non-interlaced
+ e.writeChunk(e.tmp[:13], "IHDR")
+}
+
+func (e *encoder) writePLTEAndTRNS(p color.Palette) {
+ if len(p) < 1 || len(p) > 256 {
+ e.err = FormatError("bad palette length: " + strconv.Itoa(len(p)))
+ return
+ }
+ last := -1
+ for i, c := range p {
+ c1 := color.NRGBAModel.Convert(c).(color.NRGBA)
+ e.tmp[3*i+0] = c1.R
+ e.tmp[3*i+1] = c1.G
+ e.tmp[3*i+2] = c1.B
+ if c1.A != 0xff {
+ last = i
+ }
+ e.tmp[3*256+i] = c1.A
+ }
+ e.writeChunk(e.tmp[:3*len(p)], "PLTE")
+ if last != -1 {
+ e.writeChunk(e.tmp[3*256:3*256+1+last], "tRNS")
+ }
+}
+
+// An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks,
+// including an 8-byte header and 4-byte CRC checksum per Write call. Such calls
+// should be relatively infrequent, since writeIDATs uses a bufio.Writer.
+//
+// This method should only be called from writeIDATs (via writeImage).
+// No other code should treat an encoder as an io.Writer.
+func (e *encoder) Write(b []byte) (int, error) {
+ e.writeChunk(b, "IDAT")
+ if e.err != nil {
+ return 0, e.err
+ }
+ return len(b), nil
+}
+
+// Chooses the filter to use for encoding the current row, and applies it.
+// The return value is the index of the filter and also of the row in cr that has had it applied.
+func filter(cr *[nFilter][]byte, pr []byte, bpp int) int {
+ // We try all five filter types, and pick the one that minimizes the sum of absolute differences.
+ // This is the same heuristic that libpng uses, although the filters are attempted in order of
+ // estimated most likely to be minimal (ftUp, ftPaeth, ftNone, ftSub, ftAverage), rather than
+ // in their enumeration order (ftNone, ftSub, ftUp, ftAverage, ftPaeth).
+ cdat0 := cr[0][1:]
+ cdat1 := cr[1][1:]
+ cdat2 := cr[2][1:]
+ cdat3 := cr[3][1:]
+ cdat4 := cr[4][1:]
+ pdat := pr[1:]
+ n := len(cdat0)
+
+ // The up filter.
+ sum := 0
+ for i := 0; i < n; i++ {
+ cdat2[i] = cdat0[i] - pdat[i]
+ sum += abs8(cdat2[i])
+ }
+ best := sum
+ filter := ftUp
+
+ // The Paeth filter.
+ sum = 0
+ for i := 0; i < bpp; i++ {
+ cdat4[i] = cdat0[i] - pdat[i]
+ sum += abs8(cdat4[i])
+ }
+ for i := bpp; i < n; i++ {
+ cdat4[i] = cdat0[i] - paeth(cdat0[i-bpp], pdat[i], pdat[i-bpp])
+ sum += abs8(cdat4[i])
+ if sum >= best {
+ break
+ }
+ }
+ if sum < best {
+ best = sum
+ filter = ftPaeth
+ }
+
+ // The none filter.
+ sum = 0
+ for i := 0; i < n; i++ {
+ sum += abs8(cdat0[i])
+ if sum >= best {
+ break
+ }
+ }
+ if sum < best {
+ best = sum
+ filter = ftNone
+ }
+
+ // The sub filter.
+ sum = 0
+ for i := 0; i < bpp; i++ {
+ cdat1[i] = cdat0[i]
+ sum += abs8(cdat1[i])
+ }
+ for i := bpp; i < n; i++ {
+ cdat1[i] = cdat0[i] - cdat0[i-bpp]
+ sum += abs8(cdat1[i])
+ if sum >= best {
+ break
+ }
+ }
+ if sum < best {
+ best = sum
+ filter = ftSub
+ }
+
+ // The average filter.
+ sum = 0
+ for i := 0; i < bpp; i++ {
+ cdat3[i] = cdat0[i] - pdat[i]/2
+ sum += abs8(cdat3[i])
+ }
+ for i := bpp; i < n; i++ {
+ cdat3[i] = cdat0[i] - uint8((int(cdat0[i-bpp])+int(pdat[i]))/2)
+ sum += abs8(cdat3[i])
+ if sum >= best {
+ break
+ }
+ }
+ if sum < best {
+ best = sum
+ filter = ftAverage
+ }
+
+ return filter
+}
+
+func writeImage(w io.Writer, m image.Image, cb int, level int) error {
+ zw, err := zlib.NewWriterLevel(w, level)
+ if err != nil {
+ return err
+ }
+ defer zw.Close()
+
+ bpp := 0 // Bytes per pixel.
+
+ switch cb {
+ case cbG8:
+ bpp = 1
+ case cbTC8:
+ bpp = 3
+ case cbP8:
+ bpp = 1
+ case cbTCA8:
+ bpp = 4
+ case cbTC16:
+ bpp = 6
+ case cbTCA16:
+ bpp = 8
+ case cbG16:
+ bpp = 2
+ }
+ // cr[*] and pr are the bytes for the current and previous row.
+ // cr[0] is unfiltered (or equivalently, filtered with the ftNone filter).
+ // cr[ft], for non-zero filter types ft, are buffers for transforming cr[0] under the
+ // other PNG filter types. These buffers are allocated once and re-used for each row.
+ // The +1 is for the per-row filter type, which is at cr[*][0].
+ b := m.Bounds()
+ var cr [nFilter][]uint8
+ for i := range cr {
+ cr[i] = make([]uint8, 1+bpp*b.Dx())
+ cr[i][0] = uint8(i)
+ }
+ pr := make([]uint8, 1+bpp*b.Dx())
+
+ gray, _ := m.(*image.Gray)
+ rgba, _ := m.(*image.RGBA)
+ paletted, _ := m.(*image.Paletted)
+ nrgba, _ := m.(*image.NRGBA)
+
+ for y := b.Min.Y; y < b.Max.Y; y++ {
+ // Convert from colors to bytes.
+ i := 1
+ switch cb {
+ case cbG8:
+ if gray != nil {
+ offset := (y - b.Min.Y) * gray.Stride
+ copy(cr[0][1:], gray.Pix[offset:offset+b.Dx()])
+ } else {
+ for x := b.Min.X; x < b.Max.X; x++ {
+ c := color.GrayModel.Convert(m.At(x, y)).(color.Gray)
+ cr[0][i] = c.Y
+ i++
+ }
+ }
+ case cbTC8:
+ // We have previously verified that the alpha value is fully opaque.
+ cr0 := cr[0]
+ stride, pix := 0, []byte(nil)
+ if rgba != nil {
+ stride, pix = rgba.Stride, rgba.Pix
+ } else if nrgba != nil {
+ stride, pix = nrgba.Stride, nrgba.Pix
+ }
+ if stride != 0 {
+ j0 := (y - b.Min.Y) * stride
+ j1 := j0 + b.Dx()*4
+ for j := j0; j < j1; j += 4 {
+ cr0[i+0] = pix[j+0]
+ cr0[i+1] = pix[j+1]
+ cr0[i+2] = pix[j+2]
+ i += 3
+ }
+ } else {
+ for x := b.Min.X; x < b.Max.X; x++ {
+ r, g, b, _ := m.At(x, y).RGBA()
+ cr0[i+0] = uint8(r >> 8)
+ cr0[i+1] = uint8(g >> 8)
+ cr0[i+2] = uint8(b >> 8)
+ i += 3
+ }
+ }
+ case cbP8:
+ if paletted != nil {
+ offset := (y - b.Min.Y) * paletted.Stride
+ copy(cr[0][1:], paletted.Pix[offset:offset+b.Dx()])
+ } else {
+ pi := m.(image.PalettedImage)
+ for x := b.Min.X; x < b.Max.X; x++ {
+ cr[0][i] = pi.ColorIndexAt(x, y)
+ i += 1
+ }
+ }
+ case cbTCA8:
+ if nrgba != nil {
+ offset := (y - b.Min.Y) * nrgba.Stride
+ copy(cr[0][1:], nrgba.Pix[offset:offset+b.Dx()*4])
+ } else {
+ // Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
+ for x := b.Min.X; x < b.Max.X; x++ {
+ c := color.NRGBAModel.Convert(m.At(x, y)).(color.NRGBA)
+ cr[0][i+0] = c.R
+ cr[0][i+1] = c.G
+ cr[0][i+2] = c.B
+ cr[0][i+3] = c.A
+ i += 4
+ }
+ }
+ case cbG16:
+ for x := b.Min.X; x < b.Max.X; x++ {
+ c := color.Gray16Model.Convert(m.At(x, y)).(color.Gray16)
+ cr[0][i+0] = uint8(c.Y >> 8)
+ cr[0][i+1] = uint8(c.Y)
+ i += 2
+ }
+ case cbTC16:
+ // We have previously verified that the alpha value is fully opaque.
+ for x := b.Min.X; x < b.Max.X; x++ {
+ r, g, b, _ := m.At(x, y).RGBA()
+ cr[0][i+0] = uint8(r >> 8)
+ cr[0][i+1] = uint8(r)
+ cr[0][i+2] = uint8(g >> 8)
+ cr[0][i+3] = uint8(g)
+ cr[0][i+4] = uint8(b >> 8)
+ cr[0][i+5] = uint8(b)
+ i += 6
+ }
+ case cbTCA16:
+ // Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
+ for x := b.Min.X; x < b.Max.X; x++ {
+ c := color.NRGBA64Model.Convert(m.At(x, y)).(color.NRGBA64)
+ cr[0][i+0] = uint8(c.R >> 8)
+ cr[0][i+1] = uint8(c.R)
+ cr[0][i+2] = uint8(c.G >> 8)
+ cr[0][i+3] = uint8(c.G)
+ cr[0][i+4] = uint8(c.B >> 8)
+ cr[0][i+5] = uint8(c.B)
+ cr[0][i+6] = uint8(c.A >> 8)
+ cr[0][i+7] = uint8(c.A)
+ i += 8
+ }
+ }
+
+ // Apply the filter.
+ f := ftNone
+ if level != zlib.NoCompression {
+ f = filter(&cr, pr, bpp)
+ }
+
+ // Write the compressed bytes.
+ if _, err := zw.Write(cr[f]); err != nil {
+ return err
+ }
+
+ // The current row for y is the previous row for y+1.
+ pr, cr[0] = cr[0], pr
+ }
+ return nil
+}
+
+// Write the actual image data to one or more IDAT chunks.
+func (e *encoder) writeIDATs() {
+ if e.err != nil {
+ return
+ }
+ var bw *bufio.Writer
+ bw = bufio.NewWriterSize(e, 1<<15)
+ e.err = writeImage(bw, e.m, e.cb, levelToZlib(e.enc.CompressionLevel))
+ if e.err != nil {
+ return
+ }
+ e.err = bw.Flush()
+}
+
+// This function is required because we want the zero value of
+// Encoder.CompressionLevel to map to zlib.DefaultCompression.
+func levelToZlib(l CompressionLevel) int {
+ switch l {
+ case DefaultCompression:
+ return zlib.DefaultCompression
+ case NoCompression:
+ return zlib.NoCompression
+ case BestSpeed:
+ return zlib.BestSpeed
+ case BestCompression:
+ return zlib.BestCompression
+ default:
+ return zlib.DefaultCompression
+ }
+}
+
+func (e *encoder) writeIEND() { e.writeChunk(nil, "IEND") }
+
+// Encode writes the Image m to w in PNG format. Any Image may be
+// encoded, but images that are not image.NRGBA might be encoded lossily.
+func Encode(w io.Writer, m image.Image) error {
+ var e Encoder
+ return e.Encode(w, m)
+}
+
+// Encode writes the Image m to w in PNG format.
+func (enc *Encoder) Encode(w io.Writer, m image.Image) error {
+ // Obviously, negative widths and heights are invalid. Furthermore, the PNG
+ // spec section 11.2.2 says that zero is invalid. Excessively large images are
+ // also rejected.
+ mw, mh := int64(m.Bounds().Dx()), int64(m.Bounds().Dy())
+ if mw <= 0 || mh <= 0 || mw >= 1<<32 || mh >= 1<<32 {
+ return FormatError("invalid image size: " + strconv.FormatInt(mw, 10) + "x" + strconv.FormatInt(mh, 10))
+ }
+
+ var e encoder
+ e.enc = enc
+ e.w = w
+ e.m = m
+
+ var pal color.Palette
+ // cbP8 encoding needs PalettedImage's ColorIndexAt method.
+ if _, ok := m.(image.PalettedImage); ok {
+ pal, _ = m.ColorModel().(color.Palette)
+ }
+ if pal != nil {
+ e.cb = cbP8
+ } else {
+ switch m.ColorModel() {
+ case color.GrayModel:
+ e.cb = cbG8
+ case color.Gray16Model:
+ e.cb = cbG16
+ case color.RGBAModel, color.NRGBAModel, color.AlphaModel:
+ if opaque(m) {
+ e.cb = cbTC8
+ } else {
+ e.cb = cbTCA8
+ }
+ default:
+ if opaque(m) {
+ e.cb = cbTC16
+ } else {
+ e.cb = cbTCA16
+ }
+ }
+ }
+
+ _, e.err = io.WriteString(w, pngHeader)
+ e.writeIHDR()
+ if pal != nil {
+ e.writePLTEAndTRNS(pal)
+ }
+ e.writeIDATs()
+ e.writeIEND()
+ return e.err
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-05-20 16:39:14 +0000