diff options
Diffstat (limited to 'src/image/internal/imageutil/gen.go')
| -rw-r--r-- | src/image/internal/imageutil/gen.go | 172 |
1 files changed, 172 insertions, 0 deletions
diff --git a/src/image/internal/imageutil/gen.go b/src/image/internal/imageutil/gen.go new file mode 100644 index 0000000..65e1e30 --- /dev/null +++ b/src/image/internal/imageutil/gen.go @@ -0,0 +1,172 @@ +// Copyright 2015 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. + +//go:build ignore + +package main + +import ( + "bytes" + "flag" + "fmt" + "go/format" + "log" + "os" +) + +var debug = flag.Bool("debug", false, "") + +func main() { + flag.Parse() + + w := new(bytes.Buffer) + w.WriteString(pre) + for _, sratio := range subsampleRatios { + fmt.Fprintf(w, sratioCase, sratio, sratioLines[sratio]) + } + w.WriteString(post) + + if *debug { + os.Stdout.Write(w.Bytes()) + return + } + out, err := format.Source(w.Bytes()) + if err != nil { + log.Fatal(err) + } + if err := os.WriteFile("impl.go", out, 0660); err != nil { + log.Fatal(err) + } +} + +const pre = `// Code generated by go run gen.go; DO NOT EDIT. + +package imageutil + +import ( + "image" +) + +// DrawYCbCr draws the YCbCr source image on the RGBA destination image with +// r.Min in dst aligned with sp in src. It reports whether the draw was +// successful. If it returns false, no dst pixels were changed. +// +// This function assumes that r is entirely within dst's bounds and the +// translation of r from dst coordinate space to src coordinate space is +// entirely within src's bounds. +func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Point) (ok bool) { + // This function exists in the image/internal/imageutil package because it + // is needed by both the image/draw and image/jpeg packages, but it doesn't + // seem right for one of those two to depend on the other. + // + // Another option is to have this code be exported in the image package, + // but we'd need to make sure we're totally happy with the API (for the + // rest of Go 1 compatibility), and decide if we want to have a more + // general purpose DrawToRGBA method for other image types. One possibility + // is: + // + // func (src *YCbCr) CopyToRGBA(dst *RGBA, dr, sr Rectangle) (effectiveDr, effectiveSr Rectangle) + // + // in the spirit of the built-in copy function for 1-dimensional slices, + // that also allowed a CopyFromRGBA method if needed. + + x0 := (r.Min.X - dst.Rect.Min.X) * 4 + x1 := (r.Max.X - dst.Rect.Min.X) * 4 + y0 := r.Min.Y - dst.Rect.Min.Y + y1 := r.Max.Y - dst.Rect.Min.Y + switch src.SubsampleRatio { +` + +const post = ` + default: + return false + } + return true +} +` + +const sratioCase = ` + case image.YCbCrSubsampleRatio%s: + for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { + dpix := dst.Pix[y*dst.Stride:] + yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) + %s + + // This is an inline version of image/color/ycbcr.go's func YCbCrToRGB. + yy1 := int32(src.Y[yi]) * 0x10101 + cb1 := int32(src.Cb[ci]) - 128 + cr1 := int32(src.Cr[ci]) - 128 + + // The bit twiddling below is equivalent to + // + // r := (yy1 + 91881*cr1) >> 16 + // if r < 0 { + // r = 0 + // } else if r > 0xff { + // r = ^int32(0) + // } + // + // but uses fewer branches and is faster. + // Note that the uint8 type conversion in the return + // statement will convert ^int32(0) to 0xff. + // The code below to compute g and b uses a similar pattern. + r := yy1 + 91881*cr1 + if uint32(r)&0xff000000 == 0 { + r >>= 16 + } else { + r = ^(r >> 31) + } + + g := yy1 - 22554*cb1 - 46802*cr1 + if uint32(g)&0xff000000 == 0 { + g >>= 16 + } else { + g = ^(g >> 31) + } + + b := yy1 + 116130*cb1 + if uint32(b)&0xff000000 == 0 { + b >>= 16 + } else { + b = ^(b >> 31) + } + + + // use a temp slice to hint to the compiler that a single bounds check suffices + rgba := dpix[x : x+4 : len(dpix)] + rgba[0] = uint8(r) + rgba[1] = uint8(g) + rgba[2] = uint8(b) + rgba[3] = 255 + } + } +` + +var subsampleRatios = []string{ + "444", + "422", + "420", + "440", +} + +var sratioLines = map[string]string{ + "444": ` + ci := (sy-src.Rect.Min.Y)*src.CStride + (sp.X - src.Rect.Min.X) + for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 { + `, + "422": ` + ciBase := (sy-src.Rect.Min.Y)*src.CStride - src.Rect.Min.X/2 + for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 { + ci := ciBase + sx/2 + `, + "420": ` + ciBase := (sy/2-src.Rect.Min.Y/2)*src.CStride - src.Rect.Min.X/2 + for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 { + ci := ciBase + sx/2 + `, + "440": ` + ci := (sy/2-src.Rect.Min.Y/2)*src.CStride + (sp.X - src.Rect.Min.X) + for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 { + `, +} |