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// 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
// +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 {
`,
}
|
