691 lines
20 KiB
Go
691 lines
20 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package draw provides image composition functions.
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//
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// See "The Go image/draw package" for an introduction to this package:
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// https://golang.org/doc/articles/image_draw.html
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package draw
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import (
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"image"
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"image/color"
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"image/internal/imageutil"
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)
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// m is the maximum color value returned by image.Color.RGBA.
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const m = 1<<16 - 1
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// Image is an image.Image with a Set method to change a single pixel.
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type Image interface {
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image.Image
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Set(x, y int, c color.Color)
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}
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// Quantizer produces a palette for an image.
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type Quantizer interface {
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// Quantize appends up to cap(p) - len(p) colors to p and returns the
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// updated palette suitable for converting m to a paletted image.
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Quantize(p color.Palette, m image.Image) color.Palette
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}
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// Op is a Porter-Duff compositing operator.
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type Op int
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const (
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// Over specifies ``(src in mask) over dst''.
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Over Op = iota
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// Src specifies ``src in mask''.
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Src
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)
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// Draw implements the Drawer interface by calling the Draw function with this
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// Op.
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func (op Op) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point) {
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DrawMask(dst, r, src, sp, nil, image.Point{}, op)
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}
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// Drawer contains the Draw method.
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type Drawer interface {
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// Draw aligns r.Min in dst with sp in src and then replaces the
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// rectangle r in dst with the result of drawing src on dst.
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Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point)
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}
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// FloydSteinberg is a Drawer that is the Src Op with Floyd-Steinberg error
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// diffusion.
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var FloydSteinberg Drawer = floydSteinberg{}
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type floydSteinberg struct{}
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func (floydSteinberg) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point) {
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clip(dst, &r, src, &sp, nil, nil)
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if r.Empty() {
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return
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}
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drawPaletted(dst, r, src, sp, true)
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}
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// clip clips r against each image's bounds (after translating into the
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// destination image's coordinate space) and shifts the points sp and mp by
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// the same amount as the change in r.Min.
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func clip(dst Image, r *image.Rectangle, src image.Image, sp *image.Point, mask image.Image, mp *image.Point) {
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orig := r.Min
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*r = r.Intersect(dst.Bounds())
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*r = r.Intersect(src.Bounds().Add(orig.Sub(*sp)))
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if mask != nil {
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*r = r.Intersect(mask.Bounds().Add(orig.Sub(*mp)))
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}
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dx := r.Min.X - orig.X
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dy := r.Min.Y - orig.Y
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if dx == 0 && dy == 0 {
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return
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}
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sp.X += dx
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sp.Y += dy
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if mp != nil {
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mp.X += dx
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mp.Y += dy
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}
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}
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func processBackward(dst Image, r image.Rectangle, src image.Image, sp image.Point) bool {
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return image.Image(dst) == src &&
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r.Overlaps(r.Add(sp.Sub(r.Min))) &&
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(sp.Y < r.Min.Y || (sp.Y == r.Min.Y && sp.X < r.Min.X))
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}
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// Draw calls DrawMask with a nil mask.
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func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op) {
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DrawMask(dst, r, src, sp, nil, image.Point{}, op)
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}
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// DrawMask aligns r.Min in dst with sp in src and mp in mask and then replaces the rectangle r
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// in dst with the result of a Porter-Duff composition. A nil mask is treated as opaque.
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func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
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clip(dst, &r, src, &sp, mask, &mp)
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if r.Empty() {
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return
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}
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// Fast paths for special cases. If none of them apply, then we fall back to a general but slow implementation.
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switch dst0 := dst.(type) {
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case *image.RGBA:
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if op == Over {
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if mask == nil {
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switch src0 := src.(type) {
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case *image.Uniform:
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drawFillOver(dst0, r, src0)
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return
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case *image.RGBA:
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drawCopyOver(dst0, r, src0, sp)
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return
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case *image.NRGBA:
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drawNRGBAOver(dst0, r, src0, sp)
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return
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case *image.YCbCr:
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// An image.YCbCr is always fully opaque, and so if the
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// mask is nil (i.e. fully opaque) then the op is
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// effectively always Src. Similarly for image.Gray and
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// image.CMYK.
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if imageutil.DrawYCbCr(dst0, r, src0, sp) {
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return
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}
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case *image.Gray:
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drawGray(dst0, r, src0, sp)
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return
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case *image.CMYK:
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drawCMYK(dst0, r, src0, sp)
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return
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}
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} else if mask0, ok := mask.(*image.Alpha); ok {
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switch src0 := src.(type) {
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case *image.Uniform:
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drawGlyphOver(dst0, r, src0, mask0, mp)
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return
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}
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}
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} else {
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if mask == nil {
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switch src0 := src.(type) {
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case *image.Uniform:
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drawFillSrc(dst0, r, src0)
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return
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case *image.RGBA:
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drawCopySrc(dst0, r, src0, sp)
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return
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case *image.NRGBA:
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drawNRGBASrc(dst0, r, src0, sp)
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return
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case *image.YCbCr:
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if imageutil.DrawYCbCr(dst0, r, src0, sp) {
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return
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}
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case *image.Gray:
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drawGray(dst0, r, src0, sp)
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return
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case *image.CMYK:
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drawCMYK(dst0, r, src0, sp)
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return
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}
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}
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}
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drawRGBA(dst0, r, src, sp, mask, mp, op)
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return
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case *image.Paletted:
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if op == Src && mask == nil && !processBackward(dst, r, src, sp) {
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drawPaletted(dst0, r, src, sp, false)
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return
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}
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}
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x0, x1, dx := r.Min.X, r.Max.X, 1
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y0, y1, dy := r.Min.Y, r.Max.Y, 1
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if processBackward(dst, r, src, sp) {
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x0, x1, dx = x1-1, x0-1, -1
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y0, y1, dy = y1-1, y0-1, -1
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}
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var out color.RGBA64
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sy := sp.Y + y0 - r.Min.Y
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my := mp.Y + y0 - r.Min.Y
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for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
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sx := sp.X + x0 - r.Min.X
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mx := mp.X + x0 - r.Min.X
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for x := x0; x != x1; x, sx, mx = x+dx, sx+dx, mx+dx {
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ma := uint32(m)
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if mask != nil {
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_, _, _, ma = mask.At(mx, my).RGBA()
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}
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switch {
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case ma == 0:
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if op == Over {
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// No-op.
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} else {
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dst.Set(x, y, color.Transparent)
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}
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case ma == m && op == Src:
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dst.Set(x, y, src.At(sx, sy))
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default:
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sr, sg, sb, sa := src.At(sx, sy).RGBA()
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if op == Over {
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dr, dg, db, da := dst.At(x, y).RGBA()
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a := m - (sa * ma / m)
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out.R = uint16((dr*a + sr*ma) / m)
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out.G = uint16((dg*a + sg*ma) / m)
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out.B = uint16((db*a + sb*ma) / m)
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out.A = uint16((da*a + sa*ma) / m)
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} else {
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out.R = uint16(sr * ma / m)
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out.G = uint16(sg * ma / m)
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out.B = uint16(sb * ma / m)
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out.A = uint16(sa * ma / m)
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}
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// The third argument is &out instead of out (and out is
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// declared outside of the inner loop) to avoid the implicit
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// conversion to color.Color here allocating memory in the
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// inner loop if sizeof(color.RGBA64) > sizeof(uintptr).
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dst.Set(x, y, &out)
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}
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}
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}
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}
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func drawFillOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform) {
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sr, sg, sb, sa := src.RGBA()
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// The 0x101 is here for the same reason as in drawRGBA.
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a := (m - sa) * 0x101
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i0 := dst.PixOffset(r.Min.X, r.Min.Y)
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i1 := i0 + r.Dx()*4
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for y := r.Min.Y; y != r.Max.Y; y++ {
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for i := i0; i < i1; i += 4 {
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dr := &dst.Pix[i+0]
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dg := &dst.Pix[i+1]
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db := &dst.Pix[i+2]
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da := &dst.Pix[i+3]
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*dr = uint8((uint32(*dr)*a/m + sr) >> 8)
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*dg = uint8((uint32(*dg)*a/m + sg) >> 8)
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*db = uint8((uint32(*db)*a/m + sb) >> 8)
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*da = uint8((uint32(*da)*a/m + sa) >> 8)
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}
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i0 += dst.Stride
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i1 += dst.Stride
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}
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}
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func drawFillSrc(dst *image.RGBA, r image.Rectangle, src *image.Uniform) {
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sr, sg, sb, sa := src.RGBA()
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sr8 := uint8(sr >> 8)
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sg8 := uint8(sg >> 8)
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sb8 := uint8(sb >> 8)
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sa8 := uint8(sa >> 8)
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// The built-in copy function is faster than a straightforward for loop to fill the destination with
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// the color, but copy requires a slice source. We therefore use a for loop to fill the first row, and
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// then use the first row as the slice source for the remaining rows.
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i0 := dst.PixOffset(r.Min.X, r.Min.Y)
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i1 := i0 + r.Dx()*4
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for i := i0; i < i1; i += 4 {
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dst.Pix[i+0] = sr8
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dst.Pix[i+1] = sg8
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dst.Pix[i+2] = sb8
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dst.Pix[i+3] = sa8
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}
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firstRow := dst.Pix[i0:i1]
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for y := r.Min.Y + 1; y < r.Max.Y; y++ {
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i0 += dst.Stride
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i1 += dst.Stride
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copy(dst.Pix[i0:i1], firstRow)
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}
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}
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func drawCopyOver(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
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dx, dy := r.Dx(), r.Dy()
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d0 := dst.PixOffset(r.Min.X, r.Min.Y)
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s0 := src.PixOffset(sp.X, sp.Y)
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var (
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ddelta, sdelta int
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i0, i1, idelta int
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)
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if r.Min.Y < sp.Y || r.Min.Y == sp.Y && r.Min.X <= sp.X {
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ddelta = dst.Stride
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sdelta = src.Stride
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i0, i1, idelta = 0, dx*4, +4
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} else {
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// If the source start point is higher than the destination start point, or equal height but to the left,
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// then we compose the rows in right-to-left, bottom-up order instead of left-to-right, top-down.
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d0 += (dy - 1) * dst.Stride
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s0 += (dy - 1) * src.Stride
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ddelta = -dst.Stride
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sdelta = -src.Stride
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i0, i1, idelta = (dx-1)*4, -4, -4
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}
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for ; dy > 0; dy-- {
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dpix := dst.Pix[d0:]
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spix := src.Pix[s0:]
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for i := i0; i != i1; i += idelta {
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sr := uint32(spix[i+0]) * 0x101
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sg := uint32(spix[i+1]) * 0x101
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sb := uint32(spix[i+2]) * 0x101
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sa := uint32(spix[i+3]) * 0x101
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dr := &dpix[i+0]
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dg := &dpix[i+1]
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db := &dpix[i+2]
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da := &dpix[i+3]
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// The 0x101 is here for the same reason as in drawRGBA.
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a := (m - sa) * 0x101
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*dr = uint8((uint32(*dr)*a/m + sr) >> 8)
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*dg = uint8((uint32(*dg)*a/m + sg) >> 8)
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*db = uint8((uint32(*db)*a/m + sb) >> 8)
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*da = uint8((uint32(*da)*a/m + sa) >> 8)
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}
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d0 += ddelta
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s0 += sdelta
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}
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}
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func drawCopySrc(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
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n, dy := 4*r.Dx(), r.Dy()
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d0 := dst.PixOffset(r.Min.X, r.Min.Y)
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s0 := src.PixOffset(sp.X, sp.Y)
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var ddelta, sdelta int
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if r.Min.Y <= sp.Y {
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ddelta = dst.Stride
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sdelta = src.Stride
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} else {
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// If the source start point is higher than the destination start
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// point, then we compose the rows in bottom-up order instead of
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// top-down. Unlike the drawCopyOver function, we don't have to check
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// the x coordinates because the built-in copy function can handle
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// overlapping slices.
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d0 += (dy - 1) * dst.Stride
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s0 += (dy - 1) * src.Stride
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ddelta = -dst.Stride
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sdelta = -src.Stride
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}
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for ; dy > 0; dy-- {
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copy(dst.Pix[d0:d0+n], src.Pix[s0:s0+n])
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d0 += ddelta
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s0 += sdelta
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}
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}
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func drawNRGBAOver(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) {
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i0 := (r.Min.X - dst.Rect.Min.X) * 4
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i1 := (r.Max.X - dst.Rect.Min.X) * 4
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si0 := (sp.X - src.Rect.Min.X) * 4
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yMax := r.Max.Y - dst.Rect.Min.Y
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y := r.Min.Y - dst.Rect.Min.Y
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sy := sp.Y - src.Rect.Min.Y
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for ; y != yMax; y, sy = y+1, sy+1 {
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dpix := dst.Pix[y*dst.Stride:]
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spix := src.Pix[sy*src.Stride:]
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for i, si := i0, si0; i < i1; i, si = i+4, si+4 {
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// Convert from non-premultiplied color to pre-multiplied color.
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sa := uint32(spix[si+3]) * 0x101
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sr := uint32(spix[si+0]) * sa / 0xff
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sg := uint32(spix[si+1]) * sa / 0xff
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sb := uint32(spix[si+2]) * sa / 0xff
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dr := uint32(dpix[i+0])
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dg := uint32(dpix[i+1])
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db := uint32(dpix[i+2])
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da := uint32(dpix[i+3])
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// The 0x101 is here for the same reason as in drawRGBA.
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a := (m - sa) * 0x101
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dpix[i+0] = uint8((dr*a/m + sr) >> 8)
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dpix[i+1] = uint8((dg*a/m + sg) >> 8)
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dpix[i+2] = uint8((db*a/m + sb) >> 8)
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dpix[i+3] = uint8((da*a/m + sa) >> 8)
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}
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}
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}
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func drawNRGBASrc(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) {
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i0 := (r.Min.X - dst.Rect.Min.X) * 4
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i1 := (r.Max.X - dst.Rect.Min.X) * 4
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si0 := (sp.X - src.Rect.Min.X) * 4
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yMax := r.Max.Y - dst.Rect.Min.Y
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y := r.Min.Y - dst.Rect.Min.Y
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sy := sp.Y - src.Rect.Min.Y
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for ; y != yMax; y, sy = y+1, sy+1 {
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dpix := dst.Pix[y*dst.Stride:]
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spix := src.Pix[sy*src.Stride:]
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for i, si := i0, si0; i < i1; i, si = i+4, si+4 {
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// Convert from non-premultiplied color to pre-multiplied color.
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sa := uint32(spix[si+3]) * 0x101
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sr := uint32(spix[si+0]) * sa / 0xff
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sg := uint32(spix[si+1]) * sa / 0xff
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sb := uint32(spix[si+2]) * sa / 0xff
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dpix[i+0] = uint8(sr >> 8)
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dpix[i+1] = uint8(sg >> 8)
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dpix[i+2] = uint8(sb >> 8)
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dpix[i+3] = uint8(sa >> 8)
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}
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}
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}
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func drawGray(dst *image.RGBA, r image.Rectangle, src *image.Gray, sp image.Point) {
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i0 := (r.Min.X - dst.Rect.Min.X) * 4
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i1 := (r.Max.X - dst.Rect.Min.X) * 4
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si0 := (sp.X - src.Rect.Min.X) * 1
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yMax := r.Max.Y - dst.Rect.Min.Y
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y := r.Min.Y - dst.Rect.Min.Y
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sy := sp.Y - src.Rect.Min.Y
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for ; y != yMax; y, sy = y+1, sy+1 {
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dpix := dst.Pix[y*dst.Stride:]
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spix := src.Pix[sy*src.Stride:]
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for i, si := i0, si0; i < i1; i, si = i+4, si+1 {
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p := spix[si]
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dpix[i+0] = p
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dpix[i+1] = p
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dpix[i+2] = p
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dpix[i+3] = 255
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}
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}
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}
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func drawCMYK(dst *image.RGBA, r image.Rectangle, src *image.CMYK, sp image.Point) {
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i0 := (r.Min.X - dst.Rect.Min.X) * 4
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i1 := (r.Max.X - dst.Rect.Min.X) * 4
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si0 := (sp.X - src.Rect.Min.X) * 4
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yMax := r.Max.Y - dst.Rect.Min.Y
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y := r.Min.Y - dst.Rect.Min.Y
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|
sy := sp.Y - src.Rect.Min.Y
|
|
for ; y != yMax; y, sy = y+1, sy+1 {
|
|
dpix := dst.Pix[y*dst.Stride:]
|
|
spix := src.Pix[sy*src.Stride:]
|
|
|
|
for i, si := i0, si0; i < i1; i, si = i+4, si+4 {
|
|
dpix[i+0], dpix[i+1], dpix[i+2] =
|
|
color.CMYKToRGB(spix[si+0], spix[si+1], spix[si+2], spix[si+3])
|
|
dpix[i+3] = 255
|
|
}
|
|
}
|
|
}
|
|
|
|
func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform, mask *image.Alpha, mp image.Point) {
|
|
i0 := dst.PixOffset(r.Min.X, r.Min.Y)
|
|
i1 := i0 + r.Dx()*4
|
|
mi0 := mask.PixOffset(mp.X, mp.Y)
|
|
sr, sg, sb, sa := src.RGBA()
|
|
for y, my := r.Min.Y, mp.Y; y != r.Max.Y; y, my = y+1, my+1 {
|
|
for i, mi := i0, mi0; i < i1; i, mi = i+4, mi+1 {
|
|
ma := uint32(mask.Pix[mi])
|
|
if ma == 0 {
|
|
continue
|
|
}
|
|
ma |= ma << 8
|
|
|
|
dr := &dst.Pix[i+0]
|
|
dg := &dst.Pix[i+1]
|
|
db := &dst.Pix[i+2]
|
|
da := &dst.Pix[i+3]
|
|
|
|
// The 0x101 is here for the same reason as in drawRGBA.
|
|
a := (m - (sa * ma / m)) * 0x101
|
|
|
|
*dr = uint8((uint32(*dr)*a + sr*ma) / m >> 8)
|
|
*dg = uint8((uint32(*dg)*a + sg*ma) / m >> 8)
|
|
*db = uint8((uint32(*db)*a + sb*ma) / m >> 8)
|
|
*da = uint8((uint32(*da)*a + sa*ma) / m >> 8)
|
|
}
|
|
i0 += dst.Stride
|
|
i1 += dst.Stride
|
|
mi0 += mask.Stride
|
|
}
|
|
}
|
|
|
|
func drawRGBA(dst *image.RGBA, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
|
|
x0, x1, dx := r.Min.X, r.Max.X, 1
|
|
y0, y1, dy := r.Min.Y, r.Max.Y, 1
|
|
if image.Image(dst) == src && r.Overlaps(r.Add(sp.Sub(r.Min))) {
|
|
if sp.Y < r.Min.Y || sp.Y == r.Min.Y && sp.X < r.Min.X {
|
|
x0, x1, dx = x1-1, x0-1, -1
|
|
y0, y1, dy = y1-1, y0-1, -1
|
|
}
|
|
}
|
|
|
|
sy := sp.Y + y0 - r.Min.Y
|
|
my := mp.Y + y0 - r.Min.Y
|
|
sx0 := sp.X + x0 - r.Min.X
|
|
mx0 := mp.X + x0 - r.Min.X
|
|
sx1 := sx0 + (x1 - x0)
|
|
i0 := dst.PixOffset(x0, y0)
|
|
di := dx * 4
|
|
for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
|
|
for i, sx, mx := i0, sx0, mx0; sx != sx1; i, sx, mx = i+di, sx+dx, mx+dx {
|
|
ma := uint32(m)
|
|
if mask != nil {
|
|
_, _, _, ma = mask.At(mx, my).RGBA()
|
|
}
|
|
sr, sg, sb, sa := src.At(sx, sy).RGBA()
|
|
if op == Over {
|
|
dr := uint32(dst.Pix[i+0])
|
|
dg := uint32(dst.Pix[i+1])
|
|
db := uint32(dst.Pix[i+2])
|
|
da := uint32(dst.Pix[i+3])
|
|
|
|
// dr, dg, db and da are all 8-bit color at the moment, ranging in [0,255].
|
|
// We work in 16-bit color, and so would normally do:
|
|
// dr |= dr << 8
|
|
// and similarly for dg, db and da, but instead we multiply a
|
|
// (which is a 16-bit color, ranging in [0,65535]) by 0x101.
|
|
// This yields the same result, but is fewer arithmetic operations.
|
|
a := (m - (sa * ma / m)) * 0x101
|
|
|
|
dst.Pix[i+0] = uint8((dr*a + sr*ma) / m >> 8)
|
|
dst.Pix[i+1] = uint8((dg*a + sg*ma) / m >> 8)
|
|
dst.Pix[i+2] = uint8((db*a + sb*ma) / m >> 8)
|
|
dst.Pix[i+3] = uint8((da*a + sa*ma) / m >> 8)
|
|
|
|
} else {
|
|
dst.Pix[i+0] = uint8(sr * ma / m >> 8)
|
|
dst.Pix[i+1] = uint8(sg * ma / m >> 8)
|
|
dst.Pix[i+2] = uint8(sb * ma / m >> 8)
|
|
dst.Pix[i+3] = uint8(sa * ma / m >> 8)
|
|
}
|
|
}
|
|
i0 += dy * dst.Stride
|
|
}
|
|
}
|
|
|
|
// clamp clamps i to the interval [0, 0xffff].
|
|
func clamp(i int32) int32 {
|
|
if i < 0 {
|
|
return 0
|
|
}
|
|
if i > 0xffff {
|
|
return 0xffff
|
|
}
|
|
return i
|
|
}
|
|
|
|
// sqDiff returns the squared-difference of x and y, shifted by 2 so that
|
|
// adding four of those won't overflow a uint32.
|
|
//
|
|
// x and y are both assumed to be in the range [0, 0xffff].
|
|
func sqDiff(x, y int32) uint32 {
|
|
var d uint32
|
|
if x > y {
|
|
d = uint32(x - y)
|
|
} else {
|
|
d = uint32(y - x)
|
|
}
|
|
return (d * d) >> 2
|
|
}
|
|
|
|
func drawPaletted(dst Image, r image.Rectangle, src image.Image, sp image.Point, floydSteinberg bool) {
|
|
// TODO(nigeltao): handle the case where the dst and src overlap.
|
|
// Does it even make sense to try and do Floyd-Steinberg whilst
|
|
// walking the image backward (right-to-left bottom-to-top)?
|
|
|
|
// If dst is an *image.Paletted, we have a fast path for dst.Set and
|
|
// dst.At. The dst.Set equivalent is a batch version of the algorithm
|
|
// used by color.Palette's Index method in image/color/color.go, plus
|
|
// optional Floyd-Steinberg error diffusion.
|
|
palette, pix, stride := [][4]int32(nil), []byte(nil), 0
|
|
if p, ok := dst.(*image.Paletted); ok {
|
|
palette = make([][4]int32, len(p.Palette))
|
|
for i, col := range p.Palette {
|
|
r, g, b, a := col.RGBA()
|
|
palette[i][0] = int32(r)
|
|
palette[i][1] = int32(g)
|
|
palette[i][2] = int32(b)
|
|
palette[i][3] = int32(a)
|
|
}
|
|
pix, stride = p.Pix[p.PixOffset(r.Min.X, r.Min.Y):], p.Stride
|
|
}
|
|
|
|
// quantErrorCurr and quantErrorNext are the Floyd-Steinberg quantization
|
|
// errors that have been propagated to the pixels in the current and next
|
|
// rows. The +2 simplifies calculation near the edges.
|
|
var quantErrorCurr, quantErrorNext [][4]int32
|
|
if floydSteinberg {
|
|
quantErrorCurr = make([][4]int32, r.Dx()+2)
|
|
quantErrorNext = make([][4]int32, r.Dx()+2)
|
|
}
|
|
|
|
// Loop over each source pixel.
|
|
out := color.RGBA64{A: 0xffff}
|
|
for y := 0; y != r.Dy(); y++ {
|
|
for x := 0; x != r.Dx(); x++ {
|
|
// er, eg and eb are the pixel's R,G,B values plus the
|
|
// optional Floyd-Steinberg error.
|
|
sr, sg, sb, sa := src.At(sp.X+x, sp.Y+y).RGBA()
|
|
er, eg, eb, ea := int32(sr), int32(sg), int32(sb), int32(sa)
|
|
if floydSteinberg {
|
|
er = clamp(er + quantErrorCurr[x+1][0]/16)
|
|
eg = clamp(eg + quantErrorCurr[x+1][1]/16)
|
|
eb = clamp(eb + quantErrorCurr[x+1][2]/16)
|
|
ea = clamp(ea + quantErrorCurr[x+1][3]/16)
|
|
}
|
|
|
|
if palette != nil {
|
|
// Find the closest palette color in Euclidean R,G,B,A space:
|
|
// the one that minimizes sum-squared-difference.
|
|
// TODO(nigeltao): consider smarter algorithms.
|
|
bestIndex, bestSum := 0, uint32(1<<32-1)
|
|
for index, p := range palette {
|
|
sum := sqDiff(er, p[0]) + sqDiff(eg, p[1]) + sqDiff(eb, p[2]) + sqDiff(ea, p[3])
|
|
if sum < bestSum {
|
|
bestIndex, bestSum = index, sum
|
|
if sum == 0 {
|
|
break
|
|
}
|
|
}
|
|
}
|
|
pix[y*stride+x] = byte(bestIndex)
|
|
|
|
if !floydSteinberg {
|
|
continue
|
|
}
|
|
er -= palette[bestIndex][0]
|
|
eg -= palette[bestIndex][1]
|
|
eb -= palette[bestIndex][2]
|
|
ea -= palette[bestIndex][3]
|
|
|
|
} else {
|
|
out.R = uint16(er)
|
|
out.G = uint16(eg)
|
|
out.B = uint16(eb)
|
|
out.A = uint16(ea)
|
|
// The third argument is &out instead of out (and out is
|
|
// declared outside of the inner loop) to avoid the implicit
|
|
// conversion to color.Color here allocating memory in the
|
|
// inner loop if sizeof(color.RGBA64) > sizeof(uintptr).
|
|
dst.Set(r.Min.X+x, r.Min.Y+y, &out)
|
|
|
|
if !floydSteinberg {
|
|
continue
|
|
}
|
|
sr, sg, sb, sa = dst.At(r.Min.X+x, r.Min.Y+y).RGBA()
|
|
er -= int32(sr)
|
|
eg -= int32(sg)
|
|
eb -= int32(sb)
|
|
ea -= int32(sa)
|
|
}
|
|
|
|
// Propagate the Floyd-Steinberg quantization error.
|
|
quantErrorNext[x+0][0] += er * 3
|
|
quantErrorNext[x+0][1] += eg * 3
|
|
quantErrorNext[x+0][2] += eb * 3
|
|
quantErrorNext[x+0][3] += ea * 3
|
|
quantErrorNext[x+1][0] += er * 5
|
|
quantErrorNext[x+1][1] += eg * 5
|
|
quantErrorNext[x+1][2] += eb * 5
|
|
quantErrorNext[x+1][3] += ea * 5
|
|
quantErrorNext[x+2][0] += er * 1
|
|
quantErrorNext[x+2][1] += eg * 1
|
|
quantErrorNext[x+2][2] += eb * 1
|
|
quantErrorNext[x+2][3] += ea * 1
|
|
quantErrorCurr[x+2][0] += er * 7
|
|
quantErrorCurr[x+2][1] += eg * 7
|
|
quantErrorCurr[x+2][2] += eb * 7
|
|
quantErrorCurr[x+2][3] += ea * 7
|
|
}
|
|
|
|
// Recycle the quantization error buffers.
|
|
if floydSteinberg {
|
|
quantErrorCurr, quantErrorNext = quantErrorNext, quantErrorCurr
|
|
for i := range quantErrorNext {
|
|
quantErrorNext[i] = [4]int32{}
|
|
}
|
|
}
|
|
}
|
|
}
|