275 lines
6.4 KiB
Go
275 lines
6.4 KiB
Go
// Copyright 2011 The Graphics-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 convolve
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import (
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"errors"
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"fmt"
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"image"
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"image/draw"
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"math"
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)
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// clamp clamps x to the range [x0, x1].
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func clamp(x, x0, x1 float64) float64 {
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if x < x0 {
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return x0
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}
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if x > x1 {
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return x1
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}
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return x
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}
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// Kernel is a square matrix that defines a convolution.
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type Kernel interface {
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// Weights returns the square matrix of weights in row major order.
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Weights() []float64
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}
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// SeparableKernel is a linearly separable, square convolution kernel.
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// X and Y are the per-axis weights. Each slice must be the same length, and
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// have an odd length. The middle element of each slice is the weight for the
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// central pixel. For example, the horizontal Sobel kernel is:
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// sobelX := &SeparableKernel{
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// X: []float64{-1, 0, +1},
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// Y: []float64{1, 2, 1},
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// }
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type SeparableKernel struct {
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X, Y []float64
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}
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func (k *SeparableKernel) Weights() []float64 {
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n := len(k.X)
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w := make([]float64, n*n)
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for y := 0; y < n; y++ {
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for x := 0; x < n; x++ {
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w[y*n+x] = k.X[x] * k.Y[y]
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}
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}
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return w
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}
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// fullKernel is a square convolution kernel.
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type fullKernel []float64
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func (k fullKernel) Weights() []float64 { return k }
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func kernelSize(w []float64) (size int, err error) {
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size = int(math.Sqrt(float64(len(w))))
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if size*size != len(w) {
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return 0, errors.New("graphics: kernel is not square")
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}
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if size%2 != 1 {
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return 0, errors.New("graphics: kernel size is not odd")
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}
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return size, nil
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}
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// NewKernel returns a square convolution kernel.
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func NewKernel(w []float64) (Kernel, error) {
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if _, err := kernelSize(w); err != nil {
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return nil, err
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}
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return fullKernel(w), nil
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}
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func convolveRGBASep(dst *image.RGBA, src image.Image, k *SeparableKernel) error {
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if len(k.X) != len(k.Y) {
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return fmt.Errorf("graphics: kernel not square (x %d, y %d)", len(k.X), len(k.Y))
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}
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if len(k.X)%2 != 1 {
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return fmt.Errorf("graphics: kernel length (%d) not odd", len(k.X))
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}
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radius := (len(k.X) - 1) / 2
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// buf holds the result of vertically blurring src.
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bounds := dst.Bounds()
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width, height := bounds.Dx(), bounds.Dy()
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buf := make([]float64, width*height*4)
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for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
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for x := bounds.Min.X; x < bounds.Max.X; x++ {
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var r, g, b, a float64
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// k0 is the kernel weight for the center pixel. This may be greater
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// than kernel[0], near the boundary of the source image, to avoid
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// vignetting.
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k0 := k.X[radius]
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// Add the pixels from above.
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for i := 1; i <= radius; i++ {
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f := k.Y[radius-i]
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if y-i < bounds.Min.Y {
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k0 += f
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} else {
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or, og, ob, oa := src.At(x, y-i).RGBA()
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r += float64(or>>8) * f
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g += float64(og>>8) * f
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b += float64(ob>>8) * f
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a += float64(oa>>8) * f
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}
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}
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// Add the pixels from below.
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for i := 1; i <= radius; i++ {
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f := k.Y[radius+i]
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if y+i >= bounds.Max.Y {
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k0 += f
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} else {
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or, og, ob, oa := src.At(x, y+i).RGBA()
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r += float64(or>>8) * f
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g += float64(og>>8) * f
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b += float64(ob>>8) * f
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a += float64(oa>>8) * f
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}
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}
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// Add the central pixel.
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or, og, ob, oa := src.At(x, y).RGBA()
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r += float64(or>>8) * k0
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g += float64(og>>8) * k0
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b += float64(ob>>8) * k0
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a += float64(oa>>8) * k0
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// Write to buf.
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o := (y-bounds.Min.Y)*width*4 + (x-bounds.Min.X)*4
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buf[o+0] = r
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buf[o+1] = g
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buf[o+2] = b
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buf[o+3] = a
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}
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}
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// dst holds the result of horizontally blurring buf.
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for y := 0; y < height; y++ {
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for x := 0; x < width; x++ {
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var r, g, b, a float64
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k0, off := k.X[radius], y*width*4+x*4
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// Add the pixels from the left.
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for i := 1; i <= radius; i++ {
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f := k.X[radius-i]
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if x-i < 0 {
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k0 += f
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} else {
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o := off - i*4
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r += buf[o+0] * f
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g += buf[o+1] * f
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b += buf[o+2] * f
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a += buf[o+3] * f
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}
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}
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// Add the pixels from the right.
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for i := 1; i <= radius; i++ {
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f := k.X[radius+i]
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if x+i >= width {
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k0 += f
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} else {
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o := off + i*4
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r += buf[o+0] * f
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g += buf[o+1] * f
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b += buf[o+2] * f
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a += buf[o+3] * f
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}
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}
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// Add the central pixel.
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r += buf[off+0] * k0
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g += buf[off+1] * k0
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b += buf[off+2] * k0
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a += buf[off+3] * k0
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// Write to dst, clamping to the range [0, 255].
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dstOff := (y-dst.Rect.Min.Y)*dst.Stride + (x-dst.Rect.Min.X)*4
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dst.Pix[dstOff+0] = uint8(clamp(r+0.5, 0, 255))
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dst.Pix[dstOff+1] = uint8(clamp(g+0.5, 0, 255))
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dst.Pix[dstOff+2] = uint8(clamp(b+0.5, 0, 255))
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dst.Pix[dstOff+3] = uint8(clamp(a+0.5, 0, 255))
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}
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}
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return nil
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}
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func convolveRGBA(dst *image.RGBA, src image.Image, k Kernel) error {
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b := dst.Bounds()
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bs := src.Bounds()
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w := k.Weights()
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size, err := kernelSize(w)
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if err != nil {
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return err
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}
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radius := (size - 1) / 2
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for y := b.Min.Y; y < b.Max.Y; y++ {
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for x := b.Min.X; x < b.Max.X; x++ {
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if !image.Pt(x, y).In(bs) {
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continue
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}
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var r, g, b, a, adj float64
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for cy := y - radius; cy <= y+radius; cy++ {
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for cx := x - radius; cx <= x+radius; cx++ {
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factor := w[(cy-y+radius)*size+cx-x+radius]
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if !image.Pt(cx, cy).In(bs) {
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adj += factor
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} else {
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sr, sg, sb, sa := src.At(cx, cy).RGBA()
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r += float64(sr>>8) * factor
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g += float64(sg>>8) * factor
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b += float64(sb>>8) * factor
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a += float64(sa>>8) * factor
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}
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}
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}
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if adj != 0 {
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sr, sg, sb, sa := src.At(x, y).RGBA()
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r += float64(sr>>8) * adj
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g += float64(sg>>8) * adj
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b += float64(sb>>8) * adj
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a += float64(sa>>8) * adj
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}
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off := (y-dst.Rect.Min.Y)*dst.Stride + (x-dst.Rect.Min.X)*4
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dst.Pix[off+0] = uint8(clamp(r+0.5, 0, 0xff))
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dst.Pix[off+1] = uint8(clamp(g+0.5, 0, 0xff))
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dst.Pix[off+2] = uint8(clamp(b+0.5, 0, 0xff))
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dst.Pix[off+3] = uint8(clamp(a+0.5, 0, 0xff))
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}
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}
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return nil
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}
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// Convolve produces dst by applying the convolution kernel k to src.
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func Convolve(dst draw.Image, src image.Image, k Kernel) (err error) {
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if dst == nil || src == nil || k == nil {
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return nil
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}
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b := dst.Bounds()
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dstRgba, ok := dst.(*image.RGBA)
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if !ok {
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dstRgba = image.NewRGBA(b)
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}
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switch k := k.(type) {
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case *SeparableKernel:
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err = convolveRGBASep(dstRgba, src, k)
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default:
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err = convolveRGBA(dstRgba, src, k)
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}
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if err != nil {
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return err
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}
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if !ok {
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draw.Draw(dst, b, dstRgba, b.Min, draw.Src)
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}
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return nil
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}
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