feat: splitsprite 增加白底移除、固定网格拆分与帧居中功能
- 新增 RemoveWhiteBg：纯白色背景(#FFFFFF)像素半透明化 - 新增 fixedGridSplit：GridRows×GridCols 固定网格拆分 - 新增 CenterAlign：帧内容居中对齐，确保人物不跳帧 - Options 新增 WhiteBg/GridRows/GridCols/GridPadding/CenterAlign - 默认模式从绿幕切换为白底 - 新增 tools/test_prompt_to_gif.go 端到端测试脚本 - .gitignore 忽略 test_output 目录
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@@ -1,6 +1,6 @@
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// Package splitsprite provides PNG sprite sheet splitting utilities.
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//
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// Pipeline: green screen removal → projection-based gap detection →
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// Pipeline: white/green background removal → projection-based gap detection →
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// split into tiles → filter out low-fill tiles → trim transparent edges.
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package splitsprite
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@@ -15,11 +15,23 @@ import (
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// Options configures the sprite sheet splitting pipeline.
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type Options struct {
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// WhiteBg enables white background removal.
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WhiteBg bool
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// WhiteThreshold is the max distance from pure white (0–255, default 40).
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WhiteThreshold uint8
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// GreenScreen enables green background removal.
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GreenScreen bool
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// GreenTolerance controls how aggressively green pixels are removed (0–1, default 0.2).
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GreenTolerance float64
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// GridRows / GridCols enable fixed-grid splitting (overrides projection detection).
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// When >0, the image is divided equally into Rows×Cols cells.
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GridRows int
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GridCols int
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// GridPadding is the gap between cells in pixels (default 2).
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GridPadding int
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// GapThreshold is the max fraction of non-transparent pixels a row/column
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// can have to be considered a gap (0–1, default 0.03).
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GapThreshold float64
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@@ -32,12 +44,27 @@ type Options struct {
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// Trim removes transparent borders from output tiles.
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Trim bool
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// CenterAlign centers content across all frames so characters stay in place.
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// All output frames get the same dimensions with content centered.
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CenterAlign bool
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// OutW / OutH specify the output tile size (0 = keep original).
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OutW, OutH int
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}
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// DefaultOptions returns sensible default splitting options.
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// DefaultOptions returns sensible default splitting options (white background mode).
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func DefaultOptions() *Options {
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return &Options{
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WhiteBg: true,
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WhiteThreshold: 40,
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GapThreshold: 0.03,
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MinGapWidth: 2,
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MinFillRatio: 0.3,
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Trim: true,
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}
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}
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// DefaultGreenOptions returns options tuned for green screen sprite sheets.
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func DefaultGreenOptions() *Options {
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return &Options{
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GreenScreen: true,
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GreenTolerance: 0.2,
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@@ -49,7 +76,8 @@ func DefaultOptions() *Options {
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}
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// Process splits a sprite sheet image into individual cleaned tile images.
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// It runs the full pipeline: green screen removal → split → trim → resize.
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// It runs the full pipeline: background removal → split → trim → resize.
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// When GridRows/GridCols > 0, fixed-grid splitting is used instead of projection detection.
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func Process(img image.Image, opts *Options) ([]image.Image, error) {
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if opts == nil {
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opts = DefaultOptions()
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@@ -57,13 +85,20 @@ func Process(img image.Image, opts *Options) ([]image.Image, error) {
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src := toRGBA(img)
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if opts.GreenScreen {
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if opts.WhiteBg {
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src = removeWhiteBg(src, opts.WhiteThreshold)
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} else if opts.GreenScreen {
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src = removeGreenScreen(src, opts.GreenTolerance)
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}
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tiles := projectionSplit(src, opts.GapThreshold, opts.MinGapWidth, opts.MinFillRatio)
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var tiles []tile
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if opts.GridRows > 0 && opts.GridCols > 0 {
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tiles = fixedGridSplit(src, opts.GridRows, opts.GridCols, opts.GridPadding, opts.MinFillRatio)
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} else {
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tiles = projectionSplit(src, opts.GapThreshold, opts.MinGapWidth, opts.MinFillRatio)
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}
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if len(tiles) == 0 {
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return nil, fmt.Errorf("no tiles detected — try lowering GapThreshold or adjusting GreenTolerance")
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return nil, fmt.Errorf("no tiles detected — try lowering GapThreshold or setting GridRows/GridCols")
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}
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results := make([]image.Image, len(tiles))
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@@ -79,9 +114,98 @@ func Process(img image.Image, opts *Options) ([]image.Image, error) {
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}
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results[i] = sub
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}
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if opts.CenterAlign && len(results) > 1 {
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results = alignCenter(results)
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}
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return results, nil
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}
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// RemoveWhiteBg removes near-white background pixels, making them transparent.
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func RemoveWhiteBg(img image.Image, threshold uint8) image.Image {
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return removeWhiteBg(toRGBA(img), threshold)
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}
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// CenterFrames centers the content of each frame within a uniform canvas so
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// characters stay in place across frames.
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func CenterFrames(frames []image.Image) []image.Image {
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return alignCenter(frames)
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}
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// alignCenter finds the content bounding box per frame, computes the max
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// dimensions, then pads each frame so content is centered uniformly.
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func alignCenter(frames []image.Image) []image.Image {
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type contentBox struct {
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minX, minY, maxX, maxY int
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}
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boxes := make([]contentBox, len(frames))
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maxW, maxH := 0, 0
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for i, f := range frames {
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b := f.Bounds()
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minX, minY := b.Max.X, b.Max.Y
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maxX, maxY := b.Min.X, b.Min.Y
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hasContent := false
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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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_, _, _, a := f.At(x, y).RGBA()
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if a > 0 {
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hasContent = true
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if x < minX {
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minX = x
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}
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if x > maxX {
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maxX = x
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}
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if y < minY {
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minY = y
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}
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if y > maxY {
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maxY = y
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}
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}
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}
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}
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if !hasContent {
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boxes[i] = contentBox{0, 0, b.Dx(), b.Dy()}
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} else {
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boxes[i] = contentBox{minX, minY, maxX, maxY}
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}
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w := boxes[i].maxX - boxes[i].minX + 1
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h := boxes[i].maxY - boxes[i].minY + 1
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if w > maxW {
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maxW = w
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}
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if h > maxH {
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maxH = h
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}
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}
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// Pad by 10% to avoid edge cropping
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maxW = maxW * 11 / 10
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maxH = maxH * 11 / 10
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out := make([]image.Image, len(frames))
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for i, f := range frames {
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cb := boxes[i]
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cw := cb.maxX - cb.minX + 1
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ch := cb.maxY - cb.minY + 1
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ox := (maxW - cw) / 2
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oy := (maxH - ch) / 2
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canvas := image.NewRGBA(image.Rect(0, 0, maxW, maxH))
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draw.Draw(canvas,
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image.Rect(ox, oy, ox+cw, oy+ch),
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f,
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image.Point{cb.minX, cb.minY},
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draw.Src,
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)
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out[i] = canvas
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}
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return out
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}
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// RemoveGreenScreen removes green-dominant background pixels, making them transparent.
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func RemoveGreenScreen(img image.Image, tol float64) image.Image {
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return removeGreenScreen(toRGBA(img), tol)
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@@ -105,6 +229,34 @@ type tile struct {
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x, y, w, h int
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}
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// removeWhiteBg removes pixels close to pure white (R,G,B all above threshold).
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func removeWhiteBg(rgba *image.RGBA, threshold uint8) *image.RGBA {
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if threshold == 0 {
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threshold = 40
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}
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b := rgba.Bounds()
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dst := image.NewRGBA(b)
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draw.Draw(dst, b, rgba, b.Min, draw.Src)
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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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r, g, bl, a := rgba.At(x, y).RGBA()
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if a == 0 {
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continue
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}
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r8, g8, b8 := uint8(r>>8), uint8(g>>8), uint8(bl>>8)
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// Pixel is "white" when all channels are near 255
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if int(255-r8) < int(threshold) && int(255-g8) < int(threshold) && int(255-b8) < int(threshold) {
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// Calculate alpha: closer to white = more transparent
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dist := max(int(255-r8), max(int(255-g8), int(255-b8)))
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alpha := float64(dist) / float64(threshold)
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dst.SetRGBA(x, y, color.RGBA{R: r8, G: g8, B: b8, A: uint8(alpha * 255)})
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}
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}
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}
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return dst
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}
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func removeGreenScreen(rgba *image.RGBA, tol float64) *image.RGBA {
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b := rgba.Bounds()
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dst := image.NewRGBA(b)
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@@ -132,6 +284,36 @@ func removeGreenScreen(rgba *image.RGBA, tol float64) *image.RGBA {
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return dst
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}
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// fixedGridSplit divides the image into Rows×Cols equally-sized cells,
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// accounting for a fixed padding between cells.
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func fixedGridSplit(rgba *image.RGBA, rows, cols, padding int, minFill float64) []tile {
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b := rgba.Bounds()
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W, H := b.Dx(), b.Dy()
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if padding < 0 {
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padding = 0
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}
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totalPadW := padding * (cols + 1)
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totalPadH := padding * (rows + 1)
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cellW := (W - totalPadW) / cols
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cellH := (H - totalPadH) / rows
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if cellW <= 0 || cellH <= 0 {
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return nil
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}
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var tiles []tile
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for r := 0; r < rows; r++ {
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for c := 0; c < cols; c++ {
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x := padding + c*(cellW+padding)
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y := padding + r*(cellH+padding)
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if tileFillRatio(rgba, x, y, cellW, cellH) >= minFill {
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tiles = append(tiles, tile{x: x, y: y, w: cellW, h: cellH})
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}
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}
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}
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return tiles
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}
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func projectionSplit(rgba *image.RGBA, gapThreshold float64, minGap int, minFill float64) []tile {
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bounds := rgba.Bounds()
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W, H := bounds.Dx(), bounds.Dy()
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