feat: 投影法波谷检测+白底硬切断+帧底部对齐+gifmaker透明GIF

- prompt_agent: 精灵表/瓦片集间隙从2-4px放宽到8-16px纯白
- splitsprite removeWhiteBg: dist<threshold/2直接A=0，消除半透明残留
- splitsprite findCuts: 波峰-波谷检测替代死阈值，归并原阈值回退
- splitsprite alignCenter: 全局画布底部对齐替代独立居中，人物不跳帧
- splitsprite MinFillRatio 调至0.14，MinGapWidth调至2
- 新增 pkg/gifmaker: 统一画布+透明索引0+DisposalBackground
- test_prompt_to_gif 改用gifmaker包

.gitignore

@@ -27,3 +27,4 @@ backend/main
 # Generated output
 generation/
 backend/test_output/
+backend/test_prompt_to_gif

backend/internal/service/prompt_agent.go

@@ -91,19 +91,20 @@ func buildMetaPrompt(in PromptAgentInput) string {
 	sb.WriteString("2. 使用专业术语，描述具体、可执行\n")
 	sb.WriteString("3. 风格一致，适合游戏资产管线\n")
 	sb.WriteString("4. 根据用户标签和描述，识别素材布局模式，在【技术】段明确标注格式：\n")
+	sb.WriteString("   *** 关键：帧间间隙必须留足8-16px纯白色(#FFFFFF)空白区域，间隙内不得有任何像素，确保投影法能可靠检测到间隙 ***\n")
 	switch in.AssetType {
 	case "sprite":
 		sb.WriteString("   - 单个精灵(默认)：独立PNG，纯白色背景(#FFFFFF)，描述为单个角色立绘/道具图标\n")
-		sb.WriteString("   - 精灵表(spritesheet)：角色/道具按行列等距网格排列，纯白色背景(#FFFFFF)，帧间固定间距(2-4px)，标注行列数，便于脚本一键拆分\n")
+		sb.WriteString("   - 精灵表(spritesheet)：角色/道具按行列等距网格排列，纯白色背景(#FFFFFF)，帧间留8-16px纯白间隙（无像素残留），标注行列数\n")
 	case "background":
 		sb.WriteString("   - 独立场景(默认)：单张完整背景图，层次分明\n")
-		sb.WriteString("   - 场景瓦片集(tileset)：地形/建筑元件按规则网格排列，纯白色背景(#FFFFFF)，元件间固定间距，标注行列数与瓦片尺寸，确保无缝拼接\n")
+		sb.WriteString("   - 场景瓦片集(tileset)：地形/建筑元件按规则网格排列，纯白色背景(#FFFFFF)，元件间留8-16px纯白间隙，标注行列数与瓦片尺寸\n")
 	case "ui":
 		sb.WriteString("   - 独立UI元素(默认)：单个按钮/面板/图标，纯白色背景(#FFFFFF)，独立PNG\n")
-		sb.WriteString("   - UI瓦片集(tileset)：UI元件按规则网格排列，纯白色背景(#FFFFFF)，元件间固定间距，标注行列数，支持九宫格缩放，便于脚本一键拆分\n")
+		sb.WriteString("   - UI瓦片集(tileset)：UI元件按规则网格排列，纯白色背景(#FFFFFF)，元件间留8-16px纯白间隙，标注行列数，支持九宫格缩放\n")
 	case "animation":
 		sb.WriteString("   - 帧序列(默认)：连续动画帧，独立帧文件或帧条带，纯白色背景(#FFFFFF)\n")
-		sb.WriteString("   - 动画精灵表(spritesheet)：动画帧按行列等距网格排列，纯白色背景(#FFFFFF)，帧间固定间距，标注行列数与方向数，便于脚本一键拆分\n")
+		sb.WriteString("   - 动画精灵表(spritesheet)：动画帧按行列等距网格排列，纯白色背景(#FFFFFF)，帧间留8-16px纯白间隙（无像素残留），标注行列数与方向数\n")
 	}
 	sb.WriteString("\n\n")
 
@@ -360,22 +361,22 @@ func buildTechNotes(assetType string, isSheet bool) string {
 	switch assetType {
 	case "sprite":
 		if isSheet {
-			return "输出格式: spritesheet；行列间隔完全相等、可脚本一键拆分对齐；纯白色背景(#FFFFFF，无渐变无噪点)；帧间固定间距(2-4px)；标注行列数"
+			return "输出格式: spritesheet；帧间留8-16px纯白间隙（间隙内无任何像素），行/列间隙完全相等；纯白色背景(#FFFFFF，无渐变无噪点)；标注行列数"
 		}
 		return "输出格式: 独立PNG；纯白色背景(#FFFFFF)；尺寸: 按角色比例适配"
 	case "background":
 		if isSheet {
-			return "输出格式: 场景瓦片集(tileset)；规则网格排列；纯白色背景(#FFFFFF)；瓦片间固定间距；标注行列数与瓦片尺寸；确保无缝拼接"
+			return "输出格式: 场景瓦片集(tileset)；规则网格排列；纯白色背景(#FFFFFF)；元件间留8-16px纯白间隙；标注行列数与瓦片尺寸；确保无缝拼接"
 		}
 		return "输出格式: 独立PNG；分辨率: 1920x1080；层次分明的前中后景"
 	case "ui":
 		if isSheet {
-			return "输出格式: UI瓦片集(tileset)；规则网格排列；纯白色背景(#FFFFFF)；元件间固定间距；标注行列数；支持九宫格缩放；可脚本一键拆分"
+			return "输出格式: UI瓦片集(tileset)；规则网格排列；纯白色背景(#FFFFFF)；元件间留8-16px纯白间隙；标注行列数；支持九宫格缩放；可脚本一键拆分"
 		}
 		return "输出格式: 独立PNG素材；纯白色背景(#FFFFFF)；分辨率: 按元素适配；支持九宫格缩放"
 	case "animation":
 		if isSheet {
-			return "输出格式: 动画精灵表(spritesheet)；行列间隔相等；纯白色背景(#FFFFFF，无渐变无噪点)；帧间固定间距；标注行列数与方向数；可脚本一键拆分"
+			return "输出格式: 动画精灵表(spritesheet)；帧间留8-16px纯白间隙（间隙内无任何像素），行/列间隙相等；纯白色背景(#FFFFFF，无渐变无噪点)；标注行列数与方向数"
 		}
 		return "输出格式: 帧序列或帧条带；独立帧文件；纯白色背景(#FFFFFF)；建议4方向x4帧"
 	default:

backend/pkg/gifmaker/gifmaker.go

@@ -0,0 +1,128 @@
+// Package gifmaker encodes sprite animation frames into a GIF preview.
+//
+// Features:
+//   - Unified canvas: all frames normalized to the same dimensions
+//   - Transparent background: palette index 0 = fully transparent
+//   - DisposalBackground: each frame clears the previous one, no ghosting
+//
+// Pipeline integration:
+//
+//	frames, _ := splitsprite.Process(img, splitsprite.DefaultOptions())
+//	gifmaker.Save("preview.gif", frames, nil)
+package gifmaker
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"image/gif"
+	"io"
+	"os"
+)
+
+// Options configures GIF generation.
+type Options struct {
+	// Delay is the frame delay in 1/100s (default 10).
+	Delay int
+	// MaxColors is the maximum palette size (default 256).
+	MaxColors int
+}
+
+// DefaultOptions returns sensible defaults.
+func DefaultOptions() *Options {
+	return &Options{
+		Delay:     10,
+		MaxColors: 256,
+	}
+}
+
+// Save is a convenience wrapper that writes frames to a GIF file.
+func Save(path string, frames []image.Image, opts *Options) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return fmt.Errorf("create gif file: %w", err)
+	}
+	defer f.Close()
+	return Encode(f, frames, opts)
+}
+
+// Encode writes an animated GIF to w. All frames are normalized to a unified
+// canvas (max width/height across frames), the palette starts with a
+// transparent color, and DisposalBackground prevents inter-frame ghosting.
+func Encode(w io.Writer, frames []image.Image, opts *Options) error {
+	if len(frames) == 0 {
+		return fmt.Errorf("no frames to encode")
+	}
+	if opts == nil {
+		opts = DefaultOptions()
+	}
+	delay := opts.Delay
+	if delay <= 0 {
+		delay = 10
+	}
+	maxColors := opts.MaxColors
+	if maxColors <= 0 || maxColors > 256 {
+		maxColors = 256
+	}
+
+	// Unified canvas
+	maxW, maxH := 0, 0
+	for _, f := range frames {
+		b := f.Bounds()
+		if b.Dx() > maxW {
+			maxW = b.Dx()
+		}
+		if b.Dy() > maxH {
+			maxH = b.Dy()
+		}
+	}
+
+	// Palette with transparent at index 0
+	pal := color.Palette{color.RGBA{0, 0, 0, 0}}
+	seen := make(map[color.RGBA]bool)
+	for _, fr := range frames {
+		b := fr.Bounds()
+		for y := b.Min.Y; y < b.Max.Y; y += 3 {
+			for x := b.Min.X; x < b.Max.X; x += 3 {
+				r, g, bl, a := fr.At(x, y).RGBA()
+				c := color.RGBA{uint8(r >> 8), uint8(g >> 8), uint8(bl >> 8), uint8(a >> 8)}
+				if !seen[c] && len(pal) < maxColors-1 {
+					seen[c] = true
+					pal = append(pal, c)
+				}
+			}
+		}
+	}
+
+	anim := &gif.GIF{
+		Config: image.Config{Width: maxW, Height: maxH},
+	}
+
+	for _, frame := range frames {
+		pl := image.NewPaletted(image.Rect(0, 0, maxW, maxH), pal)
+		// Manually map pixels: transparent → index 0, colored → nearest palette
+		b := frame.Bounds()
+		for y := 0; y < maxH; y++ {
+			for x := 0; x < maxW; x++ {
+				sx := x + b.Min.X
+				sy := y + b.Min.Y
+				if sx < b.Max.X && sy < b.Max.Y {
+					r, g, bl, a := frame.At(sx, sy).RGBA()
+					if a > 0 {
+						c := color.RGBA{uint8(r >> 8), uint8(g >> 8), uint8(bl >> 8), uint8(a >> 8)}
+						pl.Set(x, y, c)
+					}
+					// else: stays at index 0 (transparent)
+				}
+			}
+		}
+
+		anim.Image = append(anim.Image, pl)
+		anim.Delay = append(anim.Delay, delay)
+		anim.Disposal = append(anim.Disposal, gif.DisposalBackground)
+	}
+
+	anim.LoopCount = 0
+	anim.BackgroundIndex = 0
+	return gif.EncodeAll(w, anim)
+}

backend/pkg/splitsprite/splitsprite.go

@@ -58,8 +58,9 @@ func DefaultOptions() *Options {
 		WhiteThreshold: 40,
 		GapThreshold:   0.03,
 		MinGapWidth:    2,
-		MinFillRatio:   0.3,
+		MinFillRatio:   0.14,
 		Trim:           true,
+		CenterAlign:    true,
 	}
 }
 
@@ -70,8 +71,9 @@ func DefaultGreenOptions() *Options {
 		GreenTolerance: 0.2,
 		GapThreshold:   0.03,
 		MinGapWidth:    2,
-		MinFillRatio:   0.3,
+		MinFillRatio:   0.14,
 		Trim:           true,
+		CenterAlign:    true,
 	}
 }
 
@@ -133,14 +135,15 @@ func CenterFrames(frames []image.Image) []image.Image {
 	return alignCenter(frames)
 }
 
-// alignCenter finds the content bounding box per frame, computes the max
-// dimensions, then pads each frame so content is centered uniformly.
+// alignCenter aligns all frames to a uniform canvas with a fixed reference point.
+// Uses bottom-center alignment so characters share a common ground plane across frames,
+// preventing drift/jitter in animation playback.
 func alignCenter(frames []image.Image) []image.Image {
 	type contentBox struct {
 		minX, minY, maxX, maxY int
 	}
 	boxes := make([]contentBox, len(frames))
-	maxW, maxH := 0, 0
+	maxCW, maxCH := 0, 0
 
 	for i, f := range frames {
 		b := f.Bounds()
@@ -172,29 +175,32 @@ func alignCenter(frames []image.Image) []image.Image {
 		} else {
 			boxes[i] = contentBox{minX, minY, maxX, maxY}
 		}
-		w := boxes[i].maxX - boxes[i].minX + 1
-		h := boxes[i].maxY - boxes[i].minY + 1
-		if w > maxW {
-			maxW = w
+		cw := boxes[i].maxX - boxes[i].minX + 1
+		ch := boxes[i].maxY - boxes[i].minY + 1
+		if cw > maxCW {
+			maxCW = cw
 		}
-		if h > maxH {
-			maxH = h
+		if ch > maxCH {
+			maxCH = ch
 		}
 	}
 
-	// Pad by 10% to avoid edge cropping
-	maxW = maxW * 11 / 10
-	maxH = maxH * 11 / 10
+	// Uniform canvas with 10% padding
+	canvasW := maxCW * 11 / 10
+	canvasH := maxCH * 11 / 10
+	// Fixed X center reference: anchor all frames to the same horizontal center
+	fixedCenterX := canvasW / 2
 
 	out := make([]image.Image, len(frames))
 	for i, f := range frames {
 		cb := boxes[i]
 		cw := cb.maxX - cb.minX + 1
 		ch := cb.maxY - cb.minY + 1
-		ox := (maxW - cw) / 2
-		oy := (maxH - ch) / 2
+		// All frames share the same center-X and bottom-Y anchor
+		ox := fixedCenterX - cw/2 // consistent horizontal center
+		oy := canvasH - ch        // bottom-align: feet planted at same Y
 
-		canvas := image.NewRGBA(image.Rect(0, 0, maxW, maxH))
+		canvas := image.NewRGBA(image.Rect(0, 0, canvasW, canvasH))
 		draw.Draw(canvas,
 			image.Rect(ox, oy, ox+cw, oy+ch),
 			f,
@@ -229,7 +235,7 @@ type tile struct {
 	x, y, w, h int
 }
 
-// removeWhiteBg removes pixels close to pure white (R,G,B all above threshold).
+// removeWhiteBg removes pixels close to pure white (R,G,B all within threshold of 255).
 func removeWhiteBg(rgba *image.RGBA, threshold uint8) *image.RGBA {
 	if threshold == 0 {
 		threshold = 40
@@ -245,11 +251,14 @@ func removeWhiteBg(rgba *image.RGBA, threshold uint8) *image.RGBA {
 				continue
 			}
 			r8, g8, b8 := uint8(r>>8), uint8(g>>8), uint8(bl>>8)
-			// Pixel is "white" when all channels are near 255
-			if int(255-r8) < int(threshold) && int(255-g8) < int(threshold) && int(255-b8) < int(threshold) {
-				// Calculate alpha: closer to white = more transparent
+			// Distance from pure white
 			dist := max(int(255-r8), max(int(255-g8), int(255-b8)))
-				alpha := float64(dist) / float64(threshold)
+			if dist < int(threshold)/2 {
+				// Very close to white — fully transparent
+				dst.SetRGBA(x, y, color.RGBA{R: r8, G: g8, B: b8, A: 0})
+			} else if dist < int(threshold) {
+				// Semi-white — fade alpha
+				alpha := float64(dist-int(threshold)/2) / float64(int(threshold)/2)
 				dst.SetRGBA(x, y, color.RGBA{R: r8, G: g8, B: b8, A: uint8(alpha * 255)})
 			}
 		}
@@ -378,6 +387,90 @@ func tileFillRatio(rgba *image.RGBA, x0, y0, w, h int) float64 {
 }
 
 func findCuts(ratios []float64, threshold float64, minGap int) []int {
+	n := len(ratios)
+	if n == 0 {
+		return nil
+	}
+
+	// Smooth the ratio curve with a moving average (kernel size = minGap)
+	smoothed := make([]float64, n)
+	kernel := max(minGap, 3)
+	for i := 0; i < n; i++ {
+		sum := 0.0
+		count := 0
+		for j := max(0, i-kernel/2); j < min(n, i+kernel/2+1); j++ {
+			sum += ratios[j]
+			count++
+		}
+		if count > 0 {
+			smoothed[i] = sum / float64(count)
+		}
+	}
+
+	// Compute mean to use as reference
+	mean := 0.0
+	for _, r := range smoothed {
+		mean += r
+	}
+	mean /= float64(n)
+
+	// Find peaks: contiguous regions where smoothed ratio > mean*1.2
+	type segment struct{ start, end int }
+	var peaks []segment
+	i := 0
+	for i < n {
+		if smoothed[i] > mean*1.2 {
+			start := i
+			for i < n && smoothed[i] > mean*0.8 {
+				i++
+			}
+			peaks = append(peaks, segment{start, i})
+		} else {
+			i++
+		}
+	}
+
+	if len(peaks) < 2 {
+		// Fallback: use threshold-based gap detection
+		return findCutsByGap(ratios, threshold, minGap)
+	}
+
+	// Find valleys between adjacent peaks (minimum smoothed ratio between them)
+	cuts := []int{0}
+	for p := 0; p < len(peaks)-1; p++ {
+		valleyStart := peaks[p].end
+		valleyEnd := peaks[p+1].start
+		if valleyStart >= valleyEnd {
+			// Peaks adjacent — cut at midpoint
+			cuts = append(cuts, (peaks[p].end+peaks[p+1].start)/2)
+			continue
+		}
+		// Find minimum in the valley region
+		minIdx := valleyStart
+		minVal := smoothed[valleyStart]
+		for j := valleyStart + 1; j < valleyEnd; j++ {
+			if smoothed[j] < minVal {
+				minVal = smoothed[j]
+				minIdx = j
+			}
+		}
+		cuts = append(cuts, minIdx)
+	}
+	cuts = append(cuts, n)
+	sort.Ints(cuts)
+
+	// Deduplicate
+	dedup := cuts[:1]
+	for j := 1; j < len(cuts); j++ {
+		if cuts[j] != dedup[len(dedup)-1] {
+			dedup = append(dedup, cuts[j])
+		}
+	}
+	return dedup
+}
+
+// findCutsByGap is the original threshold-based fallback.
+func findCutsByGap(ratios []float64, threshold float64, minGap int) []int {
 	n := len(ratios)
 	isGap := make([]bool, n)
 	for i, r := range ratios {

backend/tools/test_prompt_to_gif.go

@@ -7,14 +7,12 @@ import (
 	"context"
 	"fmt"
 	"image"
-	"image/color"
-	"image/draw"
-	"image/gif"
 	"image/png"
 	"os"
 
 	"gen2d/internal/config"
 	"gen2d/internal/service"
+	"gen2d/pkg/gifmaker"
 	"gen2d/pkg/splitsprite"
 )
 
@@ -28,10 +26,10 @@ func main() {
 	// 1. PromptAgent 优化提示词
 	fmt.Println("=== Step 1: Optimize prompt via PromptAgent ===")
 	agentIn := service.PromptAgentInput{
-		Tags:      []string{"像素", "战士", "持剑", "精灵表"},
+		Tags:      []string{"像素", "横版动作", "大剑战士", "精灵表", "4x4网格"},
 		AssetType: "sprite",
-		Prompt:    "生成一个像素风持剑战士的4方向行走精灵表",
-		UserNote:  "需要4方向（上下左右），每方向4帧行走动画",
+		Prompt:    "生成一个2D横版动作游戏角色的连续攻击连招精灵表，侧视角，4行4列网格排列",
+		UserNote:  "角色为持大剑的战士，连招包含4段攻击：横斩→上挑→跳劈→终结重击。每段攻击4帧关键帧，共16帧，按4行×4列网格排列。帧间留8-16px纯白间隙(#FFFFFF)。要求动作流畅有力量感，大剑挥舞轨迹清晰",
 	}
 	out, err := service.RunPromptAgent(ctx, agentIn)
 	if err != nil {
@@ -42,7 +40,7 @@ func main() {
 	// 2. 调用文生图 API
 	fmt.Println("=== Step 2: Generate sprite sheet via image API ===")
 	params := service.AssetParams{
-		Resolution: 1024,
+		Resolution: 1536,
 		Format:     "spritesheet",
 	}
 	images, err := service.GenerateImages(ctx, out.Prompt, params)
@@ -63,17 +61,13 @@ func main() {
 	}
 	fmt.Printf("Saved sprite sheet → %s (%d bytes)\n", sheetPath, len(images[0].Data))
 
-	// 3. splitsprite 拆分精灵表
-	fmt.Println("\n=== Step 3: Split sprite sheet ===")
+	// 3. splitsprite: 洗白底 → 波谷投影拆分 → 有效像素≥40% → 裁切像素边界 → 统一最大分辨率居中
+	fmt.Println("\n=== Step 3: Wash white bg → valley projection split → trim → center align ===")
 	sheetImg, err := decodePNG(images[0].Data)
 	if err != nil {
 		fatalf("decode sheet: %v", err)
 	}
-	opts := splitsprite.DefaultOptions()
-	opts.GridRows = 4
-	opts.GridCols = 4
-	opts.GridPadding = 2
-	opts.CenterAlign = true
+	opts := splitsprite.DefaultOptions() // WhiteBg=true, MinFillRatio=0.4, CenterAlign=true
 	frames, err := splitsprite.Process(sheetImg, opts)
 	if err != nil {
 		fatalf("split failed: %v", err)
@@ -92,7 +86,7 @@ func main() {
 	// 4. 生成 GIF 预览
 	fmt.Println("\n=== Step 4: Generate GIF preview ===")
 	gifPath := "test_output/preview.gif"
-	if err := genGIF(gifPath, frames, 12); err != nil {
+	if err := gifmaker.Save(gifPath, frames, nil); err != nil {
 		fatalf("generate GIF: %v", err)
 	}
 	fmt.Printf("GIF preview → %s (%d frames)\n", gifPath, len(frames))
@@ -104,63 +98,6 @@ func main() {
 	fmt.Println("  test_output/preview.gif       — animated GIF preview")
 }
 
-func genGIF(path string, frames []image.Image, delay int) error {
-	f, err := os.Create(path)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	pal := buildPalette(frames)
-	anim := &gif.GIF{}
-	for _, frame := range frames {
-		b := frame.Bounds()
-		paletted := image.NewPaletted(b, pal)
-		draw.Draw(paletted, b, frame, b.Min, draw.Src)
-		anim.Image = append(anim.Image, paletted)
-		anim.Delay = append(anim.Delay, delay)
-	}
-	anim.LoopCount = 0 // loop forever
-	return gif.EncodeAll(f, anim)
-}
-
-func buildPalette(frames []image.Image) color.Palette {
-	hist := make(map[color.RGBA]int)
-	sampleStep := max(1, len(frames)/8)
-	for i := 0; i < len(frames); i += sampleStep {
-		b := frames[i].Bounds()
-		step := max(1, (b.Dx()*b.Dy())/4096)
-		n := 0
-		for y := b.Min.Y; y < b.Max.Y; y++ {
-			for x := b.Min.X; x < b.Max.X; x++ {
-				if n%step != 0 {
-					n++
-					continue
-				}
-				n++
-				r, g, bl, a := frames[i].At(x, y).RGBA()
-				if a > 0 {
-					c := color.RGBA{R: uint8(r >> 8), G: uint8(g >> 8), B: uint8(bl >> 8), A: uint8(a >> 8)}
-					hist[c]++
-				}
-			}
-		}
-	}
-	pal := make(color.Palette, 0, 256)
-	for c := range hist {
-		pal = append(pal, c)
-		if len(pal) >= 240 {
-			break
-		}
-	}
-	pal = append(pal,
-		color.RGBA{0, 0, 0, 0},
-		color.RGBA{0, 0, 0, 255},
-		color.RGBA{255, 255, 255, 255},
-	)
-	return pal
-}
-
 func decodePNG(data []byte) (image.Image, error) {
 	img, _, err := image.Decode(bytes.NewReader(data))
 	if err != nil {