feat(图像性能): 保留图像精度并加速缩放

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/tdewolff/canvas v0.0.0-20260923214215-09804640d00c
 	github.com/tdewolff/font v0.0.0-20260913163313-54f98bb59ee6
 	github.com/xiaoqidun/jbig2 v1.1.1
-	github.com/xiaoqidun/pdfgo v0.0.0-20260927114248-f2deafc71b89
+	github.com/xiaoqidun/pdfgo v0.0.0-20260927123406-320d8b5546b5
 	golang.org/x/crypto v0.57.0
 	golang.org/x/image v0.46.0
 	golang.org/x/text v0.42.0

go.sum

@@ -62,8 +62,8 @@ github.com/tdewolff/test v1.0.12 h1:7F21DqIajswxuche0geHdrUZRCWE4oko4b7bcmkkrxk=
 github.com/tdewolff/test v1.0.12/go.mod h1:XPuWBzvdUzhCuxWO1ojpXsyzsA5bFoS3tO/Q3kFuTG8=
 github.com/xiaoqidun/jbig2 v1.1.1 h1:SjliS9ZO0e9HX5oYUfBuXrfFsXhWricrSz+XY4zORDI=
 github.com/xiaoqidun/jbig2 v1.1.1/go.mod h1:8QonVWtENmh2kc6l+leqeGl7psb79DWlHDkCpdChjfQ=
-github.com/xiaoqidun/pdfgo v0.0.0-20260927114248-f2deafc71b89 h1:pdnJkITNBORnYyoqU0u9MDHpjwnALvkiBS8cdJFRTRg=
+github.com/xiaoqidun/pdfgo v0.0.0-20260927123406-320d8b5546b5 h1:FyW2HSyxcrf33xo3F1eKVZmlizgpxML2H+qn63yXcDI=
-github.com/xiaoqidun/pdfgo v0.0.0-20260927114248-f2deafc71b89/go.mod h1:4Pf0JO0BEf1uzRY+uZjlMjN/OPn3PYa0YMi6cqPPTLQ=
+github.com/xiaoqidun/pdfgo v0.0.0-20260927123406-320d8b5546b5/go.mod h1:4Pf0JO0BEf1uzRY+uZjlMjN/OPn3PYa0YMi6cqPPTLQ=
 github.com/xyproto/randomstring v1.0.5 h1:YtlWPoRdgMu3NZtP45drfy1GKoojuR7hmRcnhZqKjWU=
 github.com/xyproto/randomstring v1.0.5/go.mod h1:rgmS5DeNXLivK7YprL0pY+lTuhNQW3iGxZ18UQApw/E=
 github.com/yuin/goldmark v1.8.5 h1:r6N5afV5qj/5S4UTch8agZHJ8UxNCMwX7WjkkJam2NA=

ofdgo_image.go

@@ -426,6 +426,9 @@ func imageWithTransparentEdge(img image.Image) (image.Image, int) {
 	if opaque, ok := source.(interface{ Opaque() bool }); ok && opaque.Opaque() {
 		return img, 0
 	}
+	if model := source.ColorModel(); model == color.NRGBA64Model || model == color.RGBA64Model || model == color.Alpha16Model || model == color.Gray16Model {
+		return imageWithTransparentEdge64(img, source)
+	}
 	hasZero, hasVisible := false, false
 	src, ok := source.(*image.NRGBA)
 	if ok {
@@ -510,3 +513,81 @@ func (s *transparentEdgeImage) RGBA64At(x, y int) color.RGBA64 {
 	r, g, b, a := s.NRGBAAt(x, y).RGBA()
 	return color.RGBA64{R: uint16(r), G: uint16(g), B: uint16(b), A: uint16(a)}
 }
+
+// imageWithTransparentEdge64 保留十六位颜色和透明度，不经八位图像中转
+// 入参: original 原始图像, source 已解码的像素源
+// 返回: image.Image 边缘处理结果, int 补齐像素数
+func imageWithTransparentEdge64(original, source image.Image) (image.Image, int) {
+	bounds := source.Bounds()
+	hasZero, hasVisible := false, false
+	for y := bounds.Min.Y; y < bounds.Max.Y && !(hasZero && hasVisible); y++ {
+		for x := bounds.Min.X; x < bounds.Max.X; x++ {
+			_, _, _, a := source.At(x, y).RGBA()
+			if a == 0 {
+				hasZero = true
+			} else {
+				hasVisible = true
+			}
+			if hasZero && hasVisible {
+				break
+			}
+		}
+	}
+	if !hasZero || !hasVisible {
+		return original, 0
+	}
+	return &transparentEdgeImage64{source: source, rect: image.Rect(0, 0, bounds.Dx()+2, bounds.Dy()+2)}, 1
+}
+
+// transparentEdgeImage64 按需补齐十六位像素边缘，保留原始只读图像
+type transparentEdgeImage64 struct {
+	source image.Image
+	rect   image.Rectangle
+}
+
+// Bounds 返回含采样边距的图像边界
+// 返回: image.Rectangle 图像边界
+func (s *transparentEdgeImage64) Bounds() image.Rectangle { return s.rect }
+
+// ColorModel 返回十六位非预乘颜色模型
+// 返回: color.Model 颜色模型
+func (s *transparentEdgeImage64) ColorModel() color.Model { return color.NRGBA64Model }
+
+// At 读取十六位原始颜色，透明邻域使用最小非零透明度保留边缘颜色
+// 入参: x 横向坐标, y 纵向坐标
+// 返回: color.Color 非预乘颜色
+func (s *transparentEdgeImage64) At(x, y int) color.Color {
+	if !image.Pt(x, y).In(s.rect) {
+		return color.NRGBA64{}
+	}
+	b := s.source.Bounds()
+	sx, sy := b.Min.X+min(max(x-1, 0), b.Dx()-1), b.Min.Y+min(max(y-1, 0), b.Dy()-1)
+	c := color.NRGBA64Model.Convert(s.source.At(sx, sy)).(color.NRGBA64)
+	if c.A == 0 {
+		var best color.NRGBA64
+		for ny := max(sy-1, b.Min.Y); ny < min(sy+2, b.Max.Y); ny++ {
+			for nx := max(sx-1, b.Min.X); nx < min(sx+2, b.Max.X); nx++ {
+				v := color.NRGBA64Model.Convert(s.source.At(nx, ny)).(color.NRGBA64)
+				if v.A > best.A {
+					best = v
+				}
+			}
+		}
+		if best.A != 0 {
+			best.A = 1
+			c = best
+		}
+	}
+	if x == 0 || y == 0 || x == s.rect.Max.X-1 || y == s.rect.Max.Y-1 {
+		c.A = 1
+	}
+	return c
+}
+
+// RGBA64At 返回保留原采样精度的预乘颜色
+// 入参: x 横向坐标, y 纵向坐标
+// 返回: color.RGBA64 预乘颜色
+func (s *transparentEdgeImage64) RGBA64At(x, y int) color.RGBA64 {
+	r, g, b, a := s.At(x, y).RGBA()
+	return color.RGBA64{R: uint16(r), G: uint16(g), B: uint16(b), A: uint16(a)}
+}

ofdgo_raster_image.go

@@ -25,7 +25,41 @@ import (
 // drawRasterImage 按页面变换对图像执行高质量采样
 // 入参: dst 目标图像, src 源图像, m 像素坐标变换
 func drawRasterImage(dst draw.Image, src image.Image, m RasterMatrix) {
-	draw.CatmullRom.Transform(dst, f64.Aff3{m[0], m[2], m[4], m[1], m[3], m[5]}, src, src.Bounds(), draw.Over, nil)
+	drawRasterImagePixels(dst, src, m, draw.Over)
+}
+
+// drawRasterImagePixels 对整像素边界的轴向缩小使用可分离采样，其余变换保留通用路径
+// 入参: dst 目标图像, src 源图像, m 像素变换, op 合成操作
+func drawRasterImagePixels(dst draw.Image, src image.Image, m RasterMatrix, op draw.Op) {
+	b := src.Bounds()
+	if dr, ok := rasterScaleBounds(b, m); ok {
+		if dr.Intersect(dst.Bounds()).Empty() {
+			return
+		}
+		draw.CatmullRom.Scale(dst, dr, src, b, op, nil)
+		return
+	}
+	draw.CatmullRom.Transform(dst, f64.Aff3{m[0], m[2], m[4], m[1], m[3], m[5]}, src, b, op, nil)
+}
+
+// rasterScaleBounds 检查变换是否可无几何取整地使用缩放器，并避开其整数溢出范围
+// 入参: b 源边界, m 像素变换
+// 返回: image.Rectangle 缩放边界, bool 是否适用
+func rasterScaleBounds(b image.Rectangle, m RasterMatrix) (image.Rectangle, bool) {
+	if b.Empty() || m[1] != 0 || m[2] != 0 || m[0] <= 0 || m[0] > 1 || m[3] <= 0 || m[3] > 1 || m[0] == 1 && m[3] == 1 {
+		return image.Rectangle{}, false
+	}
+	x0, y0 := float64(m[0]*float64(b.Min.X))+m[4], float64(m[3]*float64(b.Min.Y))+m[5]
+	x1, y1 := float64(m[0]*float64(b.Max.X))+m[4], float64(m[3]*float64(b.Max.Y))+m[5]
+	for _, v := range [4]float64{x0, y0, x1, y1} {
+		if v != math.Floor(v) || v < math.MinInt32 || v > math.MaxInt32 {
+			return image.Rectangle{}, false
+		}
+	}
+	if x1 <= x0 || y1 <= y0 || b.Dx() > math.MaxInt32 || b.Dy() > math.MaxInt32 || (x1-x0)*float64(b.Dy()) > float64(min(math.MaxInt32, int(^uint(0)>>1)/32)) {
+		return image.Rectangle{}, false
+	}
+	return image.Rect(int(x0), int(y0), int(x1), int(y1)), true
 }
 
 // drawRasterImageCommand 使用当前后端生成裁剪蒙版，共用高质量图像采样
@@ -49,7 +83,7 @@ func drawRasterImageCommand(backend RasterBackend, page *RasterPage, dst draw.Im
 		return nil
 	}
 	layer := image.NewRGBA64(bounds)
-	draw.CatmullRom.Transform(layer, f64.Aff3{m[0], m[2], m[4], m[1], m[3], m[5]}, imagePixelSource(src), src.Bounds(), draw.Src, nil)
+	drawRasterImagePixels(layer, imagePixelSource(src), m, draw.Src)
 	draw.DrawMask(dst, bounds, layer, bounds.Min, mask, bounds.Min, draw.Over)
 	return nil
 }