feat(后端架构): 接入GoGPU渲染，支持后端切换

ofdgo_raster.go

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+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ofdgo
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"math"
+)
+
+// RasterPage 已解析的光栅绘制页面，单位为毫米，页面坐标原点在左上角
+// DPI决定像素尺寸和编译时的字形、描边精度，修改DPI后应重新编译
+// 页面及其引用资源在渲染期间只读，不用于重建或保存OFD
+type RasterPage struct {
+	Width, Height float64
+	DPI           float64
+	Commands      []RasterCommand
+}
+
+// RasterMatrix 按a、b、c、d、e、f排列的仿射矩阵，零值不是单位矩阵
+type RasterMatrix [6]float64
+
+// RasterPoint 路径或渐变坐标
+type RasterPoint struct{ X, Y float64 }
+
+// RasterVerb 路径指令
+type RasterVerb uint8
+
+const (
+	RasterMove RasterVerb = iota
+	RasterLine
+	RasterQuad
+	RasterCubic
+	RasterClose
+)
+
+// RasterSegment 路径片段，RasterMove和RasterLine使用End，RasterQuad使用Control1和End
+type RasterSegment struct {
+	Verb               RasterVerb
+	Control1, Control2 RasterPoint
+	End                RasterPoint
+}
+
+// RasterCommand 填充路径或绘制图像，Image非空时为图像指令
+// Transform将局部坐标映射到页面，图像局部坐标与image.Image的像素坐标一致
+// 字形和描边由页面编译器生成轮廓，裁剪与底纹在编译时解析
+type RasterCommand struct {
+	Path      []RasterSegment
+	Paint     RasterPaint
+	EvenOdd   bool
+	Transform RasterMatrix
+	Image     image.Image
+}
+
+// RasterPaint 预乘RGBA纯色或渐变，Gradient非空时忽略Color
+type RasterPaint struct {
+	Color    color.RGBA
+	Gradient *RasterGradient
+}
+
+// RasterGradientKind 渐变类型
+type RasterGradientKind uint8
+
+const (
+	RasterLinear RasterGradientKind = iota
+	RasterRadial
+)
+
+// RasterStop 按Offset升序排列的预乘RGBA颜色节点
+type RasterStop struct {
+	Offset float64
+	Color  color.RGBA
+}
+
+// RasterGradient 局部坐标下的线性或双圆径向渐变，区间外延续边界颜色
+type RasterGradient struct {
+	Kind       RasterGradientKind
+	Start, End RasterPoint
+	R0, R1     float64
+	Stops      []RasterStop
+}
+
+// PixelSize 检查页面尺寸并计算目标像素大小
+// 返回: int 宽度, int 高度, error 无效尺寸
+func (p *RasterPage) PixelSize() (int, int, error) {
+	if p == nil || !rasterPositive(p.Width) || !rasterPositive(p.Height) || !rasterPositive(p.DPI) {
+		return 0, 0, fmt.Errorf("invalid raster page size or DPI")
+	}
+	scale := p.DPI / 25.4
+	w, h := math.Floor(p.Width*scale+0.5), math.Floor(p.Height*scale+0.5)
+	if !rasterPositive(w) || !rasterPositive(h) || w*h > math.MaxInt32/4 {
+		return 0, 0, fmt.Errorf("invalid raster pixel dimensions: %g x %g", w, h)
+	}
+	return int(w), int(h), nil
+}
+
+// rasterPositive 判断正有限数
+// 入参: v 待检查数值
+// 返回: bool 是否为正有限数
+func rasterPositive(v float64) bool { return v > 0 && !math.IsInf(v, 0) && !math.IsNaN(v) }
+
+// Apply 将局部点映射到目标坐标
+// 入参: p 局部点
+// 返回: RasterPoint 目标点
+func (m RasterMatrix) Apply(p RasterPoint) RasterPoint {
+	return RasterPoint{m[0]*p.X + m[2]*p.Y + m[4], m[1]*p.X + m[3]*p.Y + m[5]}
+}
+
+// Inverse 求逆矩阵，退化或行列式非有限时返回错误
+// 返回: RasterMatrix 逆矩阵, error 无效矩阵
+func (m RasterMatrix) Inverse() (RasterMatrix, error) {
+	det := m[0]*m[3] - m[1]*m[2]
+	if det == 0 || math.IsNaN(det) || math.IsInf(det, 0) {
+		return RasterMatrix{}, fmt.Errorf("invalid raster transform")
+	}
+	return RasterMatrix{m[3] / det, -m[1] / det, -m[2] / det, m[0] / det,
+		(m[2]*m[5] - m[3]*m[4]) / det, (m[1]*m[4] - m[0]*m[5]) / det}, nil
+}
+
+// At 采样局部坐标下的渐变，使用预乘颜色插值
+// 入参: x 横坐标, y 纵坐标
+// 返回: color.RGBA 采样颜色
+func (g *RasterGradient) At(x, y float64) color.RGBA {
+	dx, dy := g.End.X-g.Start.X, g.End.Y-g.Start.Y
+	px, py := x-g.Start.X, y-g.Start.Y
+	t := 0.0
+	if g.Kind == RasterRadial {
+		dr := g.R1 - g.R0
+		a, b, c := dx*dx+dy*dy-dr*dr, -2*(px*dx+py*dy+g.R0*dr), px*px+py*py-g.R0*g.R0
+		t = rasterRadialPosition(a, b, c, g.R0, dr)
+	} else if length := dx*dx + dy*dy; length > 0 {
+		t = (px*dx + py*dy) / length
+	}
+	return g.colorAt(t)
+}
+
+// rasterRadialPosition 求双圆渐变中半径非负的有效参数
+// 入参: a 二次项系数, b 一次项系数, c 常数项, radius 起始半径, delta 半径增量
+// 返回: float64 渐变位置，范围为0至1
+func rasterRadialPosition(a, b, c, radius, delta float64) float64 {
+	x, y := math.NaN(), math.NaN()
+	if a == 0 {
+		if b != 0 {
+			x = -c / b
+		}
+	} else if d := b*b - 4*a*c; d >= 0 {
+		q := -0.5 * (b + math.Copysign(math.Sqrt(d), b))
+		if q == 0 {
+			x = -b / (2 * a)
+		} else {
+			x, y = q/a, c/q
+			if x > y {
+				x, y = y, x
+			}
+		}
+	}
+	for _, t := range []float64{y, x} {
+		if t >= 0 && t <= 1 && radius+delta*t >= 0 {
+			return t
+		}
+	}
+	for _, t := range []float64{x, y} {
+		if t > 0 && radius+delta*t >= 0 {
+			return 1
+		}
+	}
+	return 0
+}
+
+// colorAt 插值有序颜色节点
+// 入参: t 渐变位置
+// 返回: color.RGBA 预乘颜色
+func (g *RasterGradient) colorAt(t float64) color.RGBA {
+	if len(g.Stops) == 0 {
+		return color.RGBA{}
+	}
+	if t <= g.Stops[0].Offset {
+		return g.Stops[0].Color
+	}
+	for i := 1; i < len(g.Stops); i++ {
+		before, after := g.Stops[i-1], g.Stops[i]
+		if t < after.Offset {
+			u := uint32((t-before.Offset)/(after.Offset-before.Offset)*65535 + 0.5)
+			blend := func(a, b uint8) uint8 { return uint8(((65535-u)*uint32(a)*257 + u*uint32(b)*257) >> 24) }
+			return color.RGBA{blend(before.Color.R, after.Color.R), blend(before.Color.G, after.Color.G), blend(before.Color.B, after.Color.B), blend(before.Color.A, after.Color.A)}
+		}
+	}
+	return g.Stops[len(g.Stops)-1].Color
+}