feat(后端结构): 完善多后端解耦，清理遗留代码

ofdgo_paint_model.go

@@ -0,0 +1,87 @@
+// 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 "image/color"
+
+// ColorStop 保存预乘RGBA颜色节点及渐变区间位置
+type ColorStop struct {
+	Offset float64
+	Color  color.RGBA
+}
+
+// PaintKind 区分无画刷、纯色、轴向渐变、径向渐变和图案
+type PaintKind uint8
+
+const (
+	PaintNone PaintKind = iota
+	PaintSolid
+	PaintLinear
+	PaintRadial
+	PaintPattern
+)
+
+// Paint 保存后端无关的颜色、渐变和图案，不修改源节点
+type Paint struct {
+	Kind     PaintKind
+	Color    color.RGBA
+	Gradient *Shading
+	Pattern  *PatternPaint
+}
+
+// Shading 保存OFD对象局部坐标中的渐变，单位为毫米，纵轴向下
+// Extend、MapType和MapUnit保留标准的延伸及重复语义
+type Shading struct {
+	Start, End                   Point
+	StartRadius, EndRadius       float64
+	Stops                        []ColorStop
+	Extend, MapType              string
+	MapUnit, Eccentricity, Angle float64
+}
+
+// ResolvePaint 解析颜色、透明度、渐变分段和图案，不依赖绘图库
+// 入参: fill 填充或转换后的描边节点
+// 返回: Paint 只读画刷
+func (r *Renderer) ResolvePaint(fill *FillColor) Paint {
+	if fill == nil {
+		return Paint{}
+	}
+	if fill.Pattern != nil {
+		return Paint{Kind: PaintPattern, Pattern: parsePatternPaint(fill)}
+	}
+	base := r.parseFillColor(fill)
+	if base == nil {
+		return Paint{}
+	}
+	paint := Paint{Kind: PaintSolid, Color: colorToRGBA(base)}
+	if node := fill.AxialShd; node != nil {
+		start, end := parseFloats(node.StartPoint), parseFloats(node.EndPoint)
+		stops := r.GradientStops(node.Segment, fill.Alpha)
+		if len(start) >= 2 && len(end) >= 2 && len(stops) != 0 && (!geometryEqual(start[0], end[0]) || !geometryEqual(start[1], end[1])) {
+			paint.Kind = PaintLinear
+			paint.Gradient = &Shading{Start: Point{X: start[0], Y: start[1]}, End: Point{X: end[0], Y: end[1]}, Stops: stops, Extend: node.Extend, MapType: node.MapType, MapUnit: node.MapUnit}
+			return paint
+		}
+	}
+	if node := fill.RadialShd; node != nil && node.EndRadius > 0 {
+		start, end := parseFloats(node.StartPoint), parseFloats(node.EndPoint)
+		stops := r.GradientStops(node.Segment, fill.Alpha)
+		if len(start) >= 2 && len(end) >= 2 && len(stops) != 0 {
+			paint.Kind = PaintRadial
+			paint.Gradient = &Shading{Start: Point{X: start[0], Y: start[1]}, End: Point{X: end[0], Y: end[1]}, StartRadius: node.StartRadius, EndRadius: node.EndRadius, Stops: stops, Extend: node.Extend, MapType: node.MapType, MapUnit: node.MapUnit, Eccentricity: node.Eccentricity, Angle: node.Angle}
+		}
+	}
+	return paint
+}