feat(渲染编辑): 完善渲染编辑，优化版本压缩

ofdgo_mesh_sampler.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 (
+	"image/color"
+	"math"
+	"slices"
+)
+
+// MeshSampler 保存独立网格快照和空间索引，支持并发采样
+type MeshSampler struct {
+	mesh  MeshShading
+	nodes []meshSampleNode
+}
+
+// meshSampleNode 保存连续三角形组的包围盒及右子树位置
+type meshSampleNode struct {
+	minX, minY, maxX, maxY float64
+	right                  int
+}
+
+// NewSampler 创建网格快照，后续修改原网格不影响采样结果
+// 返回: *MeshSampler 只读采样器
+func (m *MeshShading) NewSampler() *MeshSampler {
+	s := &MeshSampler{}
+	if m != nil {
+		s.mesh = *m
+		s.mesh.Triangles = slices.Clone(m.Triangles)
+		if len(m.Triangles) > 8 {
+			s.build(0, len(m.Triangles))
+		}
+	}
+	return s
+}
+
+// At 采样快照中的预乘颜色，后绘制的三角形优先
+// 入参: x 横坐标, y 纵坐标
+// 返回: color.RGBA 预乘颜色
+func (s *MeshSampler) At(x, y float64) color.RGBA {
+	if len(s.nodes) == 0 || !finite(x) || !finite(y) {
+		return s.mesh.At(x, y)
+	}
+	if value, ok := s.sample(0, 0, len(s.mesh.Triangles), x, y); ok {
+		return value
+	}
+	return s.mesh.Background
+}
+
+// build 按绘制顺序构建包围盒层级，不重排原三角形
+// 入参: first 起始三角形, end 结束位置
+// 返回: int 节点位置
+func (s *MeshSampler) build(first, end int) int {
+	index := len(s.nodes)
+	s.nodes = append(s.nodes, meshSampleNode{})
+	if end-first <= 8 {
+		node := meshSampleNode{minX: math.Inf(1), minY: math.Inf(1), maxX: math.Inf(-1), maxY: math.Inf(-1)}
+		for _, triangle := range s.mesh.Triangles[first:end] {
+			a, b, c := triangle[0].Point, triangle[1].Point, triangle[2].Point
+			d := (b.Y-c.Y)*(a.X-c.X) + (c.X-b.X)*(a.Y-c.Y)
+			if !finite(d) {
+				node = meshSampleNode{minX: math.Inf(-1), minY: math.Inf(-1), maxX: math.Inf(1), maxY: math.Inf(1)}
+				break
+			}
+			for _, vertex := range triangle {
+				node.minX, node.minY = math.Min(node.minX, vertex.Point.X), math.Min(node.minY, vertex.Point.Y)
+				node.maxX, node.maxY = math.Max(node.maxX, vertex.Point.X), math.Max(node.maxY, vertex.Point.Y)
+			}
+		}
+		if finite(node.minX) && finite(node.minY) && finite(node.maxX) && finite(node.maxY) {
+			dx := 2e-12*(node.maxX-node.minX) + 1e-14*math.Max(math.Abs(node.minX), math.Abs(node.maxX))
+			dy := 2e-12*(node.maxY-node.minY) + 1e-14*math.Max(math.Abs(node.minY), math.Abs(node.maxY))
+			node.minX, node.maxX = math.Nextafter(node.minX-dx, math.Inf(-1)), math.Nextafter(node.maxX+dx, math.Inf(1))
+			node.minY, node.maxY = math.Nextafter(node.minY-dy, math.Inf(-1)), math.Nextafter(node.maxY+dy, math.Inf(1))
+		}
+		s.nodes[index] = node
+		return index
+	}
+	middle := first + (end-first)/2
+	left := s.build(first, middle)
+	right := s.build(middle, end)
+	a, b := s.nodes[left], s.nodes[right]
+	s.nodes[index] = meshSampleNode{minX: math.Min(a.minX, b.minX), minY: math.Min(a.minY, b.minY), maxX: math.Max(a.maxX, b.maxX), maxY: math.Max(a.maxY, b.maxY), right: right}
+	return index
+}
+
+// sample 优先查询后绘制的区域，包围盒外跳过整组三角形
+// 入参: index 节点位置, first 起始三角形, end 结束位置, x 横坐标, y 纵坐标
+// 返回: color.RGBA 采样颜色, bool 是否命中
+func (s *MeshSampler) sample(index, first, end int, x, y float64) (color.RGBA, bool) {
+	node := s.nodes[index]
+	if x < node.minX || x > node.maxX || y < node.minY || y > node.maxY {
+		return color.RGBA{}, false
+	}
+	if end-first <= 8 {
+		for i := end - 1; i >= first; i-- {
+			if value, ok := meshTriangleColor(&s.mesh.Triangles[i], x, y); ok {
+				return value, true
+			}
+		}
+		return color.RGBA{}, false
+	}
+	middle := first + (end-first)/2
+	if value, ok := s.sample(node.right, middle, end, x, y); ok {
+		return value, true
+	}
+	return s.sample(index+1, first, middle, x, y)
+}