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// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ofdgo
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import (
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"fmt"
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"image/color"
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"math"
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)
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// GouraudShd 高洛德渐变，按EdgeFlag连接三角形
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type GouraudShd struct {
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Extend int `xml:"Extend,attr,omitempty"`
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Point []ShdPoint `xml:"Point"`
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BackColor *ShdColor `xml:"BackColor,omitempty"`
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}
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// LaGouraudShd 格构高洛德渐变，按行排列控制点
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type LaGouraudShd struct {
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VerticesPerRow int `xml:"VerticesPerRow,attr"`
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Extend int `xml:"Extend,attr,omitempty"`
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Point []ShdPoint `xml:"Point"`
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BackColor *ShdColor `xml:"BackColor,omitempty"`
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}
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// ShdPoint 网格控制点及基本颜色
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type ShdPoint struct {
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X float64 `xml:"X,attr"`
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Y float64 `xml:"Y,attr"`
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EdgeFlag int `xml:"EdgeFlag,attr,omitempty"`
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Color ShdColor `xml:"Color"`
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}
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// MeshVertex 保存局部毫米坐标、原颜色分量及非预乘透明度
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type MeshVertex struct {
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Point Point
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Space string
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Values [4]float64
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Alpha float64
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}
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// MeshShading 保存后端无关的三角网格，后出现的三角形覆盖先出现的三角形
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type MeshShading struct {
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Triangles [][3]MeshVertex
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Background color.RGBA
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}
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// outline 返回方向一致的三角形轮廓，供绘制裁剪和对象度量共用
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// 返回: GeometryPath 非零绕数填充轮廓
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func (m *MeshShading) outline() GeometryPath {
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var path GeometryPath
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for _, t := range m.Triangles {
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a, b, c := t[0].Point, t[1].Point, t[2].Point
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cross := (b.X-a.X)*(c.Y-a.Y) - (b.Y-a.Y)*(c.X-a.X)
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if cross == 0 {
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continue
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}
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if cross < 0 {
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b, c = c, b
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}
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path = append(path, GeometrySegment{Verb: GeometryMove, End: a}, GeometrySegment{Verb: GeometryLine, End: b}, GeometrySegment{Verb: GeometryLine, End: c}, GeometrySegment{Verb: GeometryClose})
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}
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return path
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}
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// resolveMesh 按GB/T 33190的三角形连接规则解析网格
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// 入参: fill 网格颜色
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// 返回: *MeshShading 网格画刷, error 无效控制点
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func (r *Renderer) resolveMesh(fill *FillColor) (*MeshShading, error) {
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var points []ShdPoint
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var back *ShdColor
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var extend, columns int
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if node := fill.GouraudShd; node != nil {
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points, back, extend = node.Point, node.BackColor, node.Extend
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} else {
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node := fill.LaGouraudShd
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points, back, extend, columns = node.Point, node.BackColor, node.Extend, node.VerticesPerRow
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if columns == 0 {
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return nil, fmt.Errorf("invalid lattice shading dimensions")
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}
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}
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indices, err := meshTriangleIndices(points, columns, extend)
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if err != nil {
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return nil, err
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}
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vertices := make([]MeshVertex, len(points))
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for i, point := range points {
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space := point.Color.ColorSpace
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if space == "" {
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space = fill.ColorSpace
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}
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kind, values := r.colorComponents(point.Color.Value, point.Color.Index, space)
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alpha := 1.0
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if value := mergeAlpha(point.Color.Alpha, fill.Alpha); value != nil {
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alpha = float64(*value) / 255
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}
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vertices[i] = MeshVertex{Point{point.X, point.Y}, kind, values, alpha}
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}
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mesh := &MeshShading{}
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if extend == 1 && back != nil {
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space := back.ColorSpace
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if space == "" {
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space = fill.ColorSpace
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}
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mesh.Background = r.ResolveColor(back.Value, back.Index, space, mergeAlpha(back.Alpha, fill.Alpha))
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}
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for _, triangle := range indices {
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mesh.Triangles = append(mesh.Triangles, [3]MeshVertex{vertices[triangle[0]], vertices[triangle[1]], vertices[triangle[2]]})
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}
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for i := range mesh.Triangles {
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t := &mesh.Triangles[i]
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if t[0].Space != t[1].Space || t[0].Space != t[2].Space {
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for j := range t {
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r, g, b := meshRGB(t[j].Space, t[j].Values)
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t[j].Space, t[j].Values = "RGB", [4]float64{r, g, b}
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}
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}
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}
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return mesh, nil
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}
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// meshTriangleIndices 校验控制点并生成共享边或格构三角形编号
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// 入参: points 控制点, columns 每行点数，零表示非格构, extend 延伸标志
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// 返回: [][3]int 三角形顶点编号, error 非法拓扑
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func meshTriangleIndices(points []ShdPoint, columns, extend int) ([][3]int, error) {
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if len(points) < 3 || extend < 0 || extend > 1 {
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return nil, fmt.Errorf("invalid mesh shading")
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}
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if columns != 0 && (columns < 2 || columns > len(points)/2 || len(points)%columns != 0) {
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return nil, fmt.Errorf("invalid lattice shading dimensions")
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}
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for i, p := range points {
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if !finite(p.X) || !finite(p.Y) || p.EdgeFlag < 0 || p.EdgeFlag > 2 {
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return nil, fmt.Errorf("invalid mesh shading point %d", i)
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}
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}
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var result [][3]int
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if columns != 0 {
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for i := columns; i < len(points); i++ {
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if i%columns != 0 {
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result = append(result, [3]int{i - columns - 1, i - columns, i - 1}, [3]int{i - columns, i - 1, i})
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}
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}
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return result, nil
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}
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var triangle [3]int
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for i := 0; i < len(points); {
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switch points[i].EdgeFlag {
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case 0:
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if len(points)-i < 3 {
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return nil, fmt.Errorf("incomplete mesh shading triangle")
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}
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triangle = [3]int{i, i + 1, i + 2}
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i += 3
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case 1, 2:
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if i == 0 {
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return nil, fmt.Errorf("mesh shading starts with a shared edge")
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}
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if points[i].EdgeFlag == 1 {
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triangle[0] = triangle[1]
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}
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triangle[1], triangle[2] = triangle[2], i
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i++
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}
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result = append(result, triangle)
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}
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return result, nil
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}
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// At 按三角形面积权重插值原颜色分量，返回预乘RGBA
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// 入参: x 横坐标, y 纵坐标
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// 返回: color.RGBA 采样颜色
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func (m *MeshShading) At(x, y float64) color.RGBA {
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for i := len(m.Triangles) - 1; i >= 0; i-- {
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t := m.Triangles[i]
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a, b, c := t[0].Point, t[1].Point, t[2].Point
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d := (b.Y-c.Y)*(a.X-c.X) + (c.X-b.X)*(a.Y-c.Y)
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if d == 0 {
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continue
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}
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u := ((b.Y-c.Y)*(x-c.X) + (c.X-b.X)*(y-c.Y)) / d
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v := ((c.Y-a.Y)*(x-c.X) + (a.X-c.X)*(y-c.Y)) / d
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w := 1 - u - v
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if u < -1e-12 || v < -1e-12 || w < -1e-12 {
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continue
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}
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var values [4]float64
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alpha := 0.0
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for j, weight := range [3]float64{u, v, w} {
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alpha += weight * t[j].Alpha
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for k := range values {
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values[k] += weight * t[j].Values[k]
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}
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}
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red, green, blue := meshRGB(t[0].Space, values)
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return color.RGBA{meshByte(red * alpha), meshByte(green * alpha), meshByte(blue * alpha), meshByte(alpha)}
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}
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return m.Background
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}
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// meshRGB 将插值后的颜色分量转换为RGB
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// 入参: space 颜色模型, values 分量
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// 返回: float64 红、绿、蓝分量
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func meshRGB(space string, values [4]float64) (float64, float64, float64) {
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switch space {
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case "GRAY":
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return values[0], values[0], values[0]
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case "CMYK":
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return (1 - values[0]) * (1 - values[3]), (1 - values[1]) * (1 - values[3]), (1 - values[2]) * (1 - values[3])
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default:
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return values[0], values[1], values[2]
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}
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}
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// meshByte 将归一化颜色分量量化为八位整数
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// 入参: value 分量
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// 返回: uint8 量化结果
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func meshByte(value float64) uint8 { return uint8(math.Round(math.Max(0, math.Min(1, value)) * 255)) }
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