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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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"math"
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"github.com/xiaoqidun/pdfgo"
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)
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// pdfShadingSourceKey 区分图案的使用几何及填充或描边
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type pdfShadingSourceKey struct {
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pattern *pdfgo.ShadingPattern
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geometry pdfCompositeKey
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}
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// compositeShadingPattern 在页面内复用图案内部图元，不缓存依赖背景的像素
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// 入参: pattern 只读着色图案
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// 返回: []pdfCompositeNode 隐式挖空组, error 遍历或资源错误
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func (p *pdfImporter) compositeShadingPattern(pattern *pdfgo.ShadingPattern) ([]pdfCompositeNode, error) {
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cache := p.compositingCache()
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if nodes, found := cache.shadingPatterns[pattern]; found {
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return nodes, nil
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}
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inverse, ok := p.matrix.Inverse()
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if !ok {
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return nil, &pdfgo.UnsupportedError{Feature: "shading pattern page transform"}
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}
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box := pdfBounds([]pdfgo.Point{
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inverse.Apply(pdfgo.Point{}), inverse.Apply(pdfgo.Point{X: p.pageWidth}),
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inverse.Apply(pdfgo.Point{X: p.pageWidth, Y: p.pageHeight}), inverse.Apply(pdfgo.Point{Y: p.pageHeight}),
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})
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nodes, err := p.collectCompositeNodes(func(visitor pdfgo.Visitor) error {
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return pattern.Walk(p.ctx, pdfgo.Rectangle{XMin: box.X, YMin: box.Y, XMax: box.X + box.W, YMax: box.Y + box.H}, visitor)
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})
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if err != nil {
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return nil, err
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}
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if cache.shadingPatterns == nil {
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cache.shadingPatterns = make(map[*pdfgo.ShadingPattern][]pdfCompositeNode)
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}
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cache.shadingPatterns[pattern] = nodes
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return nodes, nil
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}
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// shadingPattern 统一对象和图案的几何覆盖，按相交面积合成背景及内部着色
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// 入参: pattern 着色图案, node 使用图元, outline 是否描边, backdrop 初始背景, space 父级混合空间
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// 返回: []pdfCompositePixel 源颜色、形状及不透明度, error 状态或合成错误
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func (c *pdfCompositor) shadingPattern(pattern *pdfgo.ShadingPattern, node pdfCompositeNode, outline bool, backdrop []pdfCompositePixel, space *pdfgo.ColorSpace) ([]pdfCompositePixel, error) {
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nodes, err := c.importer.shadingSources(pattern, node, outline)
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if err != nil {
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return nil, err
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}
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local := *c
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local.transfers, local.shadingSource = nil, true
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result, err := local.shadingSourcePixels(nodes[len(nodes)-1], backdrop, space)
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if err != nil || len(nodes) == 1 {
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return result, err
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}
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background, err := local.shadingSourcePixels(nodes[0], backdrop, space)
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if err != nil {
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c.releasePixels(result)
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return nil, err
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}
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defer c.releasePixels(background)
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coverage, err := c.coverage(nodes[0], outline)
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if err != nil {
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c.releasePixels(result)
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return nil, err
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}
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step := 25.4 / c.importer.rasterDPI
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for i := range result {
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if i%pdfCompositeTileSize == 0 {
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if err := c.importer.ctx.Err(); err != nil {
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c.releasePixels(result)
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return nil, err
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}
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}
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shape := 0.0
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if coverage != nil {
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_, _, _, a := coverage.At(i%c.width, i/c.width).RGBA()
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shape = float64(a) / 65535
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}
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if nodes[0].image != nil && shape != 0 {
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point := c.inverse.Apply(pdfgo.Point{X: c.box.X + (float64(i%c.width)+.5)*step, Y: c.box.Y + (float64(i/c.width)+.5)*step})
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_, alpha, err := c.imageColor(nodes[0].image, point, space)
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if err != nil {
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c.releasePixels(result)
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return nil, err
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}
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shape *= alpha
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}
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remaining := 1.0
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if shape != 0 {
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remaining -= math.Min(1, result[i].shape/shape)
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}
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alpha := result[i].alpha + background[i].alpha*remaining
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if alpha != 0 {
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for j := 0; j < space.Components(); j++ {
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result[i].values[j] = (result[i].values[j]*result[i].alpha + background[i].values[j]*background[i].alpha*remaining) / alpha
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}
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}
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result[i].alpha, result[i].effect = alpha, alpha
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result[i].shape += background[i].shape * remaining
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}
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return result, nil
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}
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// shadingSources 将内部状态绑定到使用图元，几何和裁剪仅计算一次
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// 入参: pattern 只读着色图案, node 使用图元, outline 是否描边
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// 返回: []pdfCompositeNode 背景及着色图元, error 图案遍历错误
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func (p *pdfImporter) shadingSources(pattern *pdfgo.ShadingPattern, node pdfCompositeNode, outline bool) ([]pdfCompositeNode, error) {
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cache := p.compositingCache()
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key := pdfShadingSourceKey{pattern, pdfCompositeKey{path: node.path, text: node.text, image: node.image, stroke: outline}}
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if sources, ok := cache.shadingSources[key]; ok {
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return sources, nil
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}
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nodes, err := p.compositeShadingPattern(pattern)
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if err != nil {
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return nil, err
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}
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outer, _, _ := node.style()
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sources := make([]pdfCompositeNode, 0, len(nodes[0].children))
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for _, child := range nodes[0].children {
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style := child.path.Style
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style.LineWidth, style.Cap, style.Join, style.MiterLimit = outer.LineWidth, outer.Cap, outer.Join, outer.MiterLimit
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style.Dash, style.DashPhase, style.StrokeAdjust = outer.Dash, outer.DashPhase, outer.StrokeAdjust
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style.Clips = append(append([]pdfgo.Path(nil), outer.Clips...), style.Clips...)
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style.Stroke, style.StrokeOverprint = style.Fill, style.FillOverprint
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source := node
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if node.path != nil {
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mark := *node.path
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mark.Style, mark.Fill, mark.Stroke = style, !outline, outline
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source.path = &mark
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} else if node.text != nil {
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mark := *node.text
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mark.Style, mark.Mode = style, 0
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if outline {
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mark.Mode = 1
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}
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source.text = &mark
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} else {
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mark := *node.image
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mark.Style = style
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source.image = &mark
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}
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sources = append(sources, source)
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}
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if cache.shadingSources == nil {
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cache.shadingSources = make(map[pdfShadingSourceKey][]pdfCompositeNode)
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}
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cache.shadingSources[key] = sources
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return sources, nil
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}
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// shadingSourcePixels 求值单个内部图元并移除初始背景贡献
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// 入参: node 内部图元, backdrop 初始背景, space 混合空间
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// 返回: []pdfCompositePixel 源颜色和覆盖, error 合成或取消错误
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func (c *pdfCompositor) shadingSourcePixels(node pdfCompositeNode, backdrop []pdfCompositePixel, space *pdfgo.ColorSpace) ([]pdfCompositePixel, error) {
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result := c.acquirePixels(len(backdrop))
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complete := false
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defer func() {
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if !complete {
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c.releasePixels(result)
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}
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}()
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for i, pixel := range backdrop {
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result[i] = pdfCompositePixel{values: pixel.values, alpha: pixel.alpha}
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}
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if err := c.drawMark(node, result, space); err != nil {
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return nil, err
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}
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for i := range result {
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if i%pdfCompositeTileSize == 0 {
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if err := c.importer.ctx.Err(); err != nil {
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return nil, err
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}
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}
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pixel := &result[i]
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if pixel.effect != 0 {
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for j := 0; j < space.Components(); j++ {
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pixel.values[j] = math.Max(0, math.Min(1, (pixel.values[j]*pixel.alpha-backdrop[i].values[j]*backdrop[i].alpha*(1-pixel.effect))/pixel.effect))
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}
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}
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pixel.alpha = pixel.effect
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}
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complete = true
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return result, nil
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}
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