// 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"
	"math"

	baseimage "github.com/xiaoqidun/ofdgo/internal/base/image"
	codecpdf "github.com/xiaoqidun/ofdgo/internal/codec/pdf"
	"github.com/xiaoqidun/pdfgo"
)

// pdfCompositePattern 保存图案单元的原始图元和独立几何缓存
type pdfCompositePattern struct {
	nodes           []pdfCompositeNode
	local           pdfImporter
	box             Box
	transferChecked bool
	transferOpaque  bool
}

// pdfShadingSourceKey 区分图案的使用几何及填充或描边
type pdfShadingSourceKey struct {
	pattern  *pdfgo.ShadingPattern
	geometry pdfCompositeKey
}

// tiling 将图案作为非隔离组绘制，保留背景贡献及单元间隙
// 入参: paint 图案画刷, backdrop 初始背景, space 混合空间, channels 可选源通道输出
// 返回: []pdfCompositePixel 去除背景贡献的图案像素, error 解析或绘制错误
func (c *pdfCompositor) tiling(paint pdfgo.Paint, backdrop []pdfCompositePixel, space *pdfgo.ColorSpace, channels []uint8) ([]pdfCompositePixel, error) {
	source := paint.Tiling
	matrix := c.importer.matrix.Mul(source.Matrix)
	inverse, ok := matrix.Inverse()
	if !ok {
		return nil, fmt.Errorf("invalid PDF tiling pattern matrix")
	}
	pattern, err := c.importer.compositePattern(paint)
	if err != nil {
		return nil, err
	}
	xstep, ystep := math.Abs(source.XStep), math.Abs(source.YStep)
	area := pdfBounds([]pdfgo.Point{
		inverse.Apply(pdfgo.Point{X: c.box.X, Y: c.box.Y}), inverse.Apply(pdfgo.Point{X: c.box.X + c.box.W, Y: c.box.Y}),
		inverse.Apply(pdfgo.Point{X: c.box.X + c.box.W, Y: c.box.Y + c.box.H}), inverse.Apply(pdfgo.Point{X: c.box.X, Y: c.box.Y + c.box.H}),
	})
	left, right := math.Ceil((area.X-source.BBox.XMax)/xstep), math.Floor((area.X+area.W-source.BBox.XMin)/xstep)
	top, bottom := math.Ceil((area.Y-source.BBox.YMax)/ystep), math.Floor((area.Y+area.H-source.BBox.YMin)/ystep)
	limit := float64(int(^uint(0) >> 1))
	for _, value := range []float64{left, right, top, bottom} {
		if !finite(value) || value <= -limit || value >= limit {
			return nil, fmt.Errorf("PDF tiling pattern instance range overflow")
		}
	}
	result := c.acquirePixels(len(backdrop))
	complete := false
	defer func() {
		if !complete {
			c.releasePixels(result)
		}
	}()
	for i, pixel := range backdrop {
		if i%pdfCompositeTileSize == 0 {
			if err := c.importer.ctx.Err(); err != nil {
				return nil, err
			}
		}
		result[i] = pdfCompositePixel{Values: pixel.Values, Alpha: pixel.Alpha}
	}
	candidate := c.acquirePixels(len(backdrop))
	defer c.releasePixels(candidate)
	var candidateChannels []uint8
	if channels != nil {
		candidateChannels = c.acquireChannels(len(backdrop))
		defer c.releaseChannels(candidateChannels)
	}
	disjoint := source.BBox.XMax-source.BBox.XMin <= xstep && source.BBox.YMax-source.BBox.YMin <= ystep
	pixelStep := 25.4 / c.importer.rasterDPI
	localInverse, _ := pattern.local.matrix.Inverse()
	for row := int(top); row <= int(bottom); row++ {
		for column := int(left); column <= int(right); column++ {
			if err := c.importer.ctx.Err(); err != nil {
				return nil, err
			}
			x, y := float64(column)*xstep, float64(row)*ystep
			dx, dy := matrix[0]*x+matrix[2]*y+pattern.box.X, matrix[1]*x+matrix[3]*y+pattern.box.Y
			left := int(math.Max(0, math.Min(float64(c.width), math.Floor((dx-c.box.X)/pixelStep)-1)))
			right := int(math.Max(0, math.Min(float64(c.width), math.Ceil((dx+pattern.box.W-c.box.X)/pixelStep)+1)))
			top := int(math.Max(0, math.Min(float64(c.height), math.Floor((dy-c.box.Y)/pixelStep)-1)))
			bottom := int(math.Max(0, math.Min(float64(c.height), math.Ceil((dy+pattern.box.H-c.box.Y)/pixelStep)+1)))
			width, height := right-left, bottom-top
			if width <= 0 || height <= 0 {
				continue
			}
			pixels := candidate[:width*height]
			var cellChannels []uint8
			if channels != nil {
				cellChannels = candidateChannels[:width*height]
			}
			for y := range height {
				if err := c.importer.ctx.Err(); err != nil {
					return nil, err
				}
				for x := range width {
					index := (top+y)*c.width + left + x
					initial := result[index]
					if disjoint {
						initial = backdrop[index]
					}
					pixels[y*width+x] = pdfCompositePixel{Values: initial.Values, Alpha: initial.Alpha}
					if cellChannels != nil {
						cellChannels[y*width+x] = 0
						if !disjoint {
							cellChannels[y*width+x] = channels[index]
						}
					}
				}
			}
			cell := pdfCompositor{importer: &pattern.local, box: Box{X: c.box.X + float64(left)*pixelStep - dx, Y: c.box.Y + float64(top)*pixelStep - dy, W: float64(width) * pixelStep, H: float64(height) * pixelStep},
				width: width, height: height, inverse: localInverse, cache: pattern.local.compositingCache(), scratch: c.scratch, origins: c.origins, masks: map[*pdfgo.SoftMask][]float64{}, softMask: c.softMask, channels: cellChannels}
			err := cell.draw(pattern.nodes, pixels, space)
			cell.releaseMasks()
			if err != nil {
				return nil, err
			}
			for y := range height {
				if err := c.importer.ctx.Err(); err != nil {
					return nil, err
				}
				for x := range width {
					index := (top+y)*c.width + left + x
					pdfCompositePatternCell(&result[index], backdrop[index], pixels[y*width+x], disjoint)
					if channels != nil && pixels[y*width+x].Shape != 0 {
						if disjoint {
							channels[index] |= cellChannels[y*width+x]
						} else {
							channels[index] = cellChannels[y*width+x]
						}
					}
				}
			}
		}
	}
	for i := range result {
		if i%pdfCompositeTileSize == 0 {
			if err := c.importer.ctx.Err(); err != nil {
				return nil, err
			}
		}
		pixel := &result[i]
		if pixel.Effect != 0 {
			for j := 0; j < space.Components(); j++ {
				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))
			}
		}
		pixel.Alpha = pixel.Effect
	}
	complete = true
	return result, nil
}

// pdfCompositePatternCell 合并互不重叠单元的覆盖贡献，避免相邻抗锯齿边缘重复混合
// 入参: target 图案累计结果, initial 原始背景, source 单元结果, disjoint 单元边界是否互不重叠
func pdfCompositePatternCell(target *pdfCompositePixel, initial, source pdfCompositePixel, disjoint bool) {
	if source.Shape == 0 {
		return
	}
	if disjoint {
		alpha := math.Max(0, math.Min(1, target.Alpha+source.Alpha-initial.Alpha))
		if alpha != 0 {
			for i := range target.Values {
				target.Values[i] = (target.Values[i]*target.Alpha + source.Values[i]*source.Alpha - initial.Values[i]*initial.Alpha) / alpha
			}
		}
		target.Alpha = alpha
		target.Effect = math.Min(1, target.Effect+source.Effect)
		target.Shape = math.Min(1, target.Shape+source.Shape)
	} else {
		target.Values, target.Alpha = source.Values, source.Alpha
		target.Effect += source.Effect * (1 - target.Effect)
		target.Shape += source.Shape * (1 - target.Shape)
	}
}

// compositePattern 复用图案单元解析及几何上下文，供检查和局部合成共同使用
// 入参: paint 图案画刷
// 返回: *pdfCompositePattern 单元内容, error 解析或边界错误
func (p *pdfImporter) compositePattern(paint pdfgo.Paint) (*pdfCompositePattern, error) {
	paint.Alpha = 1
	cache := p.compositingCache()
	if cache.patterns == nil {
		cache.patterns = make(map[pdfgo.Paint]*pdfCompositePattern)
	}
	if pattern := cache.patterns[paint]; pattern != nil {
		return pattern, nil
	}
	source := paint.Tiling
	nodes, err := p.collectCompositeNodes(func(v pdfgo.Visitor) error { return source.Walk(p.ctx, paint, v) }, false)
	if err != nil {
		return nil, err
	}
	matrix := p.matrix.Mul(source.Matrix)
	b := source.BBox
	box := pdfBounds([]pdfgo.Point{
		matrix.Apply(pdfgo.Point{X: b.XMin, Y: b.YMin}), matrix.Apply(pdfgo.Point{X: b.XMax, Y: b.YMin}),
		matrix.Apply(pdfgo.Point{X: b.XMax, Y: b.YMax}), matrix.Apply(pdfgo.Point{X: b.XMin, Y: b.YMax}),
	})
	if box.W <= 0 || box.H <= 0 {
		return nil, fmt.Errorf("invalid PDF tiling pattern bounds")
	}
	local := *p
	local.matrix = matrix
	local.matrix[4] -= box.X
	local.matrix[5] -= box.Y
	local.pageWidth, local.pageHeight = box.W, box.H
	local.compositeCache = nil
	local.compositingCache().geometry = cache.geometryCache()
	local.compositingCache().clips = cache.clipCache()
	pattern := &pdfCompositePattern{nodes: nodes, local: local, box: box}
	cache.patterns[paint] = pattern
	return pattern, nil
}

// directCompositeNode 检查图元、透明组和图案单元能否独立保留，逐层核对背景混合
// 入参: node 图元, space 混合空间
// 返回: bool 是否可直接转换, error 图案或遮罩解析错误
func (p *pdfImporter) directCompositeNode(node pdfCompositeNode, space *pdfgo.ColorSpace) (bool, error) {
	if node.group == nil && space.Device() {
		style, fill, stroke := node.style()
		if node.image == nil || node.image.Image.ImageMask {
			for i, paint := range [2]pdfgo.Paint{style.Fill, style.Stroke} {
				if i == 0 && !fill || i == 1 && !stroke {
					continue
				}
				if native := codecpdf.PrepareShadingColorants(paint, space, false); native != nil {
					if !native.Process.AlternateEquivalent() || i == 0 && style.FillOverprint || i == 1 && style.StrokeOverprint {
						return false, nil
					}
				}
			}
		}
		if space.Model == "DeviceCMYK" && style.ColorConversion != (pdfgo.ColorConversion{}) {
			if node.image != nil && !node.image.Image.ImageMask {
				_, native, err := codecpdf.ImageProcessColorants(node.image.Image)
				if err != nil {
					return false, err
				}
				if !native {
					source := p.compositingCache().images[node.image.Image]
					if source == nil {
						source, err = node.image.Image.DecodeComponentsViewContext(p.ctx)
						if err != nil {
							return false, err
						}
						p.compositingCache().images[node.image.Image] = source
					}
					if source.Space.Model == "DeviceRGB" && source.Space.Device() {
						return false, nil
					}
				}
			} else {
				for i, paint := range [2]pdfgo.Paint{style.Fill, style.Stroke} {
					if i == 0 && !fill || i == 1 && !stroke || paint.None || paint.Tiling != nil {
						continue
					}
					source := paint.Space
					switch {
					case paint.Axial != nil:
						source = paint.Axial.Space
					case paint.Radial != nil:
						source = paint.Radial.Space
					case paint.Function != nil:
						source = paint.Function.Space
					case paint.Mesh != nil:
						source = paint.Mesh.Space
					}
					if source != nil && source.Model == "DeviceRGB" && source.Device() || source == nil && paint.CMYK == nil && paint.SourceSpace != "DeviceGray" {
						return false, nil
					}
				}
			}
		}
	}
	directGroup := false
	if group := node.group; group != nil && !group.Knockout && group.Alpha == 1 && group.SoftMask == nil && codecpdf.NormalBlend(group.BlendMode) && (group.ColorSpace == nil || group.ColorSpace.SRGBEquivalent()) {
		directGroup = true
	}
	opaque, err := p.opaque(node, space)
	if err != nil {
		return false, err
	}
	if !opaque && !(space.SRGBEquivalent() && (directGroup || node.direct())) {
		if node.textObject != nil && space.SRGBEquivalent() {
			for _, child := range node.children {
				if direct, err := p.directCompositeNode(child, space); err != nil || !direct {
					return direct, err
				}
			}
			return p.disjointText(node)
		}
		return false, nil
	}
	if node.group != nil {
		for _, child := range node.children {
			if direct, err := p.directCompositeNode(child, space); err != nil || !direct {
				return direct, err
			}
		}
		return true, nil
	}
	if node.image != nil && !node.image.Image.ImageMask {
		return true, nil
	}
	style, fill, stroke := node.style()
	for i, paint := range []pdfgo.Paint{style.Fill, style.Stroke} {
		if i == 0 && !fill || i == 1 && !stroke || paint.Tiling == nil {
			continue
		}
		pattern, err := p.compositePattern(paint)
		if err != nil {
			return false, err
		}
		for _, child := range pattern.nodes {
			if direct, err := pattern.local.directCompositeNode(child, space); err != nil || !direct {
				return direct, err
			}
		}
	}
	return true, nil
}

// processOverprint 检查图元、透明组和图案单元是否需要设备四色套印
// 入参: nodes 原始图元
// 返回: bool 是否需要四色混合, error 图像或图案解析错误
func (p *pdfImporter) processOverprint(nodes []pdfCompositeNode) (bool, error) {
	for _, node := range nodes {
		if node.group != nil {
			if found, err := p.processOverprint(node.children); err != nil || found {
				return found, err
			}
			continue
		}
		style, fill, stroke := node.style()
		if node.image != nil && style.FillOverprint {
			if _, found, err := codecpdf.ImageProcessColorants(node.image.Image); err != nil || found {
				return found, err
			}
		}
		if node.image != nil && !node.image.Image.ImageMask {
			continue
		}
		if fill && style.FillOverprint && codecpdf.OverprintNeedsSeparation(style.Fill) || stroke && style.StrokeOverprint && codecpdf.OverprintNeedsSeparation(style.Stroke) {
			return true, nil
		}
		if style.Transfer != nil || style.Halftone != nil {
			if fill && style.FillOverprint && style.Fill.CMYK != nil || stroke && style.StrokeOverprint && style.Stroke.CMYK != nil {
				transfer, err := p.resolveTransfer(style, "DeviceCMYK")
				if err != nil || transfer != nil {
					return transfer != nil, err
				}
			}
		}
		for i, paint := range []pdfgo.Paint{style.Fill, style.Stroke} {
			if i == 0 && fill && style.FillOverprint || i == 1 && stroke && style.StrokeOverprint {
				if native := codecpdf.PrepareShadingColorants(paint, &pdfgo.ColorSpace{Model: "DeviceCMYK"}, false); native != nil {
					return true, nil
				}
				native, _, err := codecpdf.NativePaint(paint, &pdfgo.ColorSpace{Model: "DeviceCMYK"}, style.RenderingIntent)
				if err != nil {
					return false, err
				}
				if native != nil && (!codecpdf.OpaqueBlack(*native) || !codecpdf.OpaqueBlack(paint)) {
					return true, nil
				}
			}
			if paint.Shading != nil && (i == 0 && fill || i == 1 && stroke) {
				nodes, err := p.compositeShadingPattern(paint.Shading)
				if err != nil {
					return false, err
				}
				if found, err := p.processOverprint(nodes); err != nil || found {
					return found, err
				}
			}
			if i == 0 && !fill || i == 1 && !stroke || paint.Tiling == nil {
				continue
			}
			pattern, err := p.compositePattern(paint)
			if err != nil {
				return false, err
			}
			if found, err := pattern.local.processOverprint(pattern.nodes); err != nil || found {
				return found, err
			}
		}
	}
	return false, nil
}

// resolveTransfer 无设备函数时保留无缓存快速路径，按需绑定单页解析缓存
// 入参: style 原始图形状态, model 原生设备颜色空间
// 返回: *pdfgo.TransferFunction 有效函数, error 网屏传递函数错误
func (p *pdfImporter) resolveTransfer(style pdfgo.Style, model pdfgo.Name) (*pdfgo.TransferFunction, error) {
	if style.Halftone == nil && style.Transfer == nil {
		return nil, nil
	}
	return p.compositingCache().transfers.Resolve(p.reader, style, model)
}

// compositeHasTransfer 检查最终设备使用的通道，不将备用通道误判为有效函数
// 入参: nodes 原始图元及透明组, model 原生设备颜色空间
// 返回: bool 是否存在非恒等函数, error 网屏函数错误
func (p *pdfImporter) compositeHasTransfer(nodes []pdfCompositeNode, model pdfgo.Name) (bool, error) {
	for _, node := range nodes {
		if node.group != nil {
			if found, err := p.compositeHasTransfer(node.children, model); err != nil || found {
				return found, err
			}
		} else {
			style, _, _ := node.style()
			transfer, err := p.resolveTransfer(style, model)
			if err != nil || transfer != nil {
				return transfer != nil, err
			}
		}
	}
	return false, nil
}

// transferDevice 为四色叠印保留原生设备通道，其余页面使用连续RGB设备
// 入参: space 页面混合空间, nodes 参与合成的图元
// 返回: pdfgo.Name 原生设备空间, error 图案或图像解析错误
func (p *pdfImporter) transferDevice(space *pdfgo.ColorSpace, nodes []pdfCompositeNode) (pdfgo.Name, error) {
	if space.Model == "DeviceCMYK" && !space.Calibrated() {
		if found, err := p.processOverprint(nodes); err != nil {
			return "", err
		} else if found {
			return "DeviceCMYK", nil
		}
	}
	return "DeviceRGB", nil
}

// selectTransfer 按最上层基本图元及祖先的不透明状态选择最终设备函数
// 入参: node 基本图元, outline 是否描边
// 返回: *pdfgo.TransferFunction 当前函数或设备默认值, error 图案解析错误
func (c *pdfCompositor) selectTransfer(node pdfCompositeNode, outline bool) (*pdfgo.TransferFunction, error) {
	style, _, _ := node.style()
	paint := style.Fill
	if outline {
		paint = style.Stroke
	}
	if c.transferBlocked || paint.Alpha != 1 || style.SoftMask != nil || !codecpdf.NormalBlend(style.BlendMode) {
		return nil, nil
	}
	transfer, err := c.importer.resolveTransfer(style, c.transferModel)
	if err != nil || transfer == nil {
		return transfer, err
	}
	if pattern := paint.Shading; pattern != nil && (node.image == nil || node.image.Image.ImageMask) {
		inner := pattern.Style
		if inner.Fill.Alpha != 1 || inner.SoftMask != nil || !codecpdf.NormalBlend(inner.BlendMode) {
			return nil, nil
		}
	}
	if node.image != nil {
		soft, err := node.image.Image.HasSoftMask()
		if err != nil || soft {
			return nil, err
		}
	}
	if paint.Tiling != nil && (node.image == nil || node.image.Image.ImageMask) {
		pattern, err := c.importer.compositePattern(paint)
		if err != nil {
			return nil, err
		}
		opaque, err := pattern.opaqueTransfer()
		if err != nil || !opaque {
			return nil, err
		}
	}
	return transfer, nil
}

// opaqueTransfer 复用图案不透明性检查，图案内部函数不提前作用于源颜色
// 返回: bool 是否允许使用外层设备函数, error 单元解析错误
func (p *pdfCompositePattern) opaqueTransfer() (bool, error) {
	if !p.transferChecked {
		for _, child := range p.nodes {
			opaque, err := p.local.transferOpaque(child)
			if err != nil {
				return false, err
			}
			if !opaque {
				p.transferChecked = true
				return false, nil
			}
		}
		p.transferChecked, p.transferOpaque = true, true
	}
	return p.transferOpaque, nil
}

// transferOpaque 检查全部图案内容的不透明条件，不限制混合颜色空间
// 入参: node 单元图元或透明组
// 返回: bool 是否不透明, error 图案或图片遮罩引用错误
func (p *pdfImporter) transferOpaque(node pdfCompositeNode) (bool, error) {
	if group := node.group; group != nil {
		if group.Alpha != 1 || group.SoftMask != nil || !codecpdf.NormalBlend(group.BlendMode) {
			return false, nil
		}
		for _, child := range node.children {
			if opaque, err := p.transferOpaque(child); err != nil || !opaque {
				return opaque, err
			}
		}
		return true, nil
	}
	style, fill, stroke := node.style()
	if style.SoftMask != nil || !codecpdf.NormalBlend(style.BlendMode) || fill && style.Fill.Alpha != 1 || stroke && style.Stroke.Alpha != 1 {
		return false, nil
	}
	if node.image != nil {
		soft, err := node.image.Image.HasSoftMask()
		if err != nil || soft {
			return false, err
		}
		if !node.image.Image.ImageMask {
			return true, nil
		}
	}
	for i, paint := range [2]pdfgo.Paint{style.Fill, style.Stroke} {
		if pattern := paint.Shading; pattern != nil && (i == 0 && fill || i == 1 && stroke) {
			inner := pattern.Style
			if inner.Fill.Alpha != 1 || inner.SoftMask != nil || !codecpdf.NormalBlend(inner.BlendMode) {
				return false, nil
			}
		}
		if i == 0 && !fill || i == 1 && !stroke || paint.Tiling == nil {
			continue
		}
		pattern, err := p.compositePattern(paint)
		if err != nil {
			return false, err
		}
		if opaque, err := pattern.opaqueTransfer(); err != nil || !opaque {
			return opaque, err
		}
	}
	return true, nil
}

// halftone 检查连续色调转换，避免将打印网屏误用于屏幕显示
// 入参: style 图形状态
// 返回: error 严格模式无法保留设备网屏
func (p *pdfImporter) halftone(style pdfgo.Style) error {
	h := style.Halftone
	message := "PDF continuous-tone appearance retained; device halftone not transferred to OFD"
	if h == nil || h.Type == 0 {
		if style.HalftoneOrigin == nil {
			return nil
		}
		message = "PDF continuous-tone appearance retained; device halftone origin not transferred to OFD"
	}
	if p.warning == nil {
		return &pdfgo.UnsupportedError{Feature: "device halftone conversion"}
	}
	if p.halftoneWarnings == nil {
		p.halftoneWarnings = make(map[*pdfgo.Halftone]bool)
	}
	if !p.halftoneWarnings[h] {
		p.halftoneWarnings[h] = true
		p.warning(pdfgo.Diagnostic{Message: message})
	}
	return nil
}

// compositeShadingPattern 在页面内复用图案内部图元，不缓存依赖背景的像素
// 入参: pattern 只读着色图案
// 返回: []pdfCompositeNode 隐式挖空组, error 遍历或资源错误
func (p *pdfImporter) compositeShadingPattern(pattern *pdfgo.ShadingPattern) ([]pdfCompositeNode, error) {
	cache := p.compositingCache()
	if nodes, found := cache.shadingPatterns[pattern]; found {
		return nodes, nil
	}
	inverse, ok := p.matrix.Inverse()
	if !ok {
		return nil, &pdfgo.UnsupportedError{Feature: "shading pattern page transform"}
	}
	box := pdfBounds([]pdfgo.Point{
		inverse.Apply(pdfgo.Point{}), inverse.Apply(pdfgo.Point{X: p.pageWidth}),
		inverse.Apply(pdfgo.Point{X: p.pageWidth, Y: p.pageHeight}), inverse.Apply(pdfgo.Point{Y: p.pageHeight}),
	})
	nodes, err := p.collectCompositeNodes(func(visitor pdfgo.Visitor) error {
		return pattern.Walk(p.ctx, pdfgo.Rectangle{XMin: box.X, YMin: box.Y, XMax: box.X + box.W, YMax: box.Y + box.H}, visitor)
	}, false)
	if err != nil {
		return nil, err
	}
	if cache.shadingPatterns == nil {
		cache.shadingPatterns = make(map[*pdfgo.ShadingPattern][]pdfCompositeNode)
	}
	cache.shadingPatterns[pattern] = nodes
	return nodes, nil
}

// 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
// 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, channels 可选源通道输出
// 返回: []pdfCompositePixel 源颜色、形状及不透明度, error 状态或合成错误
func (c *pdfCompositor) shadingPattern(pattern *pdfgo.ShadingPattern, node pdfCompositeNode, outline bool, backdrop []pdfCompositePixel, space *pdfgo.ColorSpace, channels []uint8) ([]pdfCompositePixel, error) {
	nodes, err := c.importer.shadingSources(pattern, node, outline)
	if err != nil {
		return nil, err
	}
	local := *c
	local.transfers, local.shadingSource = nil, true
	local.channels = channels
	result, err := local.shadingSourcePixels(nodes[len(nodes)-1], backdrop, space)
	if err != nil || len(nodes) == 1 {
		return result, err
	}
	var backgroundChannels []uint8
	if channels != nil {
		backgroundChannels = c.acquireChannels(len(channels))
		defer c.releaseChannels(backgroundChannels)
		clear(backgroundChannels)
	}
	local.channels = backgroundChannels
	background, err := local.shadingSourcePixels(nodes[0], backdrop, space)
	if err != nil {
		c.releasePixels(result)
		return nil, err
	}
	defer c.releasePixels(background)
	coverage, err := c.coverage(nodes[0], outline)
	if err != nil {
		c.releasePixels(result)
		return nil, err
	}
	defer c.releaseCoverage(coverage)
	step := 25.4 / c.importer.rasterDPI
	for i := range result {
		if i%pdfCompositeTileSize == 0 {
			if err := c.importer.ctx.Err(); err != nil {
				c.releasePixels(result)
				return nil, err
			}
		}
		shape := 0.0
		if coverage != nil {
			a := baseimage.AlphaAt(coverage, i%c.width, i/c.width)
			shape = float64(a) / 65535
		}
		if nodes[0].image != nil && shape != 0 {
			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})
			_, alpha, err := c.imageColor(nodes[0].image, point, space)
			if err != nil {
				c.releasePixels(result)
				return nil, err
			}
			shape *= alpha
		}
		remaining := 1.0
		if shape != 0 {
			remaining -= math.Min(1, result[i].Shape/shape)
		}
		alpha := result[i].Alpha + background[i].Alpha*remaining
		if alpha != 0 {
			for j := 0; j < space.Components(); j++ {
				result[i].Values[j] = (result[i].Values[j]*result[i].Alpha + background[i].Values[j]*background[i].Alpha*remaining) / alpha
			}
		}
		result[i].Alpha, result[i].Effect = alpha, alpha
		result[i].Shape += background[i].Shape * remaining
		if channels != nil && background[i].Shape*remaining > 0 {
			channels[i] |= backgroundChannels[i]
		}
	}
	return result, nil
}

// shadingSources 将内部状态绑定到使用图元，几何和裁剪仅计算一次
// 入参: pattern 只读着色图案, node 使用图元, outline 是否描边
// 返回: []pdfCompositeNode 背景及着色图元, error 图案遍历错误
func (p *pdfImporter) shadingSources(pattern *pdfgo.ShadingPattern, node pdfCompositeNode, outline bool) ([]pdfCompositeNode, error) {
	cache := p.compositingCache()
	key := pdfShadingSourceKey{pattern, pdfCompositeKey{path: node.path, text: node.text, image: node.image, stroke: outline}}
	if sources, ok := cache.shadingSources[key]; ok {
		return sources, nil
	}
	nodes, err := p.compositeShadingPattern(pattern)
	if err != nil {
		return nil, err
	}
	outer, _, _ := node.style()
	sources := make([]pdfCompositeNode, 0, len(nodes[0].children))
	for _, child := range nodes[0].children {
		style := child.path.Style
		style.LineWidth, style.Cap, style.Join, style.MiterLimit = outer.LineWidth, outer.Cap, outer.Join, outer.MiterLimit
		style.Dash, style.DashPhase, style.StrokeAdjust = outer.Dash, outer.DashPhase, outer.StrokeAdjust
		style.Clips = append(append([]pdfgo.Path(nil), outer.Clips...), style.Clips...)
		style.Stroke, style.StrokeOverprint = style.Fill, style.FillOverprint
		source := node
		if node.path != nil {
			mark := *node.path
			mark.Style, mark.Fill, mark.Stroke = style, !outline, outline
			source.path = &mark
		} else if node.text != nil {
			mark := *node.text
			mark.Style, mark.Mode = style, 0
			if outline {
				mark.Mode = 1
			}
			source.text = &mark
		} else {
			mark := *node.image
			mark.Style = style
			source.image = &mark
		}
		sources = append(sources, source)
	}
	if cache.shadingSources == nil {
		cache.shadingSources = make(map[pdfShadingSourceKey][]pdfCompositeNode)
	}
	cache.shadingSources[key] = sources
	return sources, nil
}

// shadingSourcePixels 求值单个内部图元并移除初始背景贡献
// 入参: node 内部图元, backdrop 初始背景, space 混合空间
// 返回: []pdfCompositePixel 源颜色和覆盖, error 合成或取消错误
func (c *pdfCompositor) shadingSourcePixels(node pdfCompositeNode, backdrop []pdfCompositePixel, space *pdfgo.ColorSpace) ([]pdfCompositePixel, error) {
	result := c.acquirePixels(len(backdrop))
	complete := false
	defer func() {
		if !complete {
			c.releasePixels(result)
		}
	}()
	for i, pixel := range backdrop {
		result[i] = pdfCompositePixel{Values: pixel.Values, Alpha: pixel.Alpha}
	}
	if err := c.drawMark(node, result, space); err != nil {
		return nil, err
	}
	for i := range result {
		if i%pdfCompositeTileSize == 0 {
			if err := c.importer.ctx.Err(); err != nil {
				return nil, err
			}
		}
		pixel := &result[i]
		if pixel.Effect != 0 {
			for j := 0; j < space.Components(); j++ {
				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))
			}
		}
		pixel.Alpha = pixel.Effect
	}
	complete = true
	return result, nil
}