ofdgo/ofdgo_paint.go

// 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"
	"image/color"
	"math"
	"slices"
	"strconv"
	"strings"
)

// PatternPaint 底纹画刷
type PatternPaint struct {
	*Pattern
	Color FillColor
	Alpha *int
}

// ResolveColor 按文档颜色空间和调色板解析颜色，返回预乘透明度的RGBA
// 入参: value 颜色分量, index 调色板索引, space 颜色空间标识, alpha 透明度
// 返回: color.RGBA 标准颜色, error 颜色定义或配置错误
func (r *Renderer) ResolveColor(value string, index *int, space string, alpha *int) (color.RGBA, error) {
	kind, values, err := r.colorComponents(value, index, space)
	if err != nil {
		return color.RGBA{}, err
	}
	if alpha != nil && (*alpha < 0 || *alpha > 255) {
		return color.RGBA{}, fmt.Errorf("color alpha must be between 0 and 255")
	}
	profile, err := r.Reader.colorProfile(r.colorDefinition(space))
	if err != nil {
		return color.RGBA{}, err
	}
	rgb, err := displayColor(kind, values, profile)
	if err != nil {
		return color.RGBA{}, err
	}
	a := 1.0
	if alpha != nil {
		a = float64(*alpha) / 255
	}
	return profileColor(rgb, a), nil
}

// GradientStops 解析OFD渐变分段的位置与透明度，返回独立数据并保留原分段顺序
// 入参: segments 渐变分段, alpha 透明度
// 返回: []ColorStop 后端无关的渐变色标, error 颜色定义或配置错误
func (r *Renderer) GradientStops(segments []ShdSegment, alpha *int) ([]ColorStop, error) {
	var gradient []ColorStop
	positions := gradientPositions(segments)
	for i, segment := range segments {
		segmentAlpha := mergeAlpha(segment.Color.Alpha, alpha)
		value, err := r.ResolveColor(segment.Color.Value, segment.Color.Index, segment.Color.ColorSpace, segmentAlpha)
		if err != nil {
			return nil, err
		}
		gradient = append(gradient, ColorStop{Offset: positions[i], Color: value})
	}
	return gradient, nil
}

// parseColorWithAlpha 解析带透明度的颜色
// 入参: value 色值, index 调色板索引, space 颜色空间标识, alpha 透明度
// 返回: color.Color 颜色对象
func (r *Renderer) parseColorWithAlpha(value string, index *int, space string, alpha *int) color.Color {
	result, err := r.ResolveColor(value, index, space, alpha)
	if err != nil {
		r.renderError = err
	}
	return result
}

// colorComponents 读取颜色空间及归一化分量，保留源位深供渐变插值
// 入参: value 色值, index 调色板索引, space 颜色空间标识
// 返回: string 颜色模型, [4]float64 单位分量, error 颜色定义错误
func (r *Renderer) colorComponents(value string, index *int, space string) (string, [4]float64, error) {
	cs := r.colorDefinition(space)
	if cs == nil && (space != "" || r.Reader != nil && r.Reader.doc != nil && r.Reader.doc.CommonData.DefaultCS != 0) {
		if space == "" {
			space = strconv.Itoa(r.Reader.doc.CommonData.DefaultCS)
		}
		return "", [4]float64{}, fmt.Errorf("color space %q not found", space)
	}
	kind, bits, count := "RGB", 8, 3
	if cs != nil {
		kind = strings.ToUpper(cs.Type)
		switch cs.BitsPerComponent {
		case 0:
		case 1, 2, 4, 8, 16:
			bits = cs.BitsPerComponent
		default:
			return "", [4]float64{}, fmt.Errorf("unsupported color depth %d", cs.BitsPerComponent)
		}
	}
	if strings.TrimSpace(value) == "" && index != nil {
		if cs == nil || *index < 0 || *index >= len(cs.Palette) {
			return "", [4]float64{}, fmt.Errorf("color palette index out of range")
		}
		value = cs.Palette[*index]
	}
	switch kind {
	case "RGB":
	case "GRAY":
		count = 1
	case "CMYK":
		count = 4
	default:
		return "", [4]float64{}, fmt.Errorf("unsupported color space %q", kind)
	}
	parts := strings.Fields(value)
	var components [4]float64
	limit := 1<<bits - 1
	if len(parts) != 0 && len(parts) != count {
		return "", components, fmt.Errorf("expected %d color components", count)
	}
	for i, part := range parts {
		v, err := parseColorComponent(part)
		if err != nil || v < 0 || limit < v {
			return "", [4]float64{}, fmt.Errorf("invalid color component %q", part)
		}
		components[i] = float64(v) / float64(limit)
	}
	return kind, components, nil
}

// parseColorComponent 解析颜色分量
// 入参: s 颜色分量
// 返回: int 颜色分量值, error 错误信息
func parseColorComponent(s string) (int, error) {
	if strings.HasPrefix(s, "#") {
		v, err := strconv.ParseInt(s[1:], 16, 0)
		return int(v), err
	}
	return strconv.Atoi(s)
}

// clampColor 限制颜色分量范围
// 入参: v 颜色分量
// 返回: int 颜色分量
func clampColor(v int) int {
	if v < 0 {
		return 0
	}
	if v > 255 {
		return 255
	}
	return v
}

// mergeAlpha 合并透明度
// 入参: colorAlpha 颜色透明度, objectAlpha 对象透明度
// 返回: *int 合并后的透明度
func mergeAlpha(colorAlpha, objectAlpha *int) *int {
	if colorAlpha == nil && objectAlpha == nil {
		return nil
	}
	for _, value := range []*int{colorAlpha, objectAlpha} {
		if value != nil && (*value < 0 || *value > 255) {
			alpha := *value
			return &alpha
		}
	}
	alpha := 255
	if colorAlpha != nil {
		alpha = *colorAlpha
	}
	if objectAlpha != nil {
		alpha = alpha * *objectAlpha / 255
	}
	return &alpha
}

// withFillAlpha 合并填充色透明度
// 入参: fillColor 填充颜色节点, alpha 对象透明度
// 返回: *FillColor 合并后的填充颜色节点
func withFillAlpha(fillColor *FillColor, alpha *int) *FillColor {
	if fillColor == nil || alpha == nil {
		return fillColor
	}
	merged := *fillColor
	merged.Alpha = mergeAlpha(fillColor.Alpha, alpha)
	return &merged
}

// withStrokeAlpha 合并勾边色透明度
// 入参: strokeColor 勾边颜色节点, alpha 对象透明度
// 返回: *StrokeColor 合并后的勾边颜色节点
func withStrokeAlpha(strokeColor *StrokeColor, alpha *int) *StrokeColor {
	if strokeColor == nil || alpha == nil {
		return strokeColor
	}
	merged := *strokeColor
	merged.Alpha = mergeAlpha(strokeColor.Alpha, alpha)
	return &merged
}

// colorWithAlpha 合并颜色透明度
// 入参: c 颜色对象, alpha 对象透明度
// 返回: color.Color 合并后的颜色对象
func colorWithAlpha(c color.Color, alpha *int) color.Color {
	if c == nil || alpha == nil {
		return c
	}
	a := clampColor(*alpha)
	rgba := colorToRGBA(c)
	return color.RGBA{
		R: uint8(int(rgba.R) * a / 255),
		G: uint8(int(rgba.G) * a / 255),
		B: uint8(int(rgba.B) * a / 255),
		A: uint8(int(rgba.A) * a / 255),
	}
}

// parseFillColor 解析填充颜色
// 入参: fillColor 填充颜色节点
// 返回: color.Color 颜色对象
func (r *Renderer) parseFillColor(fillColor *FillColor) color.Color {
	if fillColor == nil {
		return nil
	}
	if fillColor.Pattern != nil || fillColor.GouraudShd != nil || fillColor.LaGouraudShd != nil {
		return nil
	}
	if fillColor.AxialShd != nil {
		return r.parseShdColor(fillColor.AxialShd.Segment, fillColor.Alpha)
	}
	if fillColor.RadialShd != nil {
		return r.parseShdColor(fillColor.RadialShd.Segment, fillColor.Alpha)
	}
	if fillColor.unsupported && strings.TrimSpace(fillColor.Value) == "" && fillColor.Index == nil {
		return nil
	}
	return r.parseColorWithAlpha(fillColor.Value, fillColor.Index, fillColor.ColorSpace, fillColor.Alpha)
}

// parseStrokeColor 解析勾边颜色
// 入参: strokeColor 勾边颜色节点
// 返回: color.Color 颜色对象
func (r *Renderer) parseStrokeColor(strokeColor *StrokeColor) color.Color {
	return r.parseFillColor((*FillColor)(strokeColor))
}

// parsePatternPaint 解析底纹画刷
// 入参: fill 填充颜色节点
// 返回: *PatternPaint 底纹画刷
func parsePatternPaint(fill *FillColor) *PatternPaint {
	if fill.Pattern == nil {
		return nil
	}
	return &PatternPaint{Pattern: fill.Pattern, Color: FillColor{Value: fill.Value, Index: fill.Index, ColorSpace: fill.ColorSpace}, Alpha: fill.Alpha}
}

// parseShdColor 解析渐变颜色
// 入参: segments 渐变分段, alpha 透明度
// 返回: color.Color 颜色对象
func (r *Renderer) parseShdColor(segments []ShdSegment, alpha *int) color.Color {
	if len(segments) == 0 {
		return color.Black
	}
	c := segments[0].Color
	return r.parseColorWithAlpha(c.Value, c.Index, c.ColorSpace, mergeAlpha(c.Alpha, alpha))
}

// renderGradientStops 在源CMYK空间插值，保留截断边界及透明度变化
// 入参: segments 原始颜色分段, alpha 对象透明度
// 返回: []ColorStop 仅供绘制的颜色节点，不改变原始分段
func (r *Renderer) renderGradientStops(segments []ShdSegment, alpha *int) []ColorStop {
	stops, err := r.GradientStops(segments, alpha)
	if err != nil {
		r.renderError = err
		return nil
	}
	if len(stops) < 2 {
		return stops
	}
	var result []ColorStop
	for i, stop := range stops {
		if i > 0 && stops[i-1].Offset < stop.Offset {
			a, b := segments[i-1].Color, segments[i].Color
			leftKind, left, _ := r.colorComponents(a.Value, a.Index, a.ColorSpace)
			rightKind, right, _ := r.colorComponents(b.Value, b.Index, b.ColorSpace)
			leftSpace, rightSpace := r.colorDefinition(a.ColorSpace), r.colorDefinition(b.ColorSpace)
			if leftKind == "CMYK" && rightKind == "CMYK" && (leftSpace == nil || leftSpace.Profile == "") && (rightSpace == nil || rightSpace.Profile == "") {
				if result == nil {
					result = append([]ColorStop(nil), stops[:i]...)
				}
				result = append(result, cmykGradientStops(left, right, stops[i-1], stop)...)
			}
		}
		if result != nil {
			result = append(result, stop)
		}
	}
	if result == nil {
		return stops
	}
	return result
}

// cmykGradientStops 在加黑截断点分段，将预乘插值误差控制在四分之一灰阶内
// 入参: left 左端分量, right 右端分量, start 左端色标, end 右端色标
// 返回: []ColorStop 不含端点的显示色标
func cmykGradientStops(left, right [4]float64, start, end ColorStop) []ColorStop {
	positions := []float64{0, 1}
	a0, a1 := float64(start.Color.A)/255, float64(end.Color.A)/255
	bound := 0.0
	for channel := 0; channel < 3; channel++ {
		first, last := left[channel]+left[3], right[channel]+right[3]
		delta := last - first
		bound = math.Max(bound, 2*math.Abs((a1-a0)*delta))
		if delta != 0 {
			position := (1 - first) / delta
			if 0 < position && position < 1 {
				positions = append(positions, position)
			}
		}
	}
	slices.Sort(positions)
	positions = slices.Compact(positions)
	var result []ColorStop
	for i := 1; i < len(positions); i++ {
		first, last := positions[i-1], positions[i]
		steps := max(1, int(math.Ceil((last-first)*math.Sqrt(bound*255/2))))
		for step := 1; step <= steps; step++ {
			t := first + (last-first)*float64(step)/float64(steps)
			if t >= 1 {
				continue
			}
			var values [4]float64
			for channel := range values {
				values[channel] = left[channel]*(1-t) + right[channel]*t
			}
			r, g, b := meshRGB("CMYK", values)
			result = append(result, ColorStop{
				Offset: start.Offset*(1-t) + end.Offset*t,
				Color:  profileColor([3]float64{r, g, b}, a0*(1-t)+a1*t),
			})
		}
	}
	return result
}

// gradientPositions 按显式锚点补全渐变分段位置，保留原顺序
// 入参: segments 渐变分段
// 返回: []float64 分段位置
func gradientPositions(segments []ShdSegment) []float64 {
	positions := make([]float64, len(segments))
	position, step := 0.0, 0.0
	for i, segment := range segments {
		if !segment.positionMissing {
			position = segment.Position
		} else if i == len(segments)-1 {
			position = 1
		}
		if i == 0 || !segment.positionMissing {
			next := i + 1
			for next < len(segments)-1 && segments[next].positionMissing {
				next++
			}
			end := 1.0
			if next < len(segments) && !segments[next].positionMissing {
				end = segments[next].Position
			}
			step = (end - position) / float64(next-i)
		}
		positions[i] = position
		position += step
	}
	return positions
}

// colorToRGBA 转换颜色对象
// 入参: c 颜色对象
// 返回: color.RGBA RGBA颜色
func colorToRGBA(c color.Color) color.RGBA {
	if rgba, ok := c.(color.RGBA); ok {
		return rgba
	}
	r, g, b, a := c.RGBA()
	return color.RGBA{R: uint8(r >> 8), G: uint8(g >> 8), B: uint8(b >> 8), A: uint8(a >> 8)}
}