feat(渲染能力): 完善径向渐变延伸与镜像渐变渲染，保持全矢量输出

ofdgo_shading.go

@@ -0,0 +1,195 @@
+// 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 (
+	"math"
+	"strconv"
+
+	"github.com/tdewolff/canvas"
+)
+
+type shdPaint struct {
+	gradient canvas.Gradient
+	extend   int
+	mapType  string
+	period   float64
+}
+
+// newShdPaint 创建渐变画刷
+// 入参: gradient 渐变对象, extend 延伸方向, mapType 绘制方式, mapUnit 渐变区间长度
+// 返回: *shdPaint 渐变画刷
+func newShdPaint(gradient canvas.Gradient, extend, mapType string, mapUnit float64) *shdPaint {
+	flags, _ := strconv.Atoi(extend)
+	length := 0.0
+	switch g := gradient.(type) {
+	case *canvas.LinearGradient:
+		length = g.End.Sub(g.Start).Length()
+	case *canvas.RadialGradient:
+		length = g.C1.Sub(g.C0).Length()
+	}
+	period := 1.0
+	if mapUnit > 0 && length > 0 {
+		period = mapUnit / length
+	}
+	return &shdPaint{gradient: gradient, extend: flags, mapType: mapType, period: period}
+}
+
+// resolveShdPaint 解析渐变画刷和裁剪区域
+// 入参: ctx 画布上下文, paint 画刷
+// 返回: any 画刷, *canvas.Path 裁剪区域
+func resolveShdPaint(ctx *canvas.Context, paint any) (any, *canvas.Path) {
+	s, ok := paint.(*shdPaint)
+	if !ok {
+		return paint, nil
+	}
+	switch g := s.gradient.(type) {
+	case *canvas.LinearGradient:
+		clip := axialShdClip(ctx, g, s.extend)
+		if s.mapType != "Reflect" {
+			return g, clip
+		}
+		d := g.End.Sub(g.Start)
+		axis := canvas.Matrix{{d.X, -d.Y, g.Start.X}, {d.Y, d.X, g.Start.Y}}
+		area := shdCanvasBounds(ctx).Transform(axis.Inv())
+		lo, hi := s.rangeLimits(area.X0, area.X1)
+		if hi <= lo {
+			return g, &canvas.Path{}
+		}
+		gradient := reflectShdGrad(g.Grad, s.period, lo, hi)
+		return gradient.ToLinear(g.Start.Add(d.Mul(lo)), g.Start.Add(d.Mul(hi))), clip
+	case *canvas.RadialGradient:
+		d, dr := g.C1.Sub(g.C0), g.R1-g.R0
+		length := d.Length()
+		if length >= math.Abs(dr) {
+			return g, nil
+		}
+		clip := radialShdClip(ctx, g, s.extend)
+		if s.mapType != "Reflect" {
+			return g, clip
+		}
+		lo, hi := 0.0, 1.0
+		if s.extend != 0 {
+			distance := 0.0
+			bounds := shdCanvasBounds(ctx)
+			for _, point := range []canvas.Point{{X: bounds.X0, Y: bounds.Y0}, {X: bounds.X1, Y: bounds.Y0}, {X: bounds.X1, Y: bounds.Y1}, {X: bounds.X0, Y: bounds.Y1}} {
+				distance = math.Max(distance, point.Sub(g.C0).Length())
+			}
+			limit := (distance + g.R0) / (math.Abs(dr) - length)
+			lo, hi = s.rangeLimits(-limit, limit)
+		}
+		if dr > 0 {
+			lo = math.Max(lo, -g.R0/dr)
+		} else {
+			hi = math.Min(hi, -g.R0/dr)
+		}
+		if hi <= lo {
+			return g, &canvas.Path{}
+		}
+		gradient := reflectShdGrad(g.Grad, s.period, lo, hi)
+		return gradient.ToRadial(g.C0.Add(d.Mul(lo)), math.Max(0, g.R0+dr*lo), g.C0.Add(d.Mul(hi)), math.Max(0, g.R0+dr*hi)), clip
+	}
+	return s.gradient, nil
+}
+
+// rangeLimits 限制渐变延伸区间
+// 入参: lo 区间起点, hi 区间终点
+// 返回: float64 起点, float64 终点
+func (s *shdPaint) rangeLimits(lo, hi float64) (float64, float64) {
+	if s.extend&1 == 0 {
+		lo = math.Max(lo, 0)
+	}
+	if s.extend&2 == 0 {
+		hi = math.Min(hi, 1)
+	}
+	return lo, hi
+}
+
+// shdCanvasBounds 获取渐变坐标系下的画布边界
+// 入参: ctx 画布上下文
+// 返回: canvas.Rect 画布边界
+func shdCanvasBounds(ctx *canvas.Context) canvas.Rect {
+	origin := ctx.CoordView().Dot(canvas.Point{})
+	view := ctx.CoordSystemView().Mul(ctx.View()).Translate(origin.X, origin.Y)
+	if view.Det() == 0 {
+		return canvas.Rect{}
+	}
+	width, height := ctx.Size()
+	return (canvas.Rect{X1: width, Y1: height}).Transform(view.Inv())
+}
+
+// radialShdClip 获取包含双圆的径向渐变裁剪区域
+// 入参: ctx 画布上下文, g 径向渐变, extend 延伸方向
+// 返回: *canvas.Path 裁剪区域
+func radialShdClip(ctx *canvas.Context, g *canvas.RadialGradient, extend int) *canvas.Path {
+	inner, outer := g.C0, g.C1
+	r0, r1 := g.R0, g.R1
+	if r1 < r0 {
+		inner, outer, r0, r1 = outer, inner, r1, r0
+		extend = (extend&1)<<1 | (extend&2)>>1
+	}
+	if extend == 3 {
+		return nil
+	}
+	var clip *canvas.Path
+	if extend&2 == 0 {
+		clip = canvas.Circle(r1).Translate(outer.X, outer.Y)
+	} else {
+		clip = shdCanvasBounds(ctx).ToPath()
+	}
+	if extend&1 == 0 && r0 > 0 {
+		clip = clip.Not(canvas.Circle(r0).Translate(inner.X, inner.Y))
+	}
+	return clip
+}
+
+// reflectShdGrad 构造镜像渐变颜色分段
+// 入参: gradient 颜色分段, period 周期长度, lo 起点, hi 终点
+// 返回: canvas.Grad 镜像颜色分段
+func reflectShdGrad(gradient canvas.Grad, period, lo, hi float64) canvas.Grad {
+	base := append(canvas.Grad{{Offset: 0, Color: gradient.At(0)}}, gradient...)
+	base = append(base, canvas.Stop{Offset: 1, Color: gradient.At(1)})
+	reversed := make(canvas.Grad, len(base))
+	for i, stop := range base {
+		reversed[len(base)-1-i] = canvas.Stop{Offset: 1 - stop.Offset, Color: stop.Color}
+	}
+	result := canvas.Grad{{Offset: 0, Color: gradient.At(reflectShdPosition(lo / period))}}
+	for i, last := math.Floor(lo/period), math.Ceil(hi/period); i < last; i++ {
+		stops := base
+		if math.Mod(i, 2) != 0 {
+			stops = reversed
+		}
+		for _, stop := range stops {
+			position := (i + stop.Offset) * period
+			offset := (position - lo) / (hi - lo)
+			if lo < position && position < hi && result[len(result)-1].Offset < offset {
+				result = append(result, canvas.Stop{Offset: offset, Color: stop.Color})
+			}
+		}
+	}
+	return append(result, canvas.Stop{Offset: 1, Color: gradient.At(reflectShdPosition(hi / period))})
+}
+
+// reflectShdPosition 获取镜像周期内的位置
+// 入参: position 渐变位置
+// 返回: float64 周期内的位置
+func reflectShdPosition(position float64) float64 {
+	index := math.Floor(position)
+	position -= index
+	if math.Mod(index, 2) != 0 {
+		return 1 - position
+	}
+	return position
+}