feat(编辑能力): 新增画笔和注解创建，完善水印、印章与链接编辑，优化选取和保存体验

ofdgo_ink.go

@@ -0,0 +1,101 @@
+// 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"
+
+	"github.com/tdewolff/canvas"
+)
+
+// InkPoint 手写采样点，X和Y为毫米，Pressure为0到1的压力
+type InkPoint struct {
+	X        float64 `json:"x"`
+	Y        float64 `json:"y"`
+	Pressure float64 `json:"pressure"`
+}
+
+// NewInk 将采样点转为标准矢量路径，等宽笔保留中心线，压感笔使用一次填充的连续轮廓
+// 不推测笔压、不修改输入；单点生成圆点，页面外路径由页面边界裁切
+// 入参: points 采样点, width 等宽线宽或压感最大线宽，单位毫米, pressure 是否使用压力
+// 返回: PathObject 黑色笔迹，可修改颜色和透明度后插入页面或注解, error 错误信息
+func NewInk(points []InkPoint, width float64, pressure bool) (PathObject, error) {
+	if len(points) == 0 || !finite(width) || width <= 0 {
+		return PathObject{}, fmt.Errorf("ink requires points and a positive finite width")
+	}
+	path := &canvas.Path{}
+	stationary := true
+	for i, point := range points {
+		if !finite(point.X) || !finite(point.Y) || !finite(point.Pressure) || point.Pressure < 0 || point.Pressure > 1 {
+			return PathObject{}, fmt.Errorf("invalid ink point %d", i)
+		}
+		stationary = stationary && point.X == points[0].X && point.Y == points[0].Y
+		if !pressure {
+			if i == 0 {
+				path.MoveTo(point.X, point.Y)
+			} else {
+				path.LineTo(point.X, point.Y)
+			}
+			continue
+		}
+		radius := width * point.Pressure / 2
+		if radius > 0 {
+			path = path.Append(canvas.Circle(radius).Translate(point.X, point.Y))
+		}
+		if i == 0 {
+			continue
+		}
+		previous := points[i-1]
+		r := width * previous.Pressure / 2
+		dx, dy := point.X-previous.X, point.Y-previous.Y
+		length := math.Hypot(dx, dy)
+		if radius == 0 && r == 0 || length <= math.Abs(radius-r) {
+			continue
+		}
+		x, y := dx/length, dy/length
+		a := (r - radius) / length
+		b := math.Sqrt(1 - a*a)
+		nx, ny, mx, my := a*x-b*y, a*y+b*x, a*x+b*y, a*y-b*x
+		segment := &canvas.Path{}
+		segment.MoveTo(previous.X+r*mx, previous.Y+r*my)
+		segment.LineTo(point.X+radius*mx, point.Y+radius*my)
+		segment.LineTo(point.X+radius*nx, point.Y+radius*ny)
+		segment.LineTo(previous.X+r*nx, previous.Y+r*ny)
+		segment.Close()
+		path = path.Append(segment)
+	}
+	filled := pressure || stationary
+	if !pressure && stationary {
+		path = canvas.Circle(width/2).Translate(points[0].X, points[0].Y)
+	}
+	if path.Empty() {
+		return PathObject{}, fmt.Errorf("ink has no visible stroke")
+	}
+	box := path.Bounds()
+	padding := width / 2
+	boundary := Box{X: box.X0 - padding, Y: box.Y0 - padding, W: math.Max(box.W(), width) + width, H: math.Max(box.H(), width) + width}
+	object := editorClipPath(path.Translate(-boundary.X, -boundary.Y))
+	object.Boundary = editorBoxString(boundary)
+	stroke := !filled
+	object.Fill, object.Stroke = &filled, &stroke
+	object.Cap, object.Join, object.LineWidth = "Round", "Round", width
+	if filled {
+		object.FillColor = &FillColor{Value: "0 0 0"}
+	} else {
+		object.StrokeColor = &StrokeColor{Value: "0 0 0"}
+	}
+	return object, nil
+}