如何合并带Z序效果的自相交GraphicsPath为单个图形对象？

需要创建具有Z序视觉效果的带边框自相交图形：后绘制的路径覆盖前路径的重叠区域，且两个路径各自保留完整边框。当前分开绘制两个GraphicsPath可实现预期效果，但合并为单个路径后，填充和边框均不符合需求。

现有实现（分开绘制，效果正确） #

private void Example1(PaintEventArgs e) {
    Brush brush = new SolidBrush(Color.FromArgb(200, Color.LightBlue));

    GraphicsPath path1 = new GraphicsPath(FillMode.Winding);
    path1.AddLines(new Point[] {
        new Point(400, 200),
        new Point(400, 300),
        new Point(100, 300),
        new Point(100, 400),
        new Point(500, 400),
        new Point(500, 100)
    });
    e.Graphics.FillPath(brush, path1);
    e.Graphics.DrawPath(Pens.Blue, path1);

    GraphicsPath path2 = new GraphicsPath(FillMode.Winding);
    path2.AddLines(new Point[] {
        new Point(500, 100),
        new Point(200, 100),
        new Point(200, 500),
        new Point(300, 500),
        new Point(300, 200),
        new Point(400, 200)
    });
    e.Graphics.FillPath(brush, path2);
    e.Graphics.DrawPath(Pens.Blue, path2);
}

合并路径后的问题（效果不符合预期） #

合并路径后，系统会按FillMode规则计算整体填充区域，边框也会变成整个路径的外轮廓，丢失了两个路径的独立边框和Z序覆盖效果：

private void Example2(PaintEventArgs e) {
    Brush brush = new SolidBrush(Color.FromArgb(200, Color.LightBlue));

    GraphicsPath path1 = new GraphicsPath(FillMode.Winding);
    path1.AddLines(new Point[] {
        new Point(400, 200),
        new Point(400, 300),
        new Point(100, 300),
        new Point(100, 400),
        new Point(500, 400),
        new Point(500, 100)
    });

    GraphicsPath path2 = new GraphicsPath(FillMode.Winding);
    path2.AddLines(new Point[] {
        new Point(500, 100),
        new Point(200, 100),
        new Point(200, 500),
        new Point(300, 500),
        new Point(300, 200),
        new Point(400, 200)
    });

    path1.AddPath(path2, true);
    e.Graphics.FillPath(brush, path1);
    e.Graphics.DrawPath(Pens.Blue, path1);
}

简便解决方案：单个GraphicsPath+子路径遍历绘制 #

将两个路径作为独立子路径存入单个GraphicsPath，绘制时遍历每个子路径分别填充和描边，既保留单个对象的可操作性（统一变换），又还原分开绘制的视觉效果：

步骤1：封装遍历绘制方法 #

public static void DrawPathWithZOrder(Graphics g, Brush brush, Pen pen, GraphicsPath path)
{
    using (GraphicsPathIterator iterator = new GraphicsPathIterator(path))
    {
        using (GraphicsPath subPath = new GraphicsPath())
        {
            bool isClosed;
            while (iterator.NextSubpath(subPath, out isClosed))
            {
                g.FillPath(brush, subPath);
                g.DrawPath(pen, subPath);
                subPath.Reset();
            }
        }
    }
}

步骤2：创建包含子路径的单个GraphicsPath #

private void Example3(PaintEventArgs e)
{
    Brush brush = new SolidBrush(Color.FromArgb(200, Color.LightBlue));
    GraphicsPath combinedPath = new GraphicsPath(FillMode.Winding);

    // 添加第一个子路径
    combinedPath.StartFigure();
    combinedPath.AddLines(new Point[] {
        new Point(400, 200),
        new Point(400, 300),
        new Point(100, 300),
        new Point(100, 400),
        new Point(500, 400),
        new Point(500, 100)
    });
    combinedPath.CloseFigure();

    // 添加第二个子路径
    combinedPath.StartFigure();
    combinedPath.AddLines(new Point[] {
        new Point(500, 100),
        new Point(200, 100),
        new Point(200, 500),
        new Point(300, 500),
        new Point(300, 200),
        new Point(400, 200)
    });
    combinedPath.CloseFigure();

    // 统一变换示例（可选）
    e.Graphics.TranslateTransform(50, 50);

    // 使用自定义方法绘制，还原Z序和独立边框
    DrawPathWithZOrder(e.Graphics, brush, Pens.Blue, combinedPath);
}

原理说明 #

• StartFigure()和CloseFigure()将两条路径标记为GraphicsPath中的独立子路径
• GraphicsPathIterator负责遍历每个子路径，分别执行填充和描边，完全复刻分开绘制的视觉效果
• 单个combinedPath可直接应用平移、缩放等变换，满足“单个图形对象处理”的需求

内容的提问来源于stack exchange，提问作者stenio