如何避免带有圆角的可缩放UserControl的彩色边框的视觉瑕疵？

Question

我有一个Form，其中包含：

1. a TrackBar（最小值= 1，最大值= 200，表示缩放百分比）;
2. 与UserControl的BorderStyle = BorderStyle.None。

Relevant code

Form1中

From designer code

trackBar1.Value = 100;
BackColor = Color.Gray;

From code-behind

private void trackBar1_Scroll(object sender, EventArgs e)
{
    userControl11.SetZoomFactor(trackBar1.Value / 100F);
}

的UserControl1

internal float MyBaseWidth;

public UserControl1()
{
    InitializeComponent();

    MyBaseWidth = Width;

    SetZoomFactor(1);
}

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);

    e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
    e.Graphics.CompositingQuality = CompositingQuality.HighQuality;
    e.Graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;

    Pen p = new Pen(Color.Yellow);
    e.Graphics.DrawPath(p, GraphicsPathWithBorder);
}

internal GraphicsPath GraphicsPathWithBorder;

internal void SetZoomFactor(float z)
{
    Width = (int)(MyBaseWidth * z);

    GraphicsPathWithBorder = RoundedCornerRectangle(ClientRectangle);
    Region = new Region(GraphicsPathWithBorder);
}

internal static GraphicsPath RoundedCornerRectangle(Rectangle r)
{
    GraphicsPath path = new GraphicsPath();
    float size = 10 * 2F;

    path.StartFigure();

    path.AddArc(r.X, r.Y,
        size, size, 180, 90);
    path.AddArc((r.X + (r.Width - size)), r.Y,
        size, size, 270, 90);
    path.AddArc((r.X + (r.Width - size)), (r.Y + (r.Height - size)),
        size, size, 0, 90);
    path.AddArc(r.X, (r.Y + (r.Height - size)),
        size, size, 90, 90);

    path.CloseFigure();

    return path;
}

Initial screenshot

Screenshot after using the trackbar

缩小后，黄色边框的右侧变为不可见，当放大时，右侧有多个黄色边框。

更新：

答案是可行的，但是有一部分控制超出了边界。 curveSize = 20右上角的屏幕截图：

并为curveSize = 24：

Answer 1

我建议使用稍微不同的方法来绘制边框和用户控件的内容，这也应该可以修复重绘控件时生成的工件。

为控件创建区域然后按原样绘制区域时，绘画的外边框不会消除锯齿：别名像素落在区域之外。当边界被绘制在区域的边界周围时，当然会产生相同的效果。

在这里，我应用了一个Scale Matrix和一个Translate Matrix，它在外部Region的内部缩放和移动Region的边界，定义了控件的边界。 缩放的大小和平移变换由笔大小决定。 关于Matrix用法的更多信息：Flip the GraphicsPath

在这种情况下，当边框被绘制时，边框的外部抗锯齿部分位于区域边界内，并且保留了抗锯齿。 Control的背景颜色设置为Color.Transparent（用户控件自身支持颜色透明度）。

我还添加了一些（非装饰的）属性，允许定义内部颜色（Control的BackgroundColor）和边框的大小和颜色。其余的或多或少都是以前的样子。

样品结果：

---

using System.Drawing;
using System.Drawing.Drawing2D;

public partial class RoundControl : UserControl
{
    private GraphicsPath GraphicsPathWithBorder;
    private float MyBaseWidth;
    private float m_PenSize = 2f;
    private Color m_BorderColor = Color.Yellow;
    private Color m_FillColor = Color.Green;

    public RoundControl()
    {
        this.ResizeRedraw = true;
        InitializeComponent();
        MyBaseWidth = Width;
    }

    public float BorderSize
    {
        get => this.m_PenSize;
        set {
            this.m_PenSize = value;
            this.Invalidate();
        }
    }

    public Color BorderColor
    {
        get => this.m_BorderColor;
        set {
            this.m_BorderColor = value;
            this.Invalidate();
        }
    }

    public Color FillColor
    {
        get => this.m_FillColor;
        set {
            this.m_FillColor = value;
            this.Invalidate();
        }
    }

    protected override void OnLayout(LayoutEventArgs e) {
        this.UpdateRegion();
        base.OnLayout(e);
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
        RectangleF rect = GraphicsPathWithBorder.GetBounds();
        float scaleX = 1 - ((m_PenSize + 1) / rect.Width);
        float scaleY = 1 - ((m_PenSize + 1) / rect.Height);
        using (Pen pen = new Pen(m_BorderColor, m_PenSize))
        using (Brush brush = new SolidBrush(m_FillColor))
        using (Matrix mx = new Matrix(scaleX, 0, 0, scaleY, pen.Width / 2, pen.Width / 2))
        {
            e.Graphics.Transform = mx;
            e.Graphics.FillPath(brush, GraphicsPathWithBorder);
            e.Graphics.DrawPath(pen, GraphicsPathWithBorder);
        }
    }

    private void UpdateRegion() {
        GraphicsPathWithBorder = RoundedCornerRectangle(ClientRectangle);
        Region = new Region(GraphicsPathWithBorder);
        this.Invalidate();
    }

    internal void SetZoomFactor(float z) {
        int newWidth = (int)(MyBaseWidth * z);
        if (newWidth <= (30 + this.m_PenSize * 2)) return;
        this.Width = newWidth;
        this.UpdateRegion();
    }

    private GraphicsPath RoundedCornerRectangle(Rectangle r)
    {
        GraphicsPath path = new GraphicsPath();
        float curveSize = 10 * 2.4F;

        path.StartFigure();
        path.AddArc(r.X, r.Y, curveSize, curveSize, 180, 90);
        path.AddArc(r.Right - curveSize, r.Y, curveSize, curveSize, 270, 90);
        path.AddArc(r.Right - curveSize, r.Bottom - curveSize, curveSize, curveSize, 0, 90);
        path.AddArc(r.X, r.Bottom - curveSize, curveSize, curveSize, 90, 90);
        path.CloseFigure();
        return path;
    }
}