c# - 如何避免带有圆角的可缩放用户控件的彩色边框的视觉伪影？

Question

我有一个 Form，其中包含:

1. 一个TrackBar(最小=1，最大=200，代表缩放百分比)；
2. UserControl 与 BorderStyle = BorderStyle.None。

相关代码

表格1

来自设计器代码

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

来自代码隐藏

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

用户控件1

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;
}

初始截图

使用轨迹栏后的截图

右边黄色边框缩小后不可见，放大时右边有多个黄色边框。

更新:

答案有效，但有一部分控件超出了边界。 curveSize = 20 右上角的屏幕截图:

对于 curveSize = 24:

Answer 1

我建议使用一种稍微不同的方法来绘制边框和用户控件的内容，该方法还应该解决重绘控件时生成的伪像。

当您为控件创建一个区域，然后按原样绘制该区域时，绘制的外边界未消除锯齿:锯齿像素落在该区域之外。当在区域边界周围绘制边框时，当然会应用相同的效果。

在这里，我申请了一个 Scale Matrix和一个 Translate Matrix 缩放和移动定义控件边界的外部区域内部的区域边界。
缩放和平移变换的大小由 Pen 大小决定。
有关 Matrix 用法的更多信息，请参见:Flip the GraphicsPath

在这种情况下，绘制边框时，边框的外部抗锯齿部分位于区域边界内，抗锯齿效果得以保留。
控件的背景颜色设置为 Color.Transparent(用户控件本身支持颜色透明度)。

我还添加了几个(非修饰的)属性，允许定义内部颜色(控件的 BackColor)以及边框的大小和颜色。其余部分与之前大致相同。

示例结果:

---

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()
    {
        ResizeRedraw = true;
        InitializeComponent();
        MyBaseWidth = Width;
    }

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

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

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

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

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

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


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

    private GraphicsPath RoundedCornerRectangle(Rectangle r)
    {
        GraphicsPath path = new GraphicsPath();
        // Fixed curve size since we only scale on X-dimension
        // Otherwise, adjust also considering the height
        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;
    }
}