Backend Development
C++
Why Do Rounded Corners on a Zoomed UserControl Exhibit Visual Artifacts, and How Can They Be Resolved?
Why Do Rounded Corners on a Zoomed UserControl Exhibit Visual Artifacts, and How Can They Be Resolved?
Jan 06, 2025 am 04:34 AM
Visual Artifacts While Zooming UserControl with Rounded Corners
Problem:
A UserControl with rounded corners and a colored border exhibits visual artifacts when zoomed. The border becomes invisible on one side during zooming out and multiple borders appear on the same side when zooming in.
Solution:
Instead of painting the Region directly, apply Scale and Translate transformations to move the painted area slightly inward within the control's Region. This ensures that the anti-aliased pixels of the border are within the Region, preserving the anti-aliasing effect.
Implementation:
- Set the User Control's BackgroundColor to Color.Transparent to support color transparency.
- Create GraphicsPathWithBorder and Region to define the control's shape.
-
In the OnPaint event:
- Set the SmoothingMode to AntiAlias.
- Calculate scale and translate values based on the Pen size.
- Apply the transformations using a Matrix.
- Fill and draw the path using a Brush and Pen, respectively.
- Handle zooming by updating the Width and recalculating the Region.
Example:
using System.Drawing;
using System.Drawing.Drawing2D;
public class RoundControl : UserControl
{
// ...
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);
}
// ...
}
Result:
This approach eliminates the visual artifacts and provides a seamless and visually appealing zooming effect.
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