How Can I Eliminate Visual Artifacts in Resizable, Zoomable UserControls with Rounded Corners?

Eliminating Visual Artifacts in Resizable Zoomable UserControls with Rounded Corners

In this issue, a UserControl with rounded corners and colored borders exhibits visual artifacts when zoomed in or out. The right side of the border becomes invisible when zoomed out, and multiple yellow borders appear on the right side when zoomed in.

Problem Explanation

The visual artifacts arise from the way the UserControl's Region is defined and the border is painted. When the Region is created, its outer borders are not anti-aliased, leading to the loss of the outer section of the painted border outside the Region.

Suggested Solution

To resolve this issue, a modified drawing approach is proposed:

1. Use Matrix Transformations: Apply scale and translate matrices to the Region bounds to move them inside the control's outer Region. This ensures that the anti-aliased section of the border is within the Region's bounds.
2. Update Painting Code: Utilize an updated OnPaint method that fills the Region with the background color and draws the border using appropriate pen size and color settings.
3. Define Borders and Background: Implement properties to define the BorderSize, BorderColor, and FillColor of the UserControl.
4. Handle Layout Changes: In the OnLayout event, update the Region to accommodate changes in size.

Code Sample

The following code demonstrates these modifications:

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

public class RoundedControl : UserControl
{
    // ... Your existing code

    // ... Added code suggested in the solution

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

Benefits of the Solution

• Eliminates the visual artifacts of the colored border.
• Maintains anti-aliasing effects around the border.
• Allows customization of border appearance.

Note: The curveSize in the RoundedCornerRectangle method may need to be adjusted to prevent parts of the control from extending beyond the border.

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