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Fix white border artifact on maximized Form (Windows 11) #116

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Fix white border artifact on maximized Form (Windows 11) #116

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Copilot Apr 3, 2026
8a63bc0
Fix white border artifact when maximizing Form on Windows 11
Copilot Apr 3, 2026
9b3dba8
Fix maximize white border: use framebuffer size in DoPaint and Math.C…
Copilot Apr 4, 2026
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16 changes: 16 additions & 0 deletions src/Modern.Forms/Form.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ public class Form : WindowBase, ICloseable
private bool show_focus_cues;
private string text = string.Empty;
private bool use_system_decorations;
private readonly ControlStyle maximized_style;

/// <summary>
/// Initializes a new instance of the Form class.
Expand All @@ -32,6 +33,11 @@ public Form () : base (AvaloniaGlobals.GetRequiredService<IWindowingPlatform> ()
{
TitleBar = Controls.AddImplicitControl (new FormTitleBar ());

// Style used when the window is maximized: inherits everything from the instance
// Style but suppresses the border so no thin colored strip is visible at the edges.
maximized_style = new ControlStyle (Style);
maximized_style.Border.Width = 0;

Resizeable = true;
Window.SetSystemDecorations (SystemDecorations.None);
Window.SetExtendClientAreaToDecorationsHint (true);
Expand Down Expand Up @@ -79,6 +85,10 @@ public bool AllowMinimize {
}
}

/// <inheritdoc/>
/// <remarks>Returns a no-border style when the window is maximized to prevent a thin border artifact at screen edges.</remarks>
public override ControlStyle CurrentStyle => WindowState == FormWindowState.Maximized ? maximized_style : base.CurrentStyle;

/// <inheritdoc/>
public override void Close ()
{
Expand Down Expand Up @@ -183,6 +193,9 @@ private WindowElement GetElementAtLocation (int x, int y)

internal override bool HandleMouseDown (int x, int y)
{
if (WindowState == FormWindowState.Maximized)
return false;

var element = GetElementAtLocation (x, y);

switch (element) {
Expand Down Expand Up @@ -217,6 +230,9 @@ internal override bool HandleMouseDown (int x, int y)

internal override bool HandleMouseMove (int x, int y)
{
if (WindowState == FormWindowState.Maximized)
return base.HandleMouseMove (x, y);

var element = GetElementAtLocation (x, y);

switch (element) {
Expand Down
23 changes: 18 additions & 5 deletions src/Modern.Forms/WindowBase.cs
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Expand Up @@ -294,17 +294,26 @@ private void DoPaint (Rect r)
var framebufferImageInfo = new SKImageInfo (framebuffer.Size.Width, framebuffer.Size.Height,
framebuffer.Format.ToSkColorType (), framebuffer.Format == PixelFormat.Rgb565 ? SKAlphaType.Opaque : SKAlphaType.Premul);

var scaled_client_size = ScaledClientSize;
var scaled_display_rect = ScaledDisplayRectangle;
// Use the actual framebuffer pixel dimensions directly. Computing the size via
// (int)(ClientSize * RenderScaling) can lose 1 pixel at fractional DPI (e.g. 150%)
// because the float round-trip (pixels / scale * scale) truncates to one fewer pixel,
// leaving a strip of unfilled background at the right/bottom edges.
var fb_width = framebuffer.Size.Width;
var fb_height = framebuffer.Size.Height;
var border = CurrentStyle.Border;
var fb_display_rect = new System.Drawing.Rectangle (
border.Left.GetWidth (), border.Top.GetWidth (),
fb_width - border.Left.GetWidth () - border.Right.GetWidth (),
fb_height - border.Top.GetWidth () - border.Bottom.GetWidth ());

using var surface = SKSurface.Create (framebufferImageInfo, framebuffer.Address, framebuffer.RowBytes);

var e = new PaintEventArgs (framebufferImageInfo, surface.Canvas, Scaling);
OnPaintBackground (e);
e.Canvas.DrawBorder (new System.Drawing.Rectangle (0, 0, (int)scaled_client_size.Width, (int)scaled_client_size.Height), CurrentStyle);
e.Canvas.DrawBorder (new System.Drawing.Rectangle (0, 0, fb_width, fb_height), CurrentStyle);
OnPaint (e);

e.Canvas.ClipRect (new SKRect (scaled_display_rect.Left, scaled_display_rect.Top, scaled_display_rect.Width + 1, scaled_display_rect.Height + 1));
e.Canvas.ClipRect (new SKRect (fb_display_rect.Left, fb_display_rect.Top, fb_display_rect.Right, fb_display_rect.Bottom));

adapter.RaisePaintBackground (e);
adapter.RaisePaint (e);
Expand Down Expand Up @@ -344,7 +353,11 @@ protected virtual void OnPaintBackground (PaintEventArgs e)

private void OnResize (Size size, WindowResizeReason reason)
{
adapter.SetBounds (DisplayRectangle.Left, DisplayRectangle.Top, Size.Width, Size.Height);
// Use Math.Ceiling so controls are sized to cover the full framebuffer even when
// the logical window size is fractional (e.g. 2576 device px / 1.5 = 1717.33 logical px).
// Without ceiling, (int) truncation would make controls 1 logical pixel too narrow,
// leaving a strip of form background showing at the right/bottom edges.
adapter.SetBounds (DisplayRectangle.Left, DisplayRectangle.Top, (int)Math.Ceiling (size.Width), (int)Math.Ceiling (size.Height));
}

/// <summary>
Expand Down