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Do not stretch the background #2922

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merged 3 commits into from
Jul 5, 2024
+48 −20
Merged

Do not stretch the background #2922

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2985de8
Do not stretch the background
mattleibow Jul 4, 2024
53c51b5
Update SKXamlCanvas.cs
mattleibow Jul 4, 2024
2bb4eac
Scale the brush instead of stretching it
mattleibow Jul 4, 2024
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68 changes: 48 additions & 20 deletions source/SkiaSharp.Views/SkiaSharp.Views.WinUI/SKXamlCanvas.cs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
using System;
using Windows.ApplicationModel;
using Windows.Graphics.Display;

#if WINDOWS
using Microsoft.UI.Dispatching;
Expand Down Expand Up @@ -39,6 +38,7 @@ public partial class SKXamlCanvas : Canvas

private IntPtr pixels;
private WriteableBitmap bitmap;
private ImageBrush brush;
private bool ignorePixelScaling;
private bool isVisible = true;

Expand Down Expand Up @@ -101,8 +101,13 @@ private static void OnVisibilityChanged(DependencyObject d, DependencyPropertyCh
private void OnXamlRootChanged(XamlRoot xamlRoot = null, XamlRootChangedEventArgs e = null)
{
var root = xamlRoot ?? XamlRoot;
Dpi = root?.RasterizationScale ?? 1.0;
Invalidate();
var newDpi = root?.RasterizationScale ?? 1.0;
if (newDpi != Dpi)
Comment on lines +104 to +105
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This check here prevents hundreds of invalidations. The XamlRootChanged event will fire when any of the properties of the XAML root changes. This does not seem to fire just when the current view gets a new XAML root as the name implies.

{
Dpi = newDpi;
UpdateBrushScale();
Invalidate();
}
}
#else
private void OnDpiChanged(DisplayInformation sender, object args = null)
Expand Down Expand Up @@ -141,7 +146,7 @@ private void OnUnloaded(object sender, RoutedEventArgs e)
return;

#if WINDOWS
if(XamlRoot != null)
if (XamlRoot != null)
{
XamlRoot.Changed -= OnXamlRootChanged;
}
Expand Down Expand Up @@ -170,20 +175,26 @@ private void DoInvalidate()
if (!isVisible)
return;

var info = CreateBitmap(out var unscaledSize, out var dpi);
var (info, viewSize, dpi) = CreateBitmap();

if (info.Width <= 0 || info.Height <= 0)
{
CanvasSize = SKSize.Empty;
return;
}

var userVisibleSize = IgnorePixelScaling ? unscaledSize : info.Size;
// This is here because the property name is confusing and backwards.
// True actually means to ignore the pixel scaling of the raw pixel
// size and instead use the view size such that sizes match the XAML
// elements.
var matchUI = IgnorePixelScaling;

var userVisibleSize = matchUI ? viewSize : info.Size;
CanvasSize = userVisibleSize;

using (var surface = SKSurface.Create(info, pixels, info.RowBytes))
{
if (IgnorePixelScaling)
if (matchUI)
{
var canvas = surface.Canvas;
canvas.Scale(dpi);
Expand All @@ -195,30 +206,30 @@ private void DoInvalidate()
bitmap.Invalidate();
}

private SKSizeI CreateSize(out SKSizeI unscaledSize, out float dpi)
private (SKSizeI ViewSize, SKSizeI PixelSize, float Dpi) CreateSize()
{
unscaledSize = SKSizeI.Empty;
dpi = (float)Dpi;

var w = ActualWidth;
var h = ActualHeight;

if (!IsPositive(w) || !IsPositive(h))
return SKSizeI.Empty;
return (SKSizeI.Empty, SKSizeI.Empty, 1);

unscaledSize = new SKSizeI((int)w, (int)h);
return new SKSizeI((int)(w * dpi), (int)(h * dpi));
var dpi = (float)Dpi;
var viewSize = new SKSizeI((int)w, (int)h);
var pixelSize = new SKSizeI((int)(w * dpi), (int)(h * dpi));

return (viewSize, pixelSize, dpi);

static bool IsPositive(double value)
{
return !double.IsNaN(value) && !double.IsInfinity(value) && value > 0;
}
}

private SKImageInfo CreateBitmap(out SKSizeI unscaledSize, out float dpi)
private (SKImageInfo Info, SKSizeI PixelSize, float Dpi) CreateBitmap()
{
var size = CreateSize(out unscaledSize, out dpi);
var info = new SKImageInfo(size.Width, size.Height, SKImageInfo.PlatformColorType, SKAlphaType.Premul);
var (viewSize, pixelSize, dpi) = CreateSize();
var info = new SKImageInfo(pixelSize.Width, pixelSize.Height, SKImageInfo.PlatformColorType, SKAlphaType.Premul);

if (bitmap?.PixelWidth != info.Width || bitmap?.PixelHeight != info.Height)
FreeBitmap();
Expand All @@ -228,22 +239,39 @@ private SKImageInfo CreateBitmap(out SKSizeI unscaledSize, out float dpi)
bitmap = new WriteableBitmap(info.Width, info.Height);
pixels = bitmap.GetPixels();

var brush = new ImageBrush
brush = new ImageBrush
{
ImageSource = bitmap,
AlignmentX = AlignmentX.Left,
AlignmentY = AlignmentY.Top,
Stretch = Stretch.Fill
Stretch = Stretch.None
};
UpdateBrushScale();

Background = brush;
}

return info;
return (info, viewSize, dpi);
}

private void UpdateBrushScale()
{
if (brush == null)
return;

var scale = 1.0 / Dpi;

brush.Transform = new ScaleTransform
{
ScaleX = scale,
ScaleY = scale
};
}

private void FreeBitmap()
{
Background = null;
brush = null;
bitmap = null;
pixels = IntPtr.Zero;
}
Expand Down
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