/// <summary>
/// Abstract class used to create WPF controls which are drawn using Skia
/// </summary>
[PublicAPI]
public abstract class SkiaControl : FrameworkElement
{
private WriteableBitmap _bitmap;
private SKColor _canvasClearColor;
protected SkiaControl()
{
cacheCanvasClearColor();
createBitmap();
SizeChanged += (o, args) => createBitmap();
}
/// <summary>
/// Color used to clear canvas before each call to <see cref="Draw" /> if <see cref="IsClearCanvas" /> is true
/// </summary>
[Category("Brush")]
[Description("Gets or sets a color used to clear canvas before each render if IsClearCanvas is true")]
public SolidColorBrush CanvasClear
{
get { return (SolidColorBrush)GetValue(CanvasClearProperty); }
set { SetValue(CanvasClearProperty, value); }
}
public static readonly DependencyProperty CanvasClearProperty =
DependencyProperty.Register("CanvasClear", typeof(SolidColorBrush), typeof(SkiaControl),
new PropertyMetadata(new SolidColorBrush(Colors.Transparent), canvasClearPropertyChanged));
private static void canvasClearPropertyChanged(DependencyObject o, DependencyPropertyChangedEventArgs args)
{
((SkiaControl)o).cacheCanvasClearColor();
}
/// <summary>
/// When enabled, canvas will be cleared before each call to <see cref="Draw" /> with the value of
/// <see cref="CanvasClear" />
/// </summary>
[Category("Appearance")]
[Description(
"Gets or sets a bool to determine if canvas should be cleared before each render with the value of CanvasClear")]
public bool IsClearCanvas
{
get { return (bool)GetValue(IsClearCanvasProperty); }
set { SetValue(IsClearCanvasProperty, value); }
}
public static readonly DependencyProperty IsClearCanvasProperty =
DependencyProperty.Register("IsClearCanvas", typeof(bool), typeof(SkiaControl), new PropertyMetadata(true));
/// <summary>
/// Capture the most recent control render to an image
/// </summary>
/// <returns>An <see cref="ImageSource"/> containing the captured area</returns>
[CanBeNull]
public BitmapSource SnapshotToBitmapSource() => _bitmap?.Clone();
protected override void OnRender(DrawingContext dc)
{
if (_bitmap == null)
return;
_bitmap.Lock();
using (var surface = SKSurface.Create((int)_bitmap.Width, (int)_bitmap.Height,
SKColorType.N_32, SKAlphaType.Premul, _bitmap.BackBuffer, _bitmap.BackBufferStride))
{
if (IsClearCanvas)
surface.Canvas.Clear(_canvasClearColor);
Draw(surface.Canvas, (int)_bitmap.Width, (int)_bitmap.Height);
}
_bitmap.AddDirtyRect(new Int32Rect(0, 0, (int)_bitmap.Width, (int)_bitmap.Height));
_bitmap.Unlock();
dc.DrawImage(_bitmap, new Rect(0, 0, ActualWidth, ActualHeight));
}
/// <summary>
/// Override this method to implement the drawing routine for the control
/// </summary>
/// <param name="canvas">The Skia canvas</param>
/// <param name="width">Canvas width</param>
/// <param name="height">Canvas height</param>
protected abstract void Draw(SKCanvas canvas, int width, int height);
private void createBitmap()
{
int width = (int)ActualWidth;
int height = (int)ActualHeight;
if (height > 0 && width > 0 && Parent != null)
_bitmap = new WriteableBitmap(width, height, 96, 96, PixelFormats.Pbgra32, null);
else
_bitmap = null;
}
private void cacheCanvasClearColor()
{
_canvasClearColor = CanvasClear.ToSkia();
}
}
