Introduction

When creating an Uno Platform application, developers might want to create elaborate 2D graphics using a library such as Skia or Cairo, rather than using, for example, a simple Canvas. To support this use case, SkiaSharp comes with an SKXamlCanvas element that allows for drawing in an area using SkiaSharp.

On Uno Platform targets with Skia rendering, we can utilize the pre-existing internal Skia canvas used to render the application window instead of creating additional Skia surfaces. Unlike SKXamlCanvas which doesn't support hardware acceleration on Skia targets yet, hardware acceleration comes out of the box if the Uno application is already using OpenGL to render. Moreover, SKXamlCanvas has to make additional buffer copying, which can be skipped with this implementation.

Important

. The Uno.WinUI.Graphics2DSK package which provides the SKCanvasElement class is referenced for you by Uno.Sdk automatically when the Skia or SkiaRenderer features are present, and is always referenced on the netX.0-desktop target. However, the class is only supported (i.e. SKCanvasElement.IsSupportedOnCurrentPlatform returns true) on the netX.0-desktop target and on other targets that use skia rendering, for example netX.0-android with the SkiaRenderer feature.

SKCanvasElement

SKCanvasElement is an abstract FrameworkElement for 2D drawing with Skia. To use SKCanvasElement, create a subclass of SKCanvasElement and override the RenderOverride method, which takes the canvas that will be drawn on and the clipping area inside the canvas.

protected abstract void RenderOverride(SKCanvas canvas, Size area);

When adding your drawing logic in RenderOverride on the provided canvas, you can assume that the origin is already translated so that 0,0 is the origin of the element, not the entire window. Drawing outside this area will be clipped.

Additionally, SKCanvasElement has an Invalidate method that invalidates the SKCanvasElement and triggers a redraw. The drawing of the SKCanvasElement is often cached and will not be updated unless Invalidate is called.

Since SKCanvasElement is just a FrameworkElement, controlling the dimensions of the drawing area is done by manipulating the layout of the element, e.g. by overriding MeasureOverride and ArrangeOverride.

Finally, since SKCanvasElement makes use of the Skia-based rendering infrastructure and is therefore only supported when skia rendering is used, there's a static method that provides a check at runtime for whether SKCanvasElement can function on the current platform.

public static bool IsSupportedOnCurrentPlatform();

Attempting to create an SKCanvasElement instance when IsSupportedOnCurrentPlatform returns false throws an exception.

Full example

For a complete example that showcases how to work with SKCanvasElement, see this sample in the Uno.Samples repository

WinAppSDK Specifics

When using the SKCanvasElement and running on WinAppSDK, make sure to create an x64 or ARM64 configuration:

• In the Visual Studio configuration manager, create an x64 or ARM64 solution configuration
• Assign it to the Uno Platform project
• Debug your application using the configuration relevant to your current environment