Xamarin Forms and SkiaSharp, implementing moving cursor on bitmap

Question

I am writing a Xamarin Forms app that loads a bitmap from an embedded resource and uses it as background for a moving cursor. I use a typical event handler for painting the bitmap:

private void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args)
{
    SKImageInfo info = args.Info;
    SKSurface surface = args.Surface;
    SKCanvas canvas = surface.Canvas;

    canvas.Clear();
    canvas.DrawBitmap(bitmap, info.Rect, BitmapStretch.AspectFill);
}

The cursor is drawn using code like:

private void DrawOverlay()
{
    using (SKCanvas canvas = new SKCanvas(bitmap))
    {
        UserSprite.Draw(locationInPix, rotation, canvas); // static function

        view.InvalidateSurface(); // view is the corresponding SKCanvasView
    }
}

A timer reads the position (GPS) and rotation (compass) and calls the DrawOverlay function periodically. Question: how do I erase the previous cursor image when drawing a new one at a new position without trashing the background bitmap?

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

how do I erase the previous cursor image when drawing a new one at a new position without trashing the background bitmap

Do you mean saving the bitmap when clearing the drawing? We cannot do that. When calling the SKCanvas.Clear command to the redraw the canvas, the bitmap will be also cleared. SKCanvas doesn't provide a method to keep the bitmap.

Best Regards,

Jarvan Zhang

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