SkiaSharp draw reversible shapes

Question

Is there a way to draw reversible shapes with SkiaSharp?

With reversible I mean outColor = srcColor XOR dstColor, so when you draw over same color again, the original color is restored. Like in WinForms ControlPaint.DrawReversibleFrame or (old) Windows FocusRects.

I'm using SkiaSharp 2.88.0

Answer 1

You can use Exclusion blend mode when drawing, for example:

// draw some random image on canvas
var bitmap = SKBitmap.Decode(@"random.jpg");
var info = new SKImageInfo(256, 256);
using var surf = SKSurface.Create(info);
var canvas = surf.Canvas;
canvas.DrawBitmap(bitmap, info.Rect);

// initialize paint with Exclusion blend mode
var paint = new SKPaint {
    Color = SKColors.Yellow,
    Style = SKPaintStyle.Fill,
    BlendMode = SKBlendMode.Exclusion
};

// draw overlapping rectangles using the paint
canvas.DrawRect(10, 10, 50, 50, paint);
canvas.DrawRect(25, 25, 50, 50, paint);

Result image: