ColorMatrix Invert black/white

[tinohager]

I try to draw an image and after the first drawing i want invert the color of the drawing.
If the background of my new square is black i need white and if it white i need black.
In my example i draw 3 squares and make a offset of 10 pixel in the x.

Unfortunately, it does not produce the wanted result.

using var skBitmap = new SKBitmap(100, 40);
using var skCanvas = new SKCanvas(skBitmap);
skCanvas.Clear(SKColors.White);

var color = SKColors.Black;
float[] invertMatrix = {
    -1.0f,  0.0f,  0.0f,  0.0f,  255.0f,
    0.0f,  -1.0f,  0.0f,  0.0f,  255.0f,
    0.0f,  0.0f,  -1.0f,  0.0f,  255.0f,
    0.0f,  0.0f,  0.0f,  1.0f,  0.0f
};

using var skPaint = new SKPaint();
skPaint.Color = color;
skPaint.Style = SKPaintStyle.Fill;

skCanvas.DrawRect(10, 10, 20, 20, skPaint);

skPaint.ColorFilter = SKColorFilter.CreateColorMatrix(invertMatrix);

//move +10 in x
skCanvas.DrawRect(20, 10, 20, 20, skPaint);

//move +10 in x
skCanvas.DrawRect(30, 10, 20, 20, skPaint);

[antoniohlopes]

You should check the SkiaSharpDemos

        public GrayScaleMatrixPage()
        {
            Title = "Gray-Scale Matrix";

            SKCanvasView canvasView = new SKCanvasView();
            canvasView.PaintSurface += OnCanvasViewPaintSurface;
            Content = canvasView;
        }

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

            canvas.Clear();

            using (SKPaint paint = new SKPaint())
            {
                paint.ColorFilter =
                    SKColorFilter.CreateColorMatrix(new float[]
                    {
                        0.21f, 0.72f, 0.07f, 0, 0,
                        0.21f, 0.72f, 0.07f, 0, 0,
                        0.21f, 0.72f, 0.07f, 0, 0,
                        0,     0,     0,     1, 0
                    });

                canvas.DrawBitmap(bitmap, info.Rect, BitmapStretch.Uniform, paint: paint);
            }
        }