[Bug] Concatenating an AffineTransform has no effect on Android

[davidbritch]

I've been using a MAUI GraphicsView to experiment with the AffineTransform class on Android. Long story short is whenever you concatenate your AffineTransform onto the canvas, then draw an object, you get a blank canvas.

Looking at the source code, it looks like the implementation is unfinished.

Take the following code that draws an 11-pointed star centred at (0,0):

            PathF path = new PathF();
            for (int i = 0; i < 11; i++)
            {
                double angle = 5 * i * 2 * Math.PI / 11;
                PointF point = new PointF(100 * (float)Math.Sin(angle), -100 * (float)Math.Cos(angle));
 
                if (i == 0)
                    path.MoveTo(point);
                else
                    path.LineTo(point);
            }
 
            canvas.FillColor = Colors.Red;
            canvas.Translate(150, 150);
            canvas.FillPath(path);

It has to be translated to fully appear on the screen. Trying the same with an AffineTransform yields a blank canvas:

            PathF path = new PathF();
            for (int i = 0; i < 11; i++)
            {
                double angle = 5 * i * 2 * Math.PI / 11;
                PointF point = new PointF(100 * (float)Math.Sin(angle), -100 * (float)Math.Cos(angle));
 
                if (i == 0)
                    path.MoveTo(point);
                else
                    path.LineTo(point);
            }
 
            canvas.FillColor = Colors.Red;
            AffineTransform transform = new AffineTransform();
            transform.SetToTranslation(150, 150);           
            canvas.ConcatenateTransform(transform);
            canvas.FillPath(path);