public void FastAlphaBlending()
{
// http://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending
// using premultiplied values
// out_a = a1 + a2 * (1 - a1)
// out_rgb = r1 + r2 * (1 - a1)
var c = new PixelArrayCanvas(0, 0);
var foreground = c.GetColor(System.Windows.Media.Colors.Green.ChangeAlpha(127));
var background = c.GetColor(System.Windows.Media.Colors.White.ChangeAlpha(127));
// get premultiplied components
var background_a = background >> 24 & 0xff;
var background_r = background >> 16 & 0xff;
var background_g = background >> 8 & 0xff;
var background_b = background & 0xff;
var foreground_a = foreground >> 24 & 0xff;
var foreground_r = foreground >> 16 & 0xff;
var foreground_g = foreground >> 8 & 0xff;
var foreground_b = foreground & 0xff;
var out_a = foreground_a + (1 - foreground_a) * background_a;
var out_r = foreground_r + (background_r) * (1 - foreground_a);// / out_a;
var out_g = foreground_g + (background_g) * (1 - foreground_a);// / out_a;
var out_b = foreground_b + (background_b) * (1 - foreground_a);// / out_a;
var pc = new PixelArrayCanvas(10, 10);
pc.DrawLineDDA(1, 1, 1, 8, foreground);
pc.DrawLineDDA(2, 1, 2, 8, background);
pc.DrawLineDDA(4, 1, 4, 2, PixelCanvas.GetColor((int)(out_a ),(int)(out_r ), (int)(out_g ),(int)(out_b )));
var pc3 = new PixelArrayCanvas(10,10);
pc3.DrawLineDDA(4,3,4,5, foreground);
pc.Blit(pc3, BlendMode.Alpha);
out_a = foreground_a + (1 - foreground_a) * background_a;
out_r = foreground_r + (background_r) * (1 - foreground_a) / out_a;
out_g = foreground_g + (background_g) * (1 - foreground_a) / out_a;
out_b = foreground_b + (background_b) * (1 - foreground_a) / out_a;
pc.DrawLineDDA(4, 6, 4, 8, PixelCanvas.GetColor((int)(out_a ), (int)(out_r ), (int)(out_g ), (int)(out_b )));
pc.Save(@"c:\temp\blend_xxx.bmp");
}
IPixelCanvas RandomSquares__RAW(int count, int square_size, int canvas_size)
{
var rd = new Random();
var pc = new PixelArrayCanvas(canvas_size, canvas_size);
var color = pc.GetColor(System.Windows.Media.Colors.Red);
Parallel.For(0, count, i =>
{
var x = rd.Next(0, canvas_size - square_size);
var y = rd.Next(0, canvas_size - square_size);
pc.DrawRectangle(
//pc.Bounds,
x,
y,
square_size,
square_size,
color);
});
return pc;
}