Draw Bitmap with alpha channel
- by Paja
I have a Format32bppArgb backbuffer, where I draw some lines:
var g = Graphics.FromImage(bitmap);
g.Clear(Color.FromArgb(0));
var rnd = new Random();
for (int i = 0; i < 5000; i++) {
int x1 = rnd.Next(ClientRectangle.Left, ClientRectangle.Right);
int y1 = rnd.Next(ClientRectangle.Top, ClientRectangle.Bottom);
int x2 = rnd.Next(ClientRectangle.Left, ClientRectangle.Right);
int y2 = rnd.Next(ClientRectangle.Top, ClientRectangle.Bottom);
Color color = Color.FromArgb(rnd.Next(0, 255), rnd.Next(0, 255), rnd.Next(0, 255));
g.DrawLine(new Pen(color), x1, y1, x2, y2);
}
Now I want to copy bitmap in Paint event. I do it like this:
void Form1Paint(object sender, PaintEventArgs e)
{
e.Graphics.DrawImageUnscaled(bitmap, 0, 0);
}
Hovewer, the DrawImageUnscaled copies pixels and applies the alpha channel, thus pixels with alpha == 0 won't have any effect. But I need raw byte copy, so pixels with alpha == 0 are also copied. So the result of these operations should be that e.Graphics contains exact byte-copy of the bitmap. How to do that?
Summary: When drawing a bitmap, I don't want to apply the alpha channel, I merely want to copy the pixels.
