C# 2.0, GDI+ images & opacity

And don't know if this post belongs to this forum, but i'll ask anyway...

I'm making a small game as a test with GDI+ (C# 2.0). I had this question: is there an easy way to draw an Image object to Graphics with different opacity

I don't mean the transparency key thing, but the whole image should be half visible, and trasparency color of course not visible at all. I managed to alter the opacity of the image with getpixel and setpixel, but I'd like to know if there was a way to avoid pixel manipulation (since it takes time).

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C# 2.0, GDI+ images & opacity

Ivan Ooi
Great!

Thank You very much for the answer.

btw, Is there some documentation available, where I can check which element means which 4x4 matrix i would understand (RGBA), but 5x5 what is the fift element ( )
Sherrill34643
Some of DrawImage methods take an ImageAttributes parameter. The ImageAttributes class has a method called SetColorMatrix. Using that you can do anything with the colors of your image including modifying the alpha channel.

For your case I think the following color matrix sould do:

private static ColorMatrix colorMatrix = new ColorMatrix(
new float[][]
{
new float[] {1, 0, 0, 0, 0},
new float[] {0, 1, 0, 0, 0},
new float[] {0, 0, 1, 0, 0},
new float[] {0, 0, 0, 0.50f, 0},
new float[] {0, 0, 0, 0, 1}
});

Note the 0.5f value. That's the opacity.

protected void DrawTransparentImage(Graphics g, Rectangle rc, Image image)
{
using (ImageAttributes attrs = new ImageAttributes())
{
attrs.SetColorMatrix(colorMatrix);

g.DrawImage(image, rc, 0, 0, image.Width, image.Height,
GraphicsUnit.Pixel, attrs);
}
}
sumesh_tewatia
Check this out

http://msdn.microsoft.com/library/en-us/gdicpp/GDIPlus/usingGDIPlus/recoloring.asp frame=true

it should answer your questions.
andyboy
Thanks again
C# 2.0, GDI+ images & opacity

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