I'm using an alpha bitmap to blit some button on a screen, and I'm getting a strange artefact. To test it, I created this bitmap:
http://www.techlogic.ca/aw/Button_EndTurn2.png
You will see the magenta doodle I made in the upper-right corner.
And here is the result, when using alpha blending, with no opacity:
http://www.techlogic.ca/aw/res.png
I resized the image to 8x its size so that we clearly see the artefact. I didn't touch the colors.
Granted, the artefact is not very heavy, but it still is an artefact, and is apparent sometimes.
I use AlphaBltFast, and no blitting flags with not structure.
Is this normal? Shouldn't this artefact be invisible since the bottom part of the source image (the alpha channel) contains RGB(0,0,0) at that location?
Thanks!