PF_RGB -> PF_A8 -> GL_ALPHA

I want to load a pixmap in any format, convert the pixels to an PF_A8 alpha map, based on pixel brightness, and then create a GL_ALPHA texture from that.

Can someone explain how this works? Thank you.


PF_RGBA8888 -> PF_A8 -> GL_ALPHA does work, BTW, so it seems the faulty step is in converting RGB888 and I8 to A8.

Here's what you have to do. Just watch out for the following conversions that contain no alpha:

				If pixmap.format=PF_RGB888 Or pixmap.format=PF_BGR888 Or pixmap.format=PF_I8
					alphamap:TPixmap=CreatePixmap(pixmap.width,pixmap.height,PF_A8)
					For x=0 To pixmap.width-1
						For y=0 To pixmap.width-1
							color=ReadPixel(pixmap,x,y)
							r=(ReadPixel(pixmap,x,y) & %11111111)
							WritePixel alphamap,x,y,(r Shl 24)
						Next
					Next
					pixmap=alphamap
				EndIf

I usually take one of the channels and use it as the alpha channel. Otherwise you probably should properly do a grayscale conversion from color to grayscale and then use that as alpha.