Extracting Alpha Bit from a texture

Blitz3D Forums/Blitz3D Beginners Area/Extracting Alpha Bit from a texture

Stevie G

(Posted 2004) [#1]

I'm creating texture with alpha flag set. I have drawn text directly to the texture which I assume will have a default of 0. I can iterate through the texture pixels and pick up all non-black pixels but I then need to apply full alpha to them so that they can be seen. I know there should be $FF for the left most bit in this case but how do I add it.

Say I use argb=readpixel(x,y,texture) how do I add the $FF to the result, bearing in mind I'm only using 16bit colors?

Ross C

(Posted 2004) [#2]

i'd image it would be 4 bits each then for RGB and A

Stevie G

(Posted 2004) [#3]

Thanks. I'm at work Ross so can't try this. So I would just use newargb = argb and $FF000000?

Ross C

(Posted 2004) [#4]

I asked about on IRC channel. I'm not really sure what the answer was, so i can't really help you any, sorry m8 :(

[EDIT] It appears that you just write to it the same way you would write to a 32 bit texture :)

N	(Posted 2004) [#5]

Not sure if this will help, but here's some code to return integer/'normal' color values (from Vein).

Const RALPHA = 24	;Return Alpha when using RColor
Const RRED = 16	;Return Red when using RColor
Const RGREEN = 8	;Return Green when using RColor
Const RBLUE = 0	;Return Blue when using RColor

Function IntColor(R,G,B,A=255)	;Usage: WritePixelFast X,Y,IntColor(Red,Green,Blue,Alpha) or C = IntColor(Red,Green,Blue,Alpha) : WritePixel X,Y,C
	Return A Shl 24 Or R Shl 16 Or G Shl 8 Or B Shl 0
End Function

Function RColor%(c%,d%)	;Usage: Red = RColor(ReadPixelFast(255,127),RGREEN)
	Return c Shr d And 255 Shl 0
End Function

Uncle

(Posted 2004) [#6]

Hi,

I've been working on something similar, and came up with the following :

;ARGB Functions by Rob Farley 2003
;rob@...
;http://www.mentalillusion.co.uk
;updated by Andrew Nixon Feb 2004 to include read and write alpha


Function read_r(x,y,image_name)
argb=ReadPixel(x,y,TextureBuffer(image_name))
Return (ARGB Shr 16) And $ff 
End Function

Function read_g(x,y,image_name)
argb=ReadPixel(x,y,TextureBuffer(image_name))
Return (ARGB Shr 8) And $ff 
End Function

Function read_b(x,y,image_name)
argb=ReadPixel(x,y,TextureBuffer(image_name))
Return ARGB And $ff
End Function

Function read_a(x,y,image_name)
argb=ReadPixel(x,y,TextureBuffer(image_name))
Return (ARGB Shr 24)  And $ff
End Function


Function write_argb(x,y,a,r,g,b,image_name)
argb=(b Or (g Shl 8) Or (r Shl 16) Or (a Shl 24))
WritePixel x,y,argb,TextureBuffer(image_name)
End Function

Hope this helps,

Cheers,

Unc

Stevie G

(Posted 2004) [#7]

Thanks folks - managed to fix this by just using the argb from readpixel "or $ff000000" which works.

It's a bit of a pain that when using flag 2 to create a texture that it does not read any argb at all for the text I print on it. The argb value is always 0 for some reason.

I had to temporarily write text to an image and readpixel from this to ensure I got an argb > 0 to add alpha too.

Not sure if that made any sense but is there a way of doing this without using that temp image?