Save alpha channel from buffer to file?

Blitz3D Forums/Blitz3D Programming/Save alpha channel from buffer to file?

chi	(Posted 2009) [#1]

I know it´s not possible with SaveBuffer (only 24bit .bmp) but there has to be a way, right?

Graphics3D 800,500,0,2

cam=CreateCamera()
CameraClsColor cam,128,128,128
PositionEntity cam,0,0,-5

cube=CreateCube()

tex=CreateTexture(256,256,1+2+8)

For y=95 To 159
	For x=95 To 159
		WritePixel(x,y,0 Shl 24,TextureBuffer(tex))
	Next
Next

EntityTexture cube,tex

Repeat
	TurnEntity cube,.1,.1,.1
	RenderWorld
	Delay 10
	Flip
Until KeyHit(1)
End

thx, chi

Warner

(Posted 2009) [#2]

Maybe you could save a black&white bitmap that contains only the alpha channel. Or you could save the data to a file, and then import it as 'raw' format.

_PJ_	(Posted 2009) [#3]

Yeah I think Warner's on the right track... some form of:

(sorry, only pseudo code cos I dont have Blitz handy at the mo)

Function SaveAlpha(Buffer,FilePath$)

Local OriginalBuffer=GraphicsBuffer()
SetBuffer Buffer
Local W=GraphicsWidth()
Local H=GraphicsHeight()
Local X,Y,C,A
Local File=WriteFile(FilePath$)
;Maybe necessary to ensure the dimensions of the buffer are kept
WriteInt File,X
WriteInt File,Y
For X=0 to W-1
For Y=0 to H-1
C=ReadPixelFast(X,Y)

A=GetAlpha(C); This would be some kinda Hex-fiddling to get just the a from the aRGB :)
WriteInt File,A
Next
Next
CloseFile File
SetBuffer OriginalBuffer
End Function

Floyd

(Posted 2009) [#4]

If the question is about saving a texture with alpha then try Save tga.

I just noticed this is entry #1 in the code archives, from 2001.

chi	(Posted 2009) [#5]

yeah, thank you! SaveTga is working for me ;)
don´t know why i couldn´t find this c.a.entry by myself??

thx 4 help, chi