It's not working because it needs to be processed in a certain way, and Blitz3D only preprocesses masked textures like that when you load them with LoadTexture(). It doesn't process textures that you manually create.
The masked effect is really 'alpha-testing,' the technique used in masking: rasterized pixels of a mesh that have an alpha value below a threshold (usually 0.5) are discarded from rendering, and each pixel has their alpha values as the combination of the vertex colours, material colour and texture sampling.
The Blitz3D documentation says that the masking is based on the black colour, but internally it's really based on alpha values - at the moment of loading your masked texture, Blitz3D writes on the masked texture an alpha value of zero for all the black texels, and an alpha value of 1.0 for all the other texels.
This can be confirmed through experimentation.
So if you want a texture that you created yourself to have the masked effect working properly, you need to manually implement that same preprocessing that Blitz3D does.
Function MaskTexture( texture%, maskR% = 0, maskG% = 0, maskB% = 0 )
Local w = TextureWidth( texture ) - 1
Local h = TextureHeight( texture ) - 1
Local sampleRGB
Local maskRGB = ( maskR Shl 16 ) + ( maskG Shl 8 ) + maskB
LockBuffer( TextureBuffer( texture ) )
For y = 0 To h
For x = 0 To w
sampleRGB = ReadPixelFast( x, y ) And $00FFFFFF ;Sample from the texture, reset the sampled alpha value.
If sampleRGB = maskRGB Then
;The texel should be masked.
WritePixelFast( x, y, sampleRGB )
Else
;The texel is visible. Set a maximum alpha value.
WritePixelFast( x, y, sampleRGB Or $FF000000 ) ;
EndIf
Next
Next
UnlockBuffer( TextureBuffer( texture ) )
End Function Const FLAG_COLOUR = 1
Const FLAG_MASKED = 4
Local myTexture = CreateTexture( ..., FLAG_COLOUR + FLAG_MASKED )
CopyRect( ... ) ;Fill the texture with content.
MaskTexture( myTexture, 255, 0, 255 ) ;Mask with magenta colour, for example.
| 
