Premultiplied Colour Blending

[sq4]

Purebasic gives the possibility to display a sprite in a certain monochrome color.

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DisplayTransparentSprite(#Sprite, x, y [, Intensity [, Color]])

The idea behind this (IMHO) must be to display it in combination with the same sprite in a certain blending mode to colorize.

Most of the time this works! So, I must be on the right track...
But something is weird and I think it has to do with the fact that the monochrome colored sprite's RGB component isn't premultiplied with it's alpha component.

Let me explain:

I draw the original sprite first like this

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SpriteBlendingMode(#PB_Sprite_BlendSourceAlpha,#PB_Sprite_BlendInvertSourceAlpha)
DisplayTransparentSprite(#Sprite,x,y,Alpha)

And then I layer the same sprite over it like this

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SpriteBlendingMode(#PB_Sprite_BlendDestinationColor,#PB_Sprite_BlendInvertSourceAlpha)
DisplayTransparentSprite(#Sprite,x,y,255, Color)

I can also use this for the second sprite :

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SpriteBlendingMode(#PB_Sprite_BlendDestinationColor,#PB_Sprite_BlendInvertDestinationAlpha)
DisplayTransparentSprite(#Sprite,x,y,255, Color)

Both methods give different results depending on the ClearScreen(Color).

So my questions :
- Is it true that Purebasic monochrome colored sprites are ment to be used for color compositing?
- Why no premultiply?


Hope this makes sense...
A nice explanation what I try to achieve :
http://amindforeverprogramming.blogspot ... nding.html