Draw a coloured stencil mask

BlitzMax Forums/OpenGL Module/Draw a coloured stencil mask

beanage

(Posted 2010) [#1]

Hey,

I would like know, whether there is an easy-ish OpenGL way to do this.
Here is an illustration of my problem:

Please consider I want to avoid using shaders too.

ImaginaryHuman

(Posted 2010) [#2]

So you basically want to draw all colored pixels as white pixels?

beanage

(Posted 2010) [#3]

So you basically want to draw all colored pixels as white pixels?

Not necessarily white, but uniform. Its for a secondary support buffer in a 2.5D game, where a pixel should identify the object occupying it by its color.

ImaginaryHuman

(Posted 2010) [#4]

Hmm. One way it so use the stencil buffer. Set it to draw to the stencil where there are accepted alpha values in your image, then use the stencil and draw a solid-color rectangle over the top of the sprite to fill it in.

beanage

(Posted 2010) [#5]

That seems like a rather good idea!
So heres some pseudocode assembled from my understanding of your idea:

'Initialization
'--------------
- Create Stencil Buffer
- Clear Stencil Buffer

'Main Loop
'---------
- For Each visible "Object"
-	Set Stencil Buffer drawing Mode to Alpha Stencil or something
-	Draw the Image of the "Object" (to the stencil buffer or straight to the backbuffer?)
-	Make the stencil buffer stenciling
- 		set an FBO for the target buffer
-			Draw a rect with the individual color of "Object"
-		close the FBO
-	Clear the stencil buffer