Compositing and color modulation

Would anybody happen to have an example about color modulation using CompositeTags()?

@Capehill

Stupid question time: what do you mean by Colour modulation?

[edit]
(PS knowing how these things can get misread the stupid question is mine not yours)

Googling the term throws up all sorts of things most of which related shading models and stuff (real physical models made of plastic, with enamel paint and so on...)

@broadblues

I try to modify texture by ARGB multipliers. Here is some code:

https://sourceforge.net/p/sdl2-amigaos ... render_compositing.c#l754

However, it looks like modulation would be ignored.

@Capehill

Hmm okay not used that feature, it's not mentioned in the autodoc.

The obvious thing to check is that your flags do really include the COMPFLAG_Color1Modulate option.

@Capehill

Have you tried setting COMPFLAG_ForceSoftware? Maybe it's just the driver for your gfxcard that doesn't support the modulate feature?

Note that the software composite code doesn't support vertex arrays though.

@salass00
Quote:
None of the drivers support this feature. It's not in the autodocs either, so I think that this was a feature that didn't make the final cut. We should probably remove the definitions in the headers to reflect this.

Hans

@Hans

There is at least some code for dealing with the COMPFLAG_Color1Modulate flag in the software fallback for Composite() so it's not completely unimplemented.

Maybe it just wasn't a priority to implement in the hardware drivers because nothing needed it at the time?

As Hans wrote color modulation dont works
The only way to obtain a similar effect is to have a small bitmap (say 4*4 pixels) that you fill with your color then do a transparent CompositeTags to apply this translucent colored rectangle to the area you want to color-modulate
This may works for rectangular surface (ie highlight a button) but for a "sprite" it may be complicated to exclude the transparent parts (=it will need a buffer bitmap and one more CompositeTags )


Alain Thellier

Note: using a (say) 4*4 pixels bitmap will avoid problems with filtering "catching" surrounding (black, non existents) pixels that will happen if you use a 1x1 pixel bitmap.

Note2: I mean use a 4x4 bitmap but composite on the 2x2 inner

@thellier

Yeah, I suppose there has to be a secondary bitmap allocated if application requests color modulation for a given texture.

So:

1) original texture x*y
2) "modulator" texture (like 4*4)
3) resulting, "modulated" texture x*y, that will be displayed after magic dust falls

Note3:
Also the 2x2 pixels may be different colors so used with filtering may serve to create color gradients

Alain Thellier