Re: Looking for colourful advice

[Florian Scandella <flo chilicode com>]

couldn't one just write a custom shader and set it for an actor? or is
the clutter shader api not supported by gnome-shell?

flo


On Mon, 2010-03-08 at 17:40 -0500, Owen Taylor wrote:
> On Tue, 2010-03-02 at 10:35 -0500, Joseph Scheuhammer wrote:
> > Hi,
> > 
> > Gnome-mag has a "cross-hair" feature for helping users find the mouse 
> > cursor.  An example graphic can be viewed here:
> > http://clown.atrc.utoronto.ca/aegis/GS-Mag/CrossHairs.png
> > 
> > The issue is that the cross hairs cannot obscure what lies beneath 
> > them.  As you can see in the png, the colours of the cross hair are 
> > blended with the background.
> > 
> > Is colour blending possible within GnomeShell?  My approach would be to 
> > use clutter texture objects to form the cross hairs -- are there colour 
> > blending functions for texture objects?  I've looked at the online 
> > documentation (http://www.clutter-project.org/docs/clutter/stable/), and 
> > found transparency manipulations, but that's probably not enough.  
> > Should I be diving into COGL?  Looking somewhere else?
> > 
> > Any advice would be appreciated.
> 
> To get this 'XOR' affect you'll need to go straight to OpenGL and use
> glLogicOp(). You can find examples of this with a web search. This will
> need to be done from C.
> 
> Two approaches to code organization:
> 
>  - You could write a custom clutter actor that draws this way
>    (Using cogl_begin_gl() and cogl_end_gl() around the OpenGL code)
> 
>  - You could paint the cross-hairs on top of the stage after the
>    stage is completely painted, similar to how shell-recorder.c
>    draws the recording icon and progress bar. (You still need
>    the cogl_begin_gl() and cogl_end_gl() calls.)
> 
> - Owen
> 
> 
> 
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