[Openicc] questions about Compiz

[Hal V. Engel]

On Sunday, January 30, 2011 01:17:45 pm Jan-Peter Homann wrote:
> Hello Kai-Uwe, Richard and all,
> 
> I have following questions about Compiz:

Compiz is a composting system for use with X11.  Its job it to compost output 
from applications into the display space of what ever screens are in use on a 
system.  It also supports various on screen effects by using plug ins.  Many 
plug ins are shipped with Compiz but many others are from 3rd parties.  

> 
> Wich kind of color transformations are supported from Compiz:
> - RGB 2 RGB
> - CMYK 2 RGB
> - RGB 2 CMYK 2 RGB

Compiz assumes that everything handed to it is device RGB and it does not know 
how to do color space transforms at least in the sense we use that terminology 
and in it's default state knows nothing about CM.  

In order to make Compiz handle color transformations OpenICC had a GSoC 
project to write a Compiz plug in named CompICC that converts application 
supplied display output (windows, borders, menus, images...) which is always 
in RGB format (because the app assumes it is talking to the composting engine) 
and transforms this output to device RGB for what ever device that output will 
be displayed on and hands this to Compiz to compost onto the display. 

> 
> Would it be able to implent a rendering to fileout
> - RGB 2 CMYK
> - CMYK 2 CMYK
> (Fast rendering of Bitmaps for Printout)

This is outside of the scope of Compiz since it part of the display pipe line.

> 
> What are technical problems and possible solutions for a wide usage of
> Compiz ?
> 

The biggest issue with Compiz and composting software is generally the GPU 
hardware and drivers which vary in how fast these can do things and also in 
how well these implement the high level graphics API that is being used by the 
composing engine.  In the case of X11 systems and Compiz this is OpenGL.    

There is a considerable amount of variation in the quality of current OpenGL 
implementations in X11.  Some video card drivers have limited (in some case 
no) OpenGL support well others have excellent support (nvidia cards with the 
proprietary drivers for example).  Compiz will run nicely on a high end nvidia 
GPU with recent drivers but will not run at all on some older hardware and 
with some video card drivers. 

The situation is improving as modern GPUs are very powerful (even the less 
expensive hardware is powerful relative to what was available a few years ago) 
and the quality of the drivers, at least for more recent hardware, has gotten 
much better in recent years.  For example a few years ago the ATI (now AMD) 
X11 drivers where  pure crap.  After AMD purchased ATI the situation has 
changed and their driver is close to nvidia's quality and they are steadily 
closing the gap.  Open source drivers have also been improving and AMD is 
supplying technical support to the open source community (nvidia is not 
however) and the open source drivers for this hardware have improved 
dramatically in the last few years.   Intel actually only supplies open source 
drivers for X11 systems for their GPU hardware.  Intel GPU hardware is 
generally less powerful than nvidia and AMD GPU hardware but their drivers 
have generally been very good recently.  Side note the video that was recently 
talked about here was a presentation by Keith Packard who is one of the 
developers of these drivers for Intel.

Compiz or something like it (like kwin) will be used more widely on X11 
desktops as all of these things mature.  As GPU hardware gets more powerful 
and OpenGL support gets better more users will be using a composting system.

> 
> Thanks and best regards
> Jan-Peter