[Mesa-dev] [RFC] st/vega: Clean up and OpenVG 1.1

Chia-I Wu olvaffe at gmail.com
Tue Nov 30 01:51:33 PST 2010

Hi list,

I have spent the weekend adding OpenVG 1.1 support to Vega state
tracker.  The new features added include mask layer support, text
support, and a new color transformation stage.  The work can be found


vega-1.1 branch is based on another clean-up branch


Vega employs a renderer to submit its rendering commands to the pipe
context.  vega-polish branch mainly introduces "states" to renderer.
I feel vega-1.1 is more self-explanatory so I will focus more on

The idea of renderer states is that, functions like vgClear or vgMask
submit rendering commands to the pipe context, but they do not want to
go through the standard OpenVG pipeline.  Instead of having them
handle the pipe states save/restore, renderer states allows them to
switch the renderer to the specific state they need.  For example,
vgClear can then be implemented by

  renderer_clear(renderer, x, y, w, h, color); // clear a rectangle

vgClear does not need to know which pipe states renderer_clear_begin
sets or which pipe states renderer_clear_end restores.  Nor should it

After the addition of renderer states, vega-polish goes on to refactor
the code in a way that finally the renderer no longer depends on
OpenVG states and all pipe context state manipulation is done by the
renderer.  This makes the renderer an abraction of the pipe_context
for Vega:

   App -> OpenVG -> renderer -> pipe_context

The benefits of the changes are that code that handles OpenVG
functions and code that sets pipe_context is no longer mixed.  Since
the renderer is an opaque object, its implementation can be changed:
Use a different pipe_context function for an OpenVG function or the
frequency of pipe state changes may be minimized.

Demos for OpenVG 1.1 features have been committed to the demo
repository.  I've also commited several functional tests while working
on vega-polish.  I do not have other conformance tests, but no
regressions are found for our OpenVG demos (which might not say
too much...).


olv at LunarG.com

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