On Tue, Sep 14, 2010 at 12:30:48 -0400, buginator wrote:
On 9/13/10, Giel van Schijndel wrote:
This however, would require significant changes to the drawing code.
Keep in mind that these changes would be required for *pure* OpenGL 3.0
as well, with pure meaning without the backward compatibility
extensions. The two most significant changes are:
* immediate-mode drawing would have to go (glBegin()/glEnd()),
replacing it with either VAs or VBOs
I am fine with this.
- in OpenGL ES the matrix stacks don't exist anymore, so we would have
to maintain this stack outside of the OpenGL API (relatively easy to
do)
This is also needed for proper support of LoD, occlusion culling, and
some other things. I am also fine with this.
- fixed pipeline rendering is mostly gone, so a shader performing the
vertex transformation (multiplication with model-view and projection
matrices) would have to be used.
The only real concern I have is driver support, on all the platforms
we support.
Right, this is largely due to the complete removal of all matrix-related
functions from the API. The only API function still handling matrices is
glUniform.
Thus the only way of getting matrix multiplication in OpenGL ES 2.0 is
by means of reimplementing that part of the fixed function pipeline in
GLSL. If done properly this shader probably wouldn't be required on
systems that still have the fixed function pipeline.
Please give me your thoughts on making these changes. Personally I
don't think removing of immediate-mode rendering is a very big deal, nor
is replacing gl(Push|Pop)Matrix with our own implementation. Completely
shedding our dependence on the fixed rendering pipeline is something
of an entirely different scale though.
A rewrite of the gfx engine is need, since most of it is still done
with the brute force approach. Getting rid of the fixed pipeline was
on my long term TODO list anyway. :)
Would this be done directly in trunk, or would a new branch be made for this ?
Since I see you started working on the 'easier' stuff, did you have a
timeframe when all this would be done ?
Definitely trunk since I expect that most (hopefully all) changes can be
done incrementally, and thus without disturbing trunk too much. As for
a time frame, I haven't thought about that yet, my intention was just to
code till completion.
PS OpenGL ES 1.1 *does* support the fixed function pipeline but has no
support for the programmable pipeline, so is IMO not a good option at
all.
--
Giel
--
There are 2 hard problems in computer science: cache invalidation,
naming things, and off-by-1 errors.
-- Leon Bambrick
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