[SDL] SDL 1.3 on Mac OS X speed hit
slouken at devolution.com
Tue Aug 14 21:09:48 PDT 2007
> > Performance notes coming shortly.
> - Every call to SDL_SelectRenderer() appears to result in a MakeCurrent
> call, even if we haven't changed GL contexts, and even if there's only
> one GL context total. The high-level SDL call should cache the last
> selected renderer and return immediately if the new selection matches
> the old one. There are platforms where making a GL context current is
> extremely expensive, probably even if it's already current.
> MoveSprites() in testsprite2.c is doing this when there's only one window.
Okay, this is implemented.
> - Never never call a glGet*() entry point if you can avoid it, including
> glGetError(). In the new multithreaded GL on Mac OS X 10.5 (and some
> existing 10.4-based hardware), this will force all threads to
> synchronize, basically nullifying the multithreading boost, even if you
> just call glGetError() once a frame. glGetError() is mostly good for
> detecting programming errors and not runtime states, so you can live
> without it in production code (#ifdef _DEBUG those sections), state you
> set yourself should be shadowed in local variables instead of retrieved
> from glGetInteger(), etc, or queried once at startup for things like the
> max texture size.
I'll switch this over once the VBO/PBO stuff is done.
> - Turn on the multithreaded GL. :) Here's the code:
All set, pending VBO/PBO changes to take advantage of it.
> - Don't use glBegin()/glEnd() to put polygons to the screen. Apple
> engineers implied that just having a vertex_buffer_object with one
> rectangle in it will be faster, since there's all sorts of state that
> has to be built, coordinated, pushed to the hardware, and immediately
> discarded every time in a glBegin/glEnd pair.
I did a test on Windows OpenGL last year, and it was a wash. I opted to
leave it as glBegin and glEnd for simplicity, but since it's much better
on Mac OS X, yes let's use a VBO.
> - Keep track of state you've set, only set it when it changes (if
> texture X is already bound to target Y, calling glBindTexture(Y, X) is a
> waste of time). Not all GL implementations are smart enough to make
> these into no-ops. This is probably a small win overall, though.
Once the VBO/PBO stuff is done I'll go through and clean this up. I'll
wait until then since I'm not sure how much code will change between now
-Sam Lantinga, Lead Software Engineer, Blizzard Entertainment
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