[SDL] Hardware surfaces under linux

[Bob Pendleton]

ates x wrote:
> 
> hi again!
> 
> first of all thank you for your fast reply!
> 
> > ...
> > 3D on the other hand has much higher, and I do mean
> > MUCH
> > higher performance requirements. You get the power >
> for
> > 3D mostly from the video card with help from the
> > CPU and
> > a lot of help from the AGP bus. Getting help from
> > the video
> > card requires a driver that know how to make the
> > best use
> > of the video card. The internals of each videocard
> > is
> > different from every other video card. So you need
> > special
> > drivers for each video card. The driver usually
> > includes
> > support for OGL, often it includes a custom
> > implementation
> > of OGL whose internals are customized for the video
> > card.
> 
> bob, that's not 100% correct. the driver adds
> extensions and tweaks the implementation.
> there's (afaik) no custom implementation for each
> vendor ;-)

At the driver level it is unique for each vendor with
tweaks for each video card. I spent 5 years writing
high performance drivers for 3D video hardware.

> anyway, be aware that opengl does nothing have to do
> with 3d performance.

Where did you get that idea? The API has a number of
design features that are specifically designed to make
it possible to implement it efficiently on a lot of
different hardware. The specific implementation for a 
specific piece of hardware has a dramatic effect on
performance. 

Companies have (SGI, IBM, HP...) have spent hundreds
of man years customizing the internals of their 
implementations of OpenGL to get high performance.
They have modified the internals of their OSes. They
have changed the designs of busses and processors.
They have even changed the way their compilers call
subroutines and how their linkers work. 

> and also keep in mind, that opengl (sdl does the same
> for 2d) is a unified api for different rendering
> hardware.

Very true. I'm well aware of this.

> 
> > So, it makes sense for SDL to use what ever version
> > of OGL
> > is available on the computer it is running on.
> 
> of course, it makes sense. but that's not the point,
> isn't it?
> 
> > Including
> > Mesa would only give you a version of OGL that is
> > equally
> > slow on every computer.
> 
> that's not correct either, bob. it depends on the
> system (cpu architecture, graphics card, os, ...).
> nevertheless, i can't think of an sdl-developer, who
> aims to write a game, which runs on a system with
> linux recently slower or faster than with windows on
> the same system.

I'm sorry, I can't make sense of this statement. I
suspect you are not a native english speaker and that
you have taken my use to "equally" to mean "exactly
the same" which would make what I said seems pretty
ridiculous. I will try to be more precise in the 
future.

What I was trying to say is that the software rendering
based, machine and OS independent, version of Mesa will
perform poorly compared to a hardware accelerated version
of OGL, on any given machine.

> 
> >
> > Warning: what I just said is a very high level
> > overview
> > as I see it. YMMV
> >
> >               Bob Pendleton
> 
> what does YMMV mean?

Your Mileage May Vary. It is a reference to television
commercials for car where they make claims about how
many miles per gallon a car will get. And then they
put in the phrase "Your Mileage May Vary" to keep from
being sued when real people with real cars don't get
the advertised mileage. Of course, this phrase points
out the fact that the US still uses miles and gallons
when all most all the rest of the world uses kilometers
and liters.

> 
> l8ers,
> Tolga.
> 
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