[SDL] refreshing my knowledge

Roger D. Vargas roger at eht.scu.tur.cu
Mon Jan 13 05:51:01 PST 2003


On Sun, 12 Jan 2003, José Luis Sánchez wrote:

> "Roger D. Vargas" <roger at eht.scu.tur.cu> escribió:
> 
> > I would like to confirm some things about blits:
> > 
> > video ram to video ram blits are faster
> > writing directly to vram (ie. modifying pixels) is very slow.
> > system ram to video ram blits are a bit slower
> > 
> > There is some difference if there is support for accelerated blits?
> 
> The scenario is actually somewhat more complex.
I know, but the idea is to give some "quick guides" about blitting.

> Note that the GPU might be actually SLOWER than the main CPU.  In fact, the
> FASTEST blits are from system RAM to system RAM.  Just remember: the 
goal is to  
> use CPU cycles as little as possible.
So, we can consider that if we have to do a lot of blits, we better put 
the surface in the system memory and blit the final result to vram?
Another question, where is located the surface returned by SetVideoMode?
> 
> Loudly, those cycles are wasted if you simply keep your CPU waiting for the
> blit to be completed.  So you might design your program so that it does
> actually something useful while the GPU is busy.
And how can I do this? How can i process something while Im blitting?

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