Re: [Dri-devel] How to trace switching to software rendering

[Brian P. <br...@tu...>]

Michael Schlueter wrote:
> Hi Brian,
> 
> sorry for disturb you again.
> 
> Am Sam, 2002-06-22 um 00.00 schrieb Brian Paul:
> 
>>Most of the DRI drivers have a per-context field called 'Fallback'.
>>It's a bitmask which records various reasons why we need to fallback
>>to software rendering.  In the case of the mga (G400) driver you'll
>>see these flags in mgacontext.h:
>>
>>#define MGA_FALLBACK_TEXTURE        0x1
>>#define MGA_FALLBACK_DRAW_BUFFER    0x2
>>#define MGA_FALLBACK_READ_BUFFER    0x4
>>#define MGA_FALLBACK_LOGICOP        0x8
>>#define MGA_FALLBACK_RENDERMODE     0x10
>>#define MGA_FALLBACK_STENCIL        0x20
>>#define MGA_FALLBACK_DEPTH          0x40
>>
>>If you search the code, you'll find where we set these flags by
>>calling mgaFallback() (via the FALLBACK() macro).  You could put
>>a printf in there to print the bit value and get an idea of what's
>>slowing you down.
> 
> 
> Ok, I did a printf there and switch MGA_DEBUG on. Now I need a bit help
> with the analyse of the output...
> 
> mgaFallback: bit:1 mode:0
> 
> Looks like this is a call from mgaUpdateTextureState. Since mode is 0
> the fallback flag is unset? 
> 
> FLUSH_BATCH in mgaReadDepthPixels_16
> FLUSH_BATCH in mgaWriteDepthPixels_16
> FLUSH_BATCH in mgaWriteRGBAPixels_565
> FLUSH_BATCH in mgaDDBindTexture
> FLUSH_BATCH in mgaDDUpdateHwState
> FLUSH_BATCH in mgaFallback
> FALLBACK: GL_DECAL RGBA texture, unit=0
> FLUSH_BATCH in mgaReadDepthPixels_16
> FLUSH_BATCH in mgaWriteDepthPixels_16
> FLUSH_BATCH in mgaWriteRGBAPixels_565
> 
> This looks more interesting to me. Is there a problem with RGBA
> textures?

Without looking at the code, my guess is that the GL_DECAL env mode
with an RGBA texture probably isn't implemented in hardware.  Hardware
from that era often had limitations that prevented some combinations
of texture env modes and texture formats from being done in hardware.

If you look at the mga code you'll probably find a comment and more
info.

-Brian