Zirzlaff, Torsten wrote:
> I stumble over following and wonder what might be the reason or even
> the problem
> At home I have Radeon9200 PCI with 12MB with dri enabled (Debian
> Sarge on an AXP-system) and in the office a Radeon 7500 AGP in a W2K
> system with cygwin.
> When I run the glxinfo -l on my home-system the
> GL_MAX_ELEMENTS_VERTICES limit is 3000 on the system at home (DRI
> build from CVS last weekend).
> Surprisingly the value for GL_MAX_ELEMENTS_VERTICES on the office
> system (X.org) returns a limt of 2147483647 for
> Is the cygwin value just a dummy with an arbitay high number or for
I suppose X.Org running on cygwin/w2k is using the underlying
ati/windows OpenGL driver. That GL_MAX_ELEMENTS_VERTICES (and
GL_MAX_ELEMENTS_INDICES) is just a performance hint, and ATI's OGL
implementation seems to suggest that there is no performance hit when
using insane amounts of vertex data per vertex array. By the way, these
two constants are only relevant for glDrawRangeElements. The mesa-based
r200 DRI driver though unfortunately indeed can't deal with large
amounts of vertex data efficiently, since all vertex data must fit
within a single buffer (64KB - actually, 3000 vertices won't fit in a
single buffer, not even close, and it's my understanding this is the
primary reason why lockups occur when multiple OGL apps are run
> If it's real why have the 9200 such a low limit,
It's a driver limit, not a hardware one. The hardware can deal with
65536 vertices and indices directly, I believe.
> which I assume to be
> the major reason why my system breaks down on large OpenGL scenes
> with more than 2000 polygons.
It could be a reason. There also seem to be performance problems with
current CVS and vertex arrays, for some reason ut2k3 burns about 6 times
more cpu cycles in that ArrayElement handling than it did in XFree86
4.3.902 - it could be specific to something that ut2k3 does however, not
a general problem. For the record though, the XiG Summit driver
announces GL_MAX_ELEMENTS_VERTICES of 4096 and GL_MAX_ELEMENTS_INDICES
of 32768, and as far as I can see it handles scenes with lots of
polygons very well. There's just no way a driver handles 2 billion
vertices efficiently anyway, that would require about half a terabyte of
ram just for the vertex data ;-).
You also have a PCI 9200 - there are known performance problems (with
unknown reasons...) with pci based r200/rv250 cards and the DRI driver.