GL_POINT_SMOOTH on Intel 945GM
sroland at tungstengraphics.com
Fri May 4 05:44:02 PDT 2007
Rogers Simon wrote:
> Xorg 7.1.1 on Centos 5.0 using I810 driver and DRI enabled.
> Enabling GL_POINT_SMOOTH slows a simple openGL filled quad application
> from hundreds of FPS to less than 10.
> Is this a bug or a feature? Can't the Intel chipset do antialiasing?
Large smooth points are something rarely implemented in hardware, almost
no chip can do that (in fact I don't know of a single one which can,
maybe some old workstation-class card could, or very new cards
supporting geometry shaders should be able to too). Drivers (closed or
open) use all sort of workarounds for making that feature available,
ranging from just announcing a max point size of 1.0, drawing points as
textured quads with alpha test hacks (sometimes resulting in bogus
output), to probably just replace the point with a bunch of tris.
An unconditional fallback to swrast even when no points are drawn
(either explicitly or by using point polygon mode) doesn't look like a
very good solution, but I think the newer i915tex driver would fix that.
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