View Full Version : Question about Point Sprite

04-12-2006, 05:31 PM
I am expirementing with point sprite and I am not sure if I am reading the spec correctly or not.

According to the spec, it says if MULTISAMPLE is enabled and the value of SAMPLE_BUFFERS is one, then POINT_SMOOTH is ignored.

I take it that if I enable multisample and if the SAMPLE_BUFFER is 1, then I'll still see a point sprite regardless if I have POINT_SMOOTH enabled or not. However, if I don't enable multisample and I have POINT_SMOOTH enabled, then I should see an anti-aliased point.

In my NiVidia card, it didn't care if I enabled multisample and check the SAMPLE_BUFFER. It would just ignore the POINT_SMOOTH enable call and only render point sprite once I have the POINT_SPRITE enabled.

Am I reading the spec correctly? Or once I enabled the point sprite, I can expect POINT_SMOOTH is always ignored regardless if I have multisample enabled or not.

04-13-2006, 01:14 AM
POINT_SMOOTH (antialiased points) affects only the standard point rendering.
Multisampling affects the rasterization rules of antialiased primitives.
Enabled point sprites override the standard point rasterization. They are always rectangular and you need to care about the shape with textures.

Directly from the OpenGL 2.0 spec chapter 3.3 page 96:
"Point sprites are enabled or disabled by calling Enable or Disable with the symbolic constant POINT SPRITE. The default state is for point sprites to be disabled.
When point sprites are enabled, the state of the point antialiasing enable is ignored."

04-13-2006, 09:56 AM
Thanks for the info.