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Journeyman III

Conservative Rendering


   I need for my application that every drawing produce at least one pixel output (even if this is an empty triangle = 3 identical points). NVidia have an extension (GL_NV_conservative_raster) to enable such a mode (on Maxwell+ cards). Is there a similar extension on AMD cards ?



3 Replies

Hi Tof,

Some of our hardware can support functionality similar to that in the NVIDIA extension you mention, but we are currently not shipping an extension of our own. We will likely hold off until we can come to a consensus with other hardware vendors on a common extension before exposing the feature, but it will come in time.

I should note, however, that GL_NV_conservative_raster doesn't do exactly what you want.

Specifically with regards to:

tof29 wrote:

... (even if this is an empty triangle = 3 identical points).

See issue (2) in the NVIDIA specification:

(2) Do zero area primitives generate fragments in conservative raster?

  RESOLVED: No, although in some cases that may not be the desired behavior.

  If a primitive is truly zero area (e.g. two vertices of a triangle have

  identical positions), then drawing nothing is probably fine. If the

  primitive happens to be zero area due to subpixel precision then generating

  fragments may be desirable, but this spec does define that behavior.



Thanks for your answer. In fact, It was 3 identical points in final pixel coordinates, but 3 different points in vec(x,y,z).

I need this because I must not loose any data information when displaying critical information. For now, I have a workaround using Geometry Shader to make sure my triangles are at least more than one pixel size at any distance.

Is there any time frame for this extension to be release ? Will it be supported by the E8860 card ?




For obvious reasons, we can't answer a question about when something is going to show up. Particularly in this case because it is an open standard, and we're dependent not only on our own engineering, but other companies as well.