View Full Version : Issues with "Pixels per Polygon" render SubDiv

09-30-2009, 04:29 AM
Hello all,

Hope you're all well. I have a problem with the "Pixels per Polygon" subdivision in LightWave 9.6 (win).

Basically - it doens't seem to work; or at least work very well.

I believe first and foremost that it only works with Catmull-Clark subdivisions; not with the old SubPatch mode.

However, it doesn't seem to work very efficiently. I have been trying to use it to do landscapes with a very high level of subdivision; e.g. driving the "Pixels per Polygon" value down to 1. However it seems to create VAST numbers of polygons in this mode; with the landscape in the far distance being subdivided far too much, and areas outside the field of view of the camera being subdivided. Pretty soon you run into the memory limit and it crashes.

It seems that in fact the "Pixels per Polygon" value set to like 5 or 6 gives you almost 1 polygon per pixel. Certainly, setting the value to 5 gives you a totally solid mesh if you view it with wireframes (set via the surface panel).

Has anyone had any success with this technique? Right now it seems basically it doesn't work.



09-30-2009, 07:53 AM
I have made one traditional sub-patch 1x1 meter size. Then saved object and send to Layout. Used Pixels Per Polygon 1.0, and when it was far far from camera, it was generating 32 polygons in Render Stats, then moved closer to camera, generated 2,000 polys, then very close- 4,000 polys or so.

So, from my experience, tested 3 minutes ago, it's working with Sub-Patches, and is respecting distance to camera no problem..
Mesh that's outside of field of view, obviously must be sub-divided too, because it might be seen from reflective surfaces.

09-30-2009, 08:25 AM
Same here, it caused massive system hangup so I gave it up.
I tried William's weight map driven subdivision technique with better results but still it's quite diffiicult to handle. Have to check CC subdivs though.

09-30-2009, 04:20 PM
You can use a gradient with Distance to Camera to make sure the subdivision isn't global to the object, but obviously it doesn't show in Layout. Here's a 10-second example (using Render Wireframe mode). The clipboard image png shows the gradient editor. There are still issues in that the original geometry needs to be subdivided to "guide" the further APS subdivision, so my original plane was 3x11 polys, but then I just used standard subpatches.


09-30-2009, 04:24 PM
You have to be careful that you have enough geometry to 'step' through progressive subdivisions to get what you want. For example, two adjacent cage polygons can't be subdivided to more than one level apart, ie one can be subdivided twice, the other can be subdivided only once or four times.