View Full Version : render subpatch level - Crashing

08-10-2006, 07:38 AM
Grrr this is annoying as ****..

but for me if i have a hi poly object and change the render subpatch level to
per object and anything above level 4 crashes !!

any tips or advice would be great


08-10-2006, 07:43 AM
Are you using Catmull-Clark? If so level 4 is probably waaay to high. CC subdivisions produce a LOT more polys than LWsubpatch.

Dave Jerrard
08-11-2006, 07:59 AM
Yes, CC's are definitely something to be very aware of. The older LightWave subpatches work linearly, while CC works exponentially.

To better illustrate this, the number of new polygons that a subpatch will be subdivided into is n*n for LW subpatches and 4^n for CCs. This means that for a level of 4, a single subpatch will be dived into 4*4 polygons (the level number is how many polygons a side will be subdivided into), for a total of 16 polygons. FOr CCs, it will be 4^4, or 4*4*4*4, which is 256 polygons. A level of 6 will result in 6*6 or 36 polygons for LW-SubDs, and 4^6 or 4096 polygons. CCs set to a level of 2 will give the same number of polygons as a level of 4 for the LW-SubDs. You can see this in Modeler yourself by creating a simple box, setting the SubD/CC levels in the Options panel and then freezing the object after converting it to either subpatch type.

In Layout, subdivision surfaces are also tripled, which will actually double the number of polygons, but the point count will not change because of this. This also assumes a patch is four sided. For LW-SubDs, you'd get the same number whether a patch is three or four sided. With CCs, the number is modified by 25% per each additional side. A three sided patch at level will have 25% fewer polygons - 192. A five sided one will have an additional 25%, for 320 polygons. Seven sides, having three additional sides would have 75% more polygons, for 448 polygons. And so on...

Because of this, you really need to be aware of what type of subdivision is set up on the model, because a value that works well for LW SubDs can quickly create more polygons than your memory can hold with CCs.

Now the interesting quirk (isn't there always one?)...

If you're using Pixels Per Polygons in APS, the number of polygons generated by CCs will actually be lower than the number generated by LW's SubDs. I expected this to be the other way around, but it's significantly lower. On a simple test, I discovered that on a model that has 1256 polygons, set to 5 Pixels Per Polygon, LW subDs would generate 1,439,852 polygons, while the same geometry, in the same scene, would only generate 183,360 polygons - approximately 1/8th the number that LW patches created with the same settings! I expected the numbers to be the other way around, if not nearly the same.

My only guess is that the CC algorithm allows for more more efficient variation in patching density across a patch than the LW method.

He Who Could Have Had Better Math Grades If He Knew Then What He Knows Now.

08-11-2006, 08:27 AM
I thought my CCs were weighing in a bit chubby. Cheers for that Dave!

08-19-2006, 09:09 AM
I thought it was just me. I get not enough memory dialog then I get it's setting it to level 1 or treating it as faces. Sometimes I get this message as I'm changing subpatch levels before I render. So what's better CC or Subpatch? I have a 1GB of memory and I'm maxed out. Is this is a bug or a hardware problem? Also it seems when I get over 3 million polygons is when I get these messages.

Thomas M.
08-30-2006, 10:50 AM
Running into the same problems here with a 90.000 poly object. Can't load this stuff as a SubD object without the memory error chain and a lot of pop-up windows, telling me what LW can't do.

Is there a workaround? I know from experience that LW is really picky about rendering stuff (memeory errors), so the "Can't load" problem could have been addressed by now. Anyway, how long do they let us wait for the next release, addressing bugs and not giving us any new features? During open beta we got up to 3 versions a week. And now not one in a month! They shouldn't have gone gold, because now it looks ridiculous to present 9.0.1, 9.0.2, 9.0.3 ... and so on to the public.


08-30-2006, 11:05 AM
You could model it a lower CC level and then heighten it during rendering time in Layout.

08-30-2006, 11:28 AM
I've been rendering 2.xxmillion poly stuff lately, with deformation, and as long as I don't get crazy with the numbers, I get renders without errors. This is with subd items. CC objects ... I've not gone back to because I can't get to grips with how quickly I can crash layout.

Thomas, what's your object? At 90k polys, my curiosity is high. According to Dave's math (and I should have paid attention in math classes, too), your object will only hit 270k with a subpatch level of 3 so it doesn't make sense that it won't load.
However, if they are ccs, the sizes would be ... much larger. ;O (After the first multiplication, cc at subpatch level of 3:90k*90k*90k, it was at 8100000000. Pretty clear that such numbers are prohibitive in most 3d apps.

This cc thing is gonna take some re-training.