View Full Version : LW can't render multy point poly

Boris Goreta
02-13-2010, 11:16 AM
LW 9.6 can't render this object properly but displays it OK in the OpenGL and FPrime renders it correctly. What is the problem here ? And no I don't want to triple it. :o)

02-13-2010, 12:05 PM
probably some NonPlanar breaking in there. is there a reason it has to be more than 4 points?

- Will.

Boris Goreta
02-13-2010, 12:12 PM
Is there a command to make it planar ?

02-13-2010, 01:33 PM
Is there a command to make it planar ?

Triangulate, because triangles are always planar.

But in your case, your polygon probably has 5 or more points. Check out Polygon Statistics window 'w' short-cut and Merge/Weld Points.
Probably your 1st and 2nd, or 1st and last points are at same locations (renderers use 1st, 2nd and last polygon's points to calculate normal vector-, if point position is same, normal vector will be incorrect, and ray will never hit polygon while traveling kd-tree in scene graph).

02-13-2010, 02:58 PM
There's a way to make sure a polygon is planar. Use a plugin called Cplane.

I used it on the surface that was having problems and now renders just fine.
Looks like calssic camera renders fine anyway. But notice how the normal (grey value) is a bit different after it's planar.


Basicly you try to make that polygon sitting on the floor the best you can and then Set Value to 0 = Planar. If you use triple on a highly non-planar poly you can end up with faceting render.

This is also great when you want to make sure many points belong to the same plane even if they are not in the same polygon; Example: Edge Loops of an head model.
It would be great if LWtools like Stretch could pick a poly's normal to define the axis. That would be faster than using a construction plane.



02-13-2010, 03:16 PM
Classic camera is using scan-line algorithm to check what is visible from camera- that's why polygons not visible in perspective camera, are renderable in classic camera. In scan-line all polygon's points are converted from world 3d to screen 2d coordinate space in pre-processing, then filling buffers in 2d space, without using polygon's normal vector for calculations.

This only workaround directly visible from camera polygons- if such broken poly is seen from reflection, refraction or other ray-tracing routine, it will suffer the same as in perspective camera. Therefore it's needed to get right of bad polygon regardless of used camera.

02-13-2010, 03:21 PM
There's a way to make sure a polygon is planar. Use a plugin called Cplane.

Great insights there! Thanks alot for the tip!!!


Boris Goreta
02-13-2010, 03:43 PM
Thank you for explaining everybody, I will try that CPLane plugin. Thanks !

02-13-2010, 07:29 PM
An example of making an edge loop planar, sometimes usefull, when you tweak a model a lot, but after you want to stick to something more straight along the loop



03-17-2010, 04:54 PM
Seems that http://www.lwplugindb.com/Plugin.aspx?id=20e5fbf4 does a fine job correcting these without the cplane fuss.


EDIT:Rofl, it seems that if the poly is actually planar but the normal is messed up, all you need to correct the normal is to triple and merge those triangle back into the poly and it will correct it... Try that in you model Boris.