View Full Version : render 2x as fast!

08-17-2003, 06:56 AM
I recently read that everyone hates to wait for radiosity renders. And that the renderer is a bit outdated for Architectural work. Of course I agree. So here's a trick for you all to speed up your renders! I only just found out about it, so I didn't do much testing yet, only the scene I was currently working on. But it cut my render time in half with a scene taking about 3 mins to render, and I think it will cut the render time down even more with longer renders. I also think this is most useful for architectural scenes.

And best of all, the image is absolutely identical, pixel perfect, to the longer render.

Enough talk, let's get to the trick: http://www.funnyfarm.tv/thelab/rendertrick.htm

Have fun,

Wybren van Keulen
Funny Farm

08-17-2003, 07:17 AM
thanks wavk for posting your findings :)
always good stuff !!



08-17-2003, 08:07 AM

this is where newtek should implement lense deformation... not as a post effect.

did you use raytrace transparency?

08-17-2003, 08:09 AM
If you watch LW closely, you will notice that the decisive factor of when a poly is rendered, is the distance of the middle of the polygon to the camera (fairly standard Z-Buffering btw...).
Subdividing large polygons will reduce your render times as well in many cases.
As you've noticed, it pays off to watch LW render...


08-17-2003, 09:39 AM
nice tip! thank u!

Gui Lo
08-17-2003, 09:41 AM
What a simple idea.

I guess we have all seen this happen with transparent stuff but never went the extra step.

Thanks Wavk for sharing this.

08-17-2003, 09:46 AM
i havent spent much time playing with this trick. here are some questions
do you loose backdrop image and alpha channel?

08-17-2003, 10:37 AM
doesn't matter, just tell the poly in front of the cam to un-affect alpha

08-17-2003, 10:48 AM
When I rendered from the inside looking out a window, LightWave rendered all the unnecessary stuff, too! Like the glass plates on the other floors, which were sequentially totally covered by the walls.

I don't quite understand this, does that mean the other floors not viewable on the image were rendered as well ?

Anyway, does this trick speed up the rendering process only on radiosity scenes ?

I tried this trick on a simple scene, just a sphere on a ground with one spot light and AA off. Placing a 4 point polygon, normal facing to the camera with a surface of 0% diffuse, etc and 100% transparency, the rendering took twice as long ( 2.8 sec ) than rendering it without the transparent polygon ( 1.3 sec ).

The only thing I didn't do was parent the transparent polygon to the camera.

08-17-2003, 11:06 AM
This trick will only work on very complex scene, especially on scenes with large polygons (like walls, floors, etc...).

08-17-2003, 11:08 AM
great tips

it does speed up my rendering about 10%.

But sadly, this trick seem doesn't work with g2 surface, because all surface in my character behind this transparency polygon have g2 appied, I can't get my character's alpha channel show up.

anyway, look like I can use this tip with non g2 objects.


08-17-2003, 11:10 AM
Originally posted by Lightwolf
This trick will only work on very complex scene, especially on scenes with large polygons (like walls, floors, etc...).

thanks - will keep that in mind ;)

08-17-2003, 11:29 AM
Does the transparent object in front of the camera have to have thickness or can it just be a flat plane?

Do I have to have raytrace transparency turned on?

08-17-2003, 11:33 AM
I haven't checked it yet ( think subdividing will help just as much...) but:
Raytrace Transparencies on !
No thickness.

Basically this trick seems to force LW to raytrace the whole image, instead of using the Z-Buffer renderer for the first hit detection. This seems to only makes sense with scenes that use raytracing heavily...


08-17-2003, 12:03 PM
it didnt speed up my render at all, infact, it seemed to not let "shading noise reduction" to do what it does, so the radiosity looks awful, also all glow intensity in the scene appears to be eliminated.

08-17-2003, 12:13 PM
More likely your radiosity settings...

Great tip!

08-17-2003, 12:50 PM
I just read this, I'm going to render out a scene that I just created. I'll check to see what the fruits of the efforts are. I'm using an area light, one spot, and background radiosity.

08-17-2003, 12:59 PM
Whoa, so many responses in so little time! Great community (I'm new to LightWave:).

I indeed had no thickness to the polygon and I had raytrace transparency on like Lightwolf said. I'll also try subdividing the wall polygons and see what happens!

Yes, I only tried it with an architectural scene so far. Didn't try it with shading noise reduction, I used the interpolated version of gi.

Thanks for the responses,


08-17-2003, 01:28 PM
Lets just hope Newtek finally optimizes the renderer so it's not so slow.

08-17-2003, 01:45 PM
I gave it a try and it decreases my render speed (radiosity scene )very slightly ( 15mins instead of 16mins) but the noise is present even with "Shading Noise Reduction" turned on.

With non radiosity scene, it increases my render speed instead!

But it is fun and wierd to watch LW render from top to bottom like scanline renderer.:D

08-17-2003, 02:15 PM
I could be completely wrong but I'm pretty sure subdividing the outer glass windows in your office block would prevent most of it being rendered unnecessarily.

As I understand it, LW will render the whole polygon if even just a little bit is visible in the final render as Lightwolf (I think) pointed out. As the man said, it's basic Z-buffer poly culling.

08-17-2003, 02:42 PM
This kind of things only show LW rendering engine should be improved soon in order to be more efficient and smarter with different kinds of scenes, geometry, memory handling and surfaces.


08-17-2003, 02:43 PM
my system keeps crashing just before it starts to render. Not too sure why. I'll get back to you on this one...


08-17-2003, 04:24 PM
okay. now that I've managed to get this thing to work. I had a single plane 4-sided polygon with all the settings as suggested and I got this in 35 min. 26 sec.

Then this EXACTLY THE SAME scene in 31 min. 8 sec.

Now what happened with the colours and lightness of image I don't know, but the last image was the final output.

Go figure.


08-18-2003, 12:26 AM
Fabmedia, they are hypervoxels that render differently right? Seems a bit weird .. hypervoxels always have been though ...

08-18-2003, 01:54 AM
Hi fabmedia,

I put the two images on top of each other in Photoshop and noticed that the bump map of the wooden boards isn't anti aliased correctly in the fast version :( So I guess that can be added to the cons list. By the way, wickid test image, really like it!

And you're right, LightWolf, Subdividing helps LightWave to see what's on top, too! It does, however, mess up your mesh. I wouldn't want to continue modeling with such a mess-mesh.

However, if you select the mesh and Reduce Polygons with no removal, it's immediately cleaned up :) Thanks for the idea!


08-18-2003, 02:04 AM
Hi wavk,

you, it does mess up your mesh, on the other side, it can speed up just about any kind of render, even without raytracing etc..., and you can use "Shading Noise Reduction" without problems too.
Which shows how much potential LWs renderer has for improvement... (by the way, I'm using that technique since 1993 or so, back on the Amiga. I had a scnee with 20.000 polygons, a kid's room, with a reflective floor and a carpet on it. LW would always render the complete reflective floor and then the carpet on top. Once I subdivided both, LW got a bit smarter...).


08-18-2003, 09:49 AM

Thanks for the compliment. The final image is this...

It took a bit, but it's a portfolio peice. I'm quite indifferent to this method because I didn't really see a difference in speed. But I'm working on an image of my office right now, so I'll put it to the transparency test too. When I start posting the WIP I'll let you know.