Revolving lights using radiosity (LW)

SebastianP

One of the stumbling blocks I've had with my newbie project was not knowing at the outset that there were limits to how many lights and objects that the Lightwave scene editor could handle - something that becomes a severe pain when you really need all those lights. A firend of mine introduced me to radiosity, and after reading up on it, I spent most of yesterday trying to come up with the correct settings to light the ship that way instead - not just skydome lighting and glowing beams, but flourescent tubes and floodlights that actually cast real light.

Now, while this works pretty well for static lights (if you turn up the luminosity of your surfaces far enough - I use between 2k and 10k % luminosity on my 40 mm diameter tube lights to get them bright enough, while the several meters wide beams from the secondary guns only need 1k %), what about revolving lights? Well, there are several methods available - 1) use regular lights and set them spinning: 2) make a radiosity source and set *it* spinning... both of these have the big drawback of using up finite resources, and they do clutter up the scene editor window something fierce. But wait, there's a third option: see that little E button next to the Radiosity box? Yes, that means you can vary your Radiosity over time. Presto *blinking* light. Not quite what we wanted, but we can expand on it...

To make a rotating light that's actually a static part of the model, start out by determining how fast your light is supposed to spin. Create a round object (a sphere or a disc), with a number of "sides" equal to the rotational period of the light measured in frames - i.e. for 1 revolution per second, use 30 sides, etc.

Select one of the sides, and assign it a new surface - name it something like "rotating light 1 of n") where n is the number of frames it'll take to go full circle. Open the surface editor, and make the light white (you can vary the color later by putting it inside a colored translucent box), then click on the E next to Luminosity. Set a keyframe at 0, with a value of 0% - this means the light is off at that point. At one quarter of your rotation, make a new key, and set it to whatever luminosity value you want for your light - higher makes more light, so don't be afraid to set the value to "awesome". At half-time, make a new key, and set it to 0, and at full time, make a third key and set it too to 0. Notice the graph swinging downwards? Negatives count as zero, so it doesn't matter much. Set the pre- and post-behaviors to "repeat, and the graph won't quite look like a sine, but close enough in the part we want (above 0). Close the graph editor, the right click on the surface name in the list and click copy.

Now, it turns out that cloning a surface isn't the most straight forward process, so your next task is to select the polygons to one side of the previous ones, and create a surface named "rotating light 02/n". In the surface editor right-click the name of the new surface and click paste - now you have a clone of the first surface. Click the E, and your graph will be there. Select all the keys, and move them one frame forward. Now, repeat the instructions in this paragraph until you're done with "rotating light n/n".

Now, go over to Layout, point a camera at your revolving light, turn on radiosity with some decent settings (I recommend going with a low ray count for this, and probably interpolation too), set your camera resolution to "painfully low"; and set the scene length to one rotational period of your light. Oh yes, the part I always forget (though the program does remind you), specify an output file. Finally, press F10, and go to bed. Some time after lunch the next day, when the scene has rendered (radiosity is slooooooow, if you want it to look good), you should be able to watch a clip of your non-moving, non-lightsource revolving light.

Oh, you want screen caps or a video clip? Give me about a week for the scene to finish rendering, please! :-)


SP

today

Just thought I'd point out that you can alter your LW config file so that your maximum number of allowed lights is something ridiculous like 10000000000000, that way you never have to be told that you are trying to add too many lights, same thing applies to the max number of objects in a scene:)

SebastianP

I don't know whether to kiss your feet or bash your skull in, you know that right? For three weeks I've been thinking that the best I'd be able to do was a mostly static model, with things such as airlock doors being of very low probability of ever moving.

To heck with all of that. From now on, if it's supposed to be movable, it will EFFING well MOVE, down to the last access hatch!

Time to start afresh folks.... RAWR!

SP

vfxart

Having quickly read over your post... you are throwing far too much at LW, and it's not the program that's in error. Your scenes sound way too bloated. Radiosity is nice, but is a poor choice for a lot of what people try to use it for. Careful lighting can get you comparable results, and viewing your final output, no one will pick up on the difference. It sounds as if you can use nulls to control a lot fewer lights, though your explanation isn't quite clear on the effect you're trying to achieve. Also, LW uses negative lights, so don't assume that negative counts as zero. Last, most artists I know use little more than spotlights, and get incredible results out of them. Maybe an occasional distant, maybe an area or a few points, but mostly spots.