Light objects

[thrasherstudios77]

Aloha

I was messing about with lights and realized that Houdini doesn't have presets for different types of lights, that you would usually find in anohter 3D app. What I mean is there is no Directional light, or point light, or area lights, seems Houdini starts you off with a spot and then gives you different settings to alter that light, which is fine. However I am not sure how to utilize those settings to get the different light types.

Could someone give me the run down on making:

Directional light- shines light evenly in one direction, like the sun or moon would cast light

point light- shines light in all directions from the source of the light, like a incadencent light bulb

Area light- used to simulate the rectangular reflections of windows on surfaces, basically is a rectangular light that casts light in a rectangular shape.

Thanks in advance

Ben

[AndrewVK]

Directional - standart light "Projection - orthographic"

Point - standart light "Cone - Off"

Area - custom VEX shader

[danteA]

You can also make a light array to simulate area lights.

[plan9]

You can also make a light array to simulate area lights.

...then you can *export type* and install the optype so it loads everytime!

[thrasherstudios77]

Thank you for the replies, every thing makes sense except the area light.

Could you explain how to make an area light out of a Vex network or through a light array.

Ben

[Stremik]

How about... Is it possible to make an object to emit light?

[stu]

Short answer - no, there isn't a way to have an object emit light (yet), but here's a way you can do it:

1. Make an object that you want to emit light (duh) with points that are fairly evenly spaced.

2. Make a light that will be the guide for how bright the light being emitted will be, and give it's translation values the following expression:

point("/obj/emitter_object/end_sop/",0,"P",0)

The "emitter_object/end_sop" is the last sop in the object that is going to emit light, the first "0" is the point that the light is going to be copied to, the "P" means point (leave it) and the last "0" means the "x" position, so in the "ty" field in the light, the number would be "1", and for "tz", it would be "2".

Now, copy and paste the light, and channel reference it's colour and dimmer values to the first light's values so that you only have to change one light to affect them all. In this light, change the first "0" to "1", because this light is being copied to point "1" in the object. Now, copy and paste this light so as to occupy the remaining points in the emitter object being sure to change the first number in the expression to the next point number each time.

Make sure to angle the lights in the right direction so that light is pointing away from the object at the appropriate angles, and yer done. (there's probably an automatic way to do this, but I'm too lazy to figure it out )

I made it seem way more complicated than it is, and if you want shadows (you probably do) remember that the more lights you have, the longer the renders will take.

stu

[AndrewVK]

A primitive example of VEX rectangle area light.

....too slow when shadows turned On.

rectarealight.zip

[pockets]

Raytraced shadows might be too slow for most applications of the light array method for soft, diffused illumination BUT Houdini/Mantra is very fast at generating shadow maps. Faster, in my experience, than Renderman.

Even back in the 4.05/4.1 days I was able to create arrays of a hundred or more point lights and blow through the shadow map process in a matter of minutes on what would be ancient hardware by today's standards (450-500MHz PIII based SGI 320). Your shadow map resolution doesn't have to be high since you'll want all these shadowmaps to softly blend together in the final render.

You'll want to have scripts that go in and turn autogen off/on and to change the string for your shadowmap path, etc., and possibly to swap shaders. Even for a small array of nine or so lights this can be a real pain to do by hand.

Until H6 it's still a practical way of achieving realistic lighting for applications where diffuse interreflection or specular-to-diffuse reflection isn't an absolute must.