Using lights for generating shadows only

[cire]

hi there! Is it possible in maya to create lights for generating shadows only? For example, I have this keylight which i disabled the shadow. Now i duplicate this keylight. This copy I then use for generating the shadows of the keylight. The reason I need this is because im working on a scene right now in which the keylight is very far from the character and the camera is positioned close to the character. So now, i'm getting all these flickering problems in the shadow plus i'm not getting nice contact shadows in the character. So i tried duplicating the keylight, then moving it close to the character. I disabled the depthmap shadows on the keylight. On the duplicate light, I enabled depthmap shadows and so that it wont affect the lighting on the character, i unchecked the emit diffuse and emit specular buttons. But this setup doesn't work. Is there a way that the duplicate light will only emit shadows and not light? I'm thinking of just doing it in comp but i just want to know if it can be done in maya or if somebody has figured out a way or workaround to this.

eric

[failure]

Use render passes.

[aaron_johnson]

use a shadow pass. one method is to assign everything a custom white shader (and set camera background to white), render lights together or seperately with shadows, and you'll be able to use a Multiply composite in post to overlay the shadow pass. this way you get to change the colour and opacity of your shadows in post too don't recommend the useBackground shader.

[cire]

well i've already figured it out. Same as what you said. I just used a white lambert shader whose color i set to a white value of 3. Also i increased incandescence to around 0.5 to remove any shading on non-shadowed areas. Thanks guys.

[joojaa]

It is actualy possible to do this without renderpasses by connecting the lights you want to a lightarray of a background shader and pluck the alpha out of that and multiply it with yoour shaders output and piping taht to surface shader taht you assing yto your surfaces. then unlink those lights from all objects.

Also you can make a depthmap shadowing light thats 0.001 intesnsity with a shadow color of -1000 in intensity. Thisway the light impacts the scene almost nothing at all but generates still a intense shadow.

Easy, huh?

[cire]

i just have a question with using a white shader. Is there a way that i can only capture the shadow information in the white shader. What I mean is that if the area is not in shadow, it is just white; no shading based on area's orientation with respect to the light. The reason being the shadow pass tend to darken the image when multiplied in comp. Areas of an object that is dark due to its orientation to the light source and not due to occlusion and which ideally should not be affected because its not in shadow becomes more dark since the corresponding areas in the shadow pass is also dark. Right now i'm trying to use the surface shader since its the ideal candidate being that it doesnt compute any shading. But i cant make it work. I tried connecting the lambert outColor to the surface shader color to no avail. What i want is to pipe the shadow information being computed by the lambert shader to the surface shader. So the surface shader will only darken areas in shadow and the rest is white. Any of you guys has any idea how to make this work? Maybe access the depthmap calculations being done by maya and redirect it somewhere else? I know that there is a way to this. Ideas, anyone?

[joojaa]

use background with a white background only catches shadows no shading info... But the shading info is meant to be mixed with a pure color render thats not shaded at all.

[cire]

do you mean to say that i render a colorpass without any shading? How do i do that in maya?

[aaron_johnson]

there was another method i used ages ago but can't quite remember how good the results were - try using a lightInfo node (i think the light's wolrdMatrix was connected to the info nodes worldMatrix, sampleDistance was connected to... something.... lol).

the other method worked quite well for me but i had to increase the diffuse of the shader material beyond 1, to about 1.25 i think. u are correct that obviously any area in the shadow pass that isn't white will darken a multiply composite, but i usually only set the post opacity to around 70-80% anyway so the effect is less notiecable.

[joojaa]

offcourse you can render as diverse passes as you like as long as you device your passes using mel you can prettymuch do anything you wish.

I mean i regulary reder out following passes:

Unshaded color, just shadow (no shading), just shading (on grey materials on one channel usualy i get the cam uv to the rest of the free channels), just occlusion, just specular, just reflection, camera normal, just fog, just selected lights, just frozen local cords, bump value, incadascence, overcolor (for those blooms), overcolor blur....

[joojaa]

now for the poweruser trick...

unpack and run the bat file. Se what happens oooh its magic...

renderingPassesDemo.zip

should be interesting to see who asks the first questiona about this

Ps oh and a quick fix as the original didnt work in folders with spaces easy enough to fix with quotes (didnt realy think of this).

[cire]

unfortunately, i dont have maya6.

If you dont mind me asking, how do you render out an unshaded color pass in the maya render? I tried adjusting the ambient values and the incandescence but i dont like the look im getting. The colors seem washed out. Also you mentioned an unshaded, shadows-only render pass. How are you able to do that? that's precisely what i need right now. any ideas on how to do that? please!!!

[joojaa]

what version of maya do you have then?

I use a bacground shader in conjunction with a whte background.

[cire]

thaaaank you! that is so wickedly simple never crossed my mind.
anyway im using maya5 right now.

thanks again!

[dezfx]

As a matter of fact, I just wrote a script to generate a "Shadow Only" spot light. You can download it here in the MEL Scripts area. The file name is "mh_shadowSpot".