PDA

View Full Version : object cast shadows


wassie
04-17-2006, 11:19 AM
is it possible to let an object cast shadows?
lets say i make a plane, and give it like a white glow that it looks like a lamp.
it it then possible to let it cast shadows?

ImUrPeTii
04-17-2006, 01:40 PM
Maybe u can draw some pics out so the others could catch ur idea.

wassie
04-17-2006, 02:31 PM
oke,
lets say you have this basic composition:
http://img128.imageshack.us/img128/4196/12pz.th.jpg (http://img128.imageshack.us/my.php?image=12pz.jpg)
-you have a plane as a ground
-a simple ball
-and a plane above it (its white but i made it yellow else you couldn't see it)

now what you do is:
http://img101.imageshack.us/img101/1152/22sn.th.jpg (http://img101.imageshack.us/my.php?image=22sn.jpg)
you give the plane (the yellow one):
-diffuse a output
-and oppasity a fallof (so it will look as a light with a bit of volume)

as you see there is an reflection on the ball, because of the plane,
so you would think it is a light. but there are nog shadows!

how can i make it like this:
http://img222.imageshack.us/img222/9088/32ry.th.jpg (http://img222.imageshack.us/my.php?image=32ry.jpg)

with a shadow?

wassie
04-17-2006, 02:53 PM
made some renders for ya,
here is the composition (with the reflection):
http://img222.imageshack.us/img222/9471/11ej.th.jpg (http://img222.imageshack.us/my.php?image=11ej.jpg)

and i want it like this:
http://img71.imageshack.us/img71/6062/22wt1.th.jpg (http://img71.imageshack.us/my.php?image=22wt1.jpg)

(i just put a omni behind the plane)(the shadows aren't right, cause it must be allot smaller, but you get the idea)

jeremybirn
04-17-2006, 04:42 PM
In that case an area light would be the best way to render the shadows, but if you had more complex object shapes, then yes you can have the objects illuminate other objects and shadows will appear under the sphere from that.

Take the scene you've got, turn the brightness of the light down to 0, make the white plane's incandescence or ambient color very high (so it stays bright even without light) and render in MR with Final Gathering turned on. The white object will light the sphere and cast a shadow where appropropriate. You make need to crank up the incandescence on the surface or the final gather scale in render settings in order to make it bright enough to see.

Full GI with photons would also allow bright objects to illuminate and shadow other objects. The "shadows" you see aren't strictly defined as shadows to the renderer, they are an occlusion effect that's a natural part of the global illumination algorithm, but visually and in terms of their phsysical placement they are shadows.

-jeremy

wassie
04-18-2006, 11:43 AM
thanks man!
but you are talking a bit to advanced for me,
can you maybe explain where i can find "incandescence"?

and with "turn the brightness of the light down to 0"
do you mean the omni light i allready have or the whole scene or something?

jeremybirn
04-19-2006, 05:58 AM
thanks man!
but you are talking a bit to advanced for me,
can you maybe explain where i can find "incandescence"?

and with "turn the brightness of the light down to 0"
do you mean the omni light i allready have or the whole scene or something?

If you want to do something simpler, just use an area light with raytraced shadows, instead of all the global illumination stuff.

It sounds as if you're using 3D Studio Max, so I think you have ambient color and "self illuminaiton" as the material options that will make the surface bright even when no light hits it.

You can turn the omni's multiplier down to 0 if you don't want it to emit any light, so that all the light will come from the mental ray rendering with final gathering. (I suggested that instead of deleting the light because some software adds a default light for you if you have no lights in your scene when you render.)

-jeremy

CGTalk Moderation
04-19-2006, 05:58 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.