RAYTRACED SHADOWS AND FAKED CAUSTICS
A problem with the Scanline-Renderer that ships with the base package of MAX is: it can't do caustics. Caustics are are concentrations of light that appear with, for example, magnifying glasses when light shines through them. This is an extreme example, but a wineglass also casts these caustics, although a little weaker (the doesn't get bundled together as much as with the lens of a magnifying glass).
The shadows cast by a glass can also only be faked using tricks. MAX R3 contains many new features which make the task easier. It would be even easier with a radiosity-renderer, such as Mental Ray - currently the best solution. It costs a lot of money though.*¹Let's assume You've already modeled a glass. The glass is set on a table, and is being illuminated by a simple spotlight. Shadow casting has not been activated yet, and no materials have been applied so far. Your scene could look like the image above.
Let's start with the material for the glass: Open the Material Editor , select a material slot and apply the material to Your glass.
First of all You're going to assign a Raytracemap to the Refraction map channel. To do so, open the Maps Rollout, click on the Refraction map channel and select "Raytrace Map" from the newly opened dialog.
Then increase the shininess strength to 100 and the shininess to 45. Render an example image, it should look somewhat like the image to the left.
On to the lighting. Select the spotlight and check the box "Cast Shadows". Scroll to the "Shadow Parameters" rollout and change the shadow type to Raytraced Shadows. If You make a test render now, the glass will cast a shadow, but it is completely black. To fix this Your glass will need a transparency (opacity) added to it. The difference between refraction and opacity is that refraction only applies to bending light, whereas the actual transparency is determined by the opacity value. If You let the opacity of a material at 100, the object will not be transparent, i.e. it won't let any light rays through: the shadow remains black. If You change the opacity to 0, the material will be completely transparent, light rays pass through without losing strength. Note: The shadow will always remain black with shadow-mapped lights - they do not respect the transparency of a material.
Back to the Material Editor : Open the Maps Rollout of Your glass material again, and click on the unused Opacity map channel. Select "Falloff" in the newly opened dialog. Check the X-axis as the falloff direction in the "Falloff-Parameters" rollout. Render an image and compare Your result with the image to the right. By applying the Falloff map we have not only gotten transparency in our shadows, but also the base setup for our "Pseudo-Caustics". Now the shadows need to be brightened, as they are still to dark as they are now. To do so, select Your spotlight and go to the shadow parameters. Go to the Color swatch and give it a gray color at a 170 value. Then increase the density of the shadow to 2.
The result is shown in the middle image on the right.In the shadows cast by the light we now have Caustics, concentrations of light, even though not real ones. The shadow is, however, in some areas still too defined - You can clearly see the edge of the glass.To lessen this effect a little, copy (don't choose instance!) the spotlight and change the shadow type back to shadow map. You now have a raytraced- and shadow mapped-shadows light in the same spot. Change the color of the shadow back to black, and decrease the density to 0.6. Open the Shadow Map Parameters rollout and increase the sample range to 8. This will soften the shadow map's shadows. Now You have to play around a little: Because of the two spotlights in the same scene everything will, of course, be a little lighter. You can prevent this my lowering the multiply values (found in the General Parameters rollout) of both spotlights to about half their original. This, in turn, will affect the look of the shadows. So it's just a question of playing around with the values until You've found the look You want.
I myself have reduced the multiply values to 0.7. The result can be seen in the last image. Lastly I have added a little noise as a bump map to the material and added a raytrace map to the reflection map slot. The resultant scene can be downloaded here.
Notes from translator :
*¹ - The recently released Bunch of Volumes is a good and much cheaper alternative.
