View Full Version : faking diamond/gem reflections

08-11-2011, 12:09 PM
Hey all,

What would be the best way to fake gem-like reflections for a low poly game mesh where I don't have the ability to use a custom shader for it? Is there any way you can think of to do something clever with the diff/normals/spec to achieve that look?

I want to add some gems/trinkets to a character I'm working on but I'm having trouble figuring out how to really achieve those gem-like reflections. Thanks!

08-11-2011, 12:16 PM
How limited are we talking about? As in only using the standard Max renderer type restriction?

Setting up a fake cubemap into your Spec color map could help in theory, but if you could expand on how limited you are, and what kind of diamond/gems you're trying to achieve as reference, we can help you better. Also, can you add planes to the mesh? Some foggy LooAt camera planes will add alot.

However, for now, fake cubemap in Spec, some planes facing towards the camera around the diamond to fake 'twinkle' effect, and some opacity around the 'flatter' faces as opposed to the edged which won't have any opacity (or vice versa pending on material you try to achieve) to fake transulency.

08-11-2011, 12:22 PM
Incredibly limited.. Diffuse/spec intensity/spec color/normals. And opacity.

Can you expand on how to go about faking the cube map?

And the gems I'm looking to imitate would be like sapphire, ruby, aquamarine, etc.

Also, I could add planes to the mesh, I don't know how to make them "lookat camera" planes though. :/

08-11-2011, 12:47 PM
Pictures of what kind of effect you're looking for would be helpful

08-11-2011, 12:57 PM
Gems (http://celtathens.files.wordpress.com/2010/10/gems1.jpg)

Something like that. Just some very simple gems, no specific cuts or shapes.

08-11-2011, 01:10 PM
Most of the heavy lifting looks like it will need to be done with the geometry and normals map on extreme values, I'm not sure, but maybe you can get something fancy if you full invert your normal map and apply that, but it could work or not work, especially if opacity is involved. Try it.

Hmm, as for Spec Color,, you could take a map which belongs to your enviroment (or something close to it in hue, turbulance, etc) and put it in your Spec Color. I suggest warping the enviromental map on your model (In 3ds Max, you can use Render to Texture or Bake to Texture to warp a map without seams around your mesh, and export that map to use it as you spec color). Tint it with your gems color on lighter levels.

Spec Level and Gloss will need to work together, just add some Spec scratches in the level to add faint details to it and break the montonity, and Gloss needs to dependant on faces, leaving it one tone, but if you don't have access to gloss, playing around enough with the Spec Level should get you what you want.

Camera planes, it depends, what software are you using? Also, are double sided materials accepted?

08-11-2011, 02:18 PM
yeah, that's pretty straight forward. Facets in the normal, dark diffuse, high spec values.

I see a lot of people ask how to do certain materials... but all materials are done the same way when you've can't modify the shader.

Is the diffuse dark in the real world material? Then make it dark in your CG material.
Is the highlights/reflections strong in the real world material? Then make them so in the CG material.

Since you can use opacity you can build a bunch of polies inside the mesh to get the multi-layered look. Again you just copy what you see in the refs.

08-11-2011, 02:59 PM
It also depends on the amount of geo you're allowed to use, and render size. Are we looking at 1000 triangles or 10.000? And how many/bow big will the gems be in relation to the char. I take it you're not at liberty to post concept art, but a description should be okay (ask first, though).

08-11-2011, 06:57 PM
What platform is your target. With a cube map you could do a lot even without a fancy shader.

08-12-2011, 01:27 PM
Has anyone done this nicely in realtime? How do folks approach the refraction

08-12-2011, 01:59 PM
Has anyone done this nicely in realtime? How do folks approach the refraction

You can make most anything look great with a basic shader. If it doesn't look good, that artist should practice basic techniques more, rather than request fancy shader techniques and so on. In this case we're just talking about some small gems on a character.

For OP: Make a test, post it, let us see what you've got. Then it's easier to give feedback on what you could improve.