Game "refractions" without Ray Tracing?

[slapnutz]

How do games archieve refraction effects without using actual Ray Tracing for features such as glass or water?

Is it faked or just as accurate as say using RT in maya/max/mental ray.....etc

 

[Arwin]

I don't know much about these things, but I'm fairly sure most of the time they are faked by shaders.

Considering the board we are on though, if you mention specific titles I think you'll be able to get really specific answers on how the effect was achieved in that particular game.

 

[MDolenc]

That would usually be accomplished with render to texture operations these days.

 

[slapnutz]

I don't know much about these things, but I'm fairly sure most of the time they are faked by shaders.

Considering the board we are on though, if you mention specific titles I think you'll be able to get really specific answers on how the effect was achieved in that particular game.

Glass in Call or Juarez and HL2: Ep2. Water in Crysis.

 

[Davros]

theres a refraction effect in quake 3 (source is available)

 

[Rodéric]

(Considering water here)
It's basically rendering reflection & refraction textures, then in the pixel shader compute Fresnel, use the Normal Map.

As an example see ATi's nature demo
http://developer.amd.com/documentation/videos/pages/ATIRadeon8000SeriesDemos.aspx#ati

 

[Humus]

The easiest way to make refractions is simply to copy the backbuffer to a texture, then render your glass or water using that texture perturbing the texture coordinates slightly using a normal map.

 

[Anteru]

Glass in Call or Juarez and HL2: Ep2. Water in Crysis.

For Half-Life 2, take a look at this presentation: http://www2.ati.com/developer/gdc/D3DTutorial10_Half-Life2_Shading.pdf

Around page 87, you even get the source code for their refaction effect, which is - like Humus already said - just a peturbed texture lookup.