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Cubemap generation

Started by pasman Feb 16, 2005 at 5:12 PM 5 replies 1.2k views

Original Post

Feb 16, 2005 at 5:12 PM

hi, I know this might be a stupid question but here goes... I want to add reflections to my scene, for now to the water. If I'm not mistaking this can be done using cubemaps and shaders. For their generation I have to render the scene 6 times, for each face of the cube. Is this approach common in games (I belive Morrowind uses this approach for water). Are there some things I need to know before starting implementing this (regarding performance) beside the fact that I don't need to generate them every frame. I'm using OpenGL and CG for shading. Should I use other methods for water reflection? Thank you.

poly-gone

Feb 17, 2005 at 10:42 AM

Since the reflections will be distorted, you can get away with a fairly small cubemap. Since it's generated almost every frame, this will help save some fillrate.

The best method for rendering water is by using planar reflection and refraction maps. There's an article here on GameDev by Yann that describes the technique in fair detail. You might want to check that.

pasman

Feb 17, 2005 at 4:27 PM

thanks, I know about the method you mentioned, but if I have the cubemap I could use it for all reflections...

Also, are there any games using this method, does it worth to implement (and to get good performance results) or should I stick to planar reflections?

pasman

Feb 18, 2005 at 3:16 PM

and one more thing...since I have tons of other things to do to the engine and the game itself, i'm looking for the fastest method to implement and also to give good results...so i thought cubemaps and shaders would be pretty fast to implement...any thoughts?

silvermace

Feb 18, 2005 at 5:06 PM

using 6 PBuffers that share their OpenGL names (wglShareLists) you should be able to render on each pbuffer with the camera @ current position and only changing the look at vector to up(0,1,0) left(1,0,0) etc etc.

once you've rendered the scene, using WGL_ARB_render_texture bind the appropriate PBuffer to the matching side of the cube-map, and hey-presto.

not too hard, just a paint to setup.

poly-gone

Feb 19, 2005 at 10:45 AM

Quote:
Also, are there any games using this method, does it worth to implement (and to get good performance results) or should I stick to planar reflections?

It depends. The planar reflection method for rendering water is pretty "texture" intensive, especially since you need atleast 2 fetches of a bump map, a reflection and refraction map and a couple of more textures depending upon the "detail" you want to achieve. Besides, the shading calculations are definately more complex than the general cube-map method. You might want to try both and see how things go.

pasman

Feb 20, 2005 at 7:42 AM

thanks, for start i think i'll go with the cubemap approach and see the results...anyway thank you all for the responses.

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