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Hulag

OpenGL Reflections and refractions.

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I would like to add support for reflective and refractive objects in my engine. Now, all the stuff I have seen related to reflective oceans and stuff like that but that's easy since its a single plane always pointing in the same direction. What I want is something similar to If you want to see that running download this video (14MB). BTW, I use OpenGL, glSlang for shaders, and I don't have FBO yet but I will very soon.

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You can find some source code and binaries right here.
You can take off the chromatic aberration by refracting your view vector only once and using all of its channels in the final mix.

[Edited by - JavaCoolDude on June 30, 2005 9:15:43 PM]

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Original post by JavaCoolDude
You can find some source code and binaries right here.
You can take off the chromatic aberration by refracting your view vector only once and using all of its channels in the final mix.

But how does this method work when the shape of the mesh its so different from the shape of a cubemap. For example in the screenshot I posted there are a bunch of reflective and refractive walls which given their shape it wouldn't fit a cubemap so well, how does it deal with that? and from what point should I make the cubemap in that kind of shape?

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u dont need a cubemap for the above image, the refractions are only little.
just grab the background behind the "glassbox" and use that as a lookup with the normals providing the distortion

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Original post by zedzeek
u dont need a cubemap for the above image, the refractions are only little.
just grab the background behind the "glassbox" and use that as a lookup with the normals providing the distortion

What if the index of reflaction is such that you need to refract to a place that isn't within the view frustum?
Also, what about reflections in those kinds of situations?

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Original post by Hulag
Quote:
Original post by zedzeek
u dont need a cubemap for the above image, the refractions are only little.
just grab the background behind the "glassbox" and use that as a lookup with the normals providing the distortion

What if the index of reflaction is such that you need to refract to a place that isn't within the view frustum?
Also, what about reflections in those kinds of situations?


It seems like ugly hack to do it this way, but this is how it's usually done (since ray-tracing is still far from real-time usage).
You just draw the cubemap from the center of the reflecting/refracting object, with camera that has the same orientation as the object. So it's done in it's local space. Then when you need to render the object, you transform the eye-to-object vector to that object's space and calculate the reflectance and refracting vectors with that to look up in the cubemap.
Whole lotta rendering to do for lots of reflecting objects :(

ch.

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What if the index of reflaction is such that you need to refract to a place that isn't within the view frustum?
Also, what about reflections in those kinds of situations?

move the camera :) im not joking
for reflections though youre better served with a cubemap, though in the abovescreenshot there r no reflections

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Original post by zedzeek
Quote:
What if the index of reflaction is such that you need to refract to a place that isn't within the view frustum?
Also, what about reflections in those kinds of situations?

move the camera :) im not joking
for reflections though youre better served with a cubemap, though in the abovescreenshot there r no reflections

The floor is reflective, and the wall on the right of the 4 cubes thing is also reflective.
Now, the problem I see with cubemaps is reflecting local object, to test that I took JavaCoolDude's example, and replaced the sphere with a big plane and no reflections from the particles showed up, and the refractions where wrong.

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Cubemaps are not good for local reflections. They're good when the reflected objects are supposed to be infinately far away(like a skybox). It can also work to render reflections on small, "closed" objects, but with planes it doesn't work so well.

What you see in the screenshot are just planar reflections and refractions. They get rendered into a texture, and then that texture is projected into the geometry with the texcoords slightly distorted using a normalmap. Not physically correct, but it achieves the desired effect.

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