New technique better than parralax mapping

Graphics and GPU Programming Programming OpenGL

Started by Bender77 October 11, 2004 05:50 AM

16 comments, last by EvilDecl81 19 years, 6 months ago

1,826

October 11, 2004 04:02 PM

Quote:Original post by sBibi
superpig> this one does produce correct silhouettes, not like parallax mapping, it's just that these screenshots don't show it.

the bumps don't stick out of the surface, but dig inside it.
if the pixels that connect the quad edges to the rest are rendered transparently, you get proper silhouettes. (your meshes faces need to be pushed along their normals so they enclose the highest possible bump).

Ah. Does it work if bumps touch the edges of the quad?

Richard "Superpig" Fine - saving pigs from untimely fates - Microsoft DirectX MVP 2006/2007/2008/2009
"Shaders are not meant to do everything. Of course you can try to use it for everything, but it's like playing football using cabbage." - MickeyMouse

sBibi

241

October 11, 2004 05:44 PM

what do you mean?
the only problem there is with silhouettes (but you can't do anything about this with a flat quad anyway, is that the closest edges of the quad will seem to "cut" the bumps that go inside the quad, and will make the quad appear as more or less a window that lets see what's underneath.

but for polygons connected into a complete mesh that represents a closed volume, you won't get this problem (I'm not 100% sure, I didn't test any of it, but I really don't see why it wouldn't work, there's no reason at all... and you can get the silhouette of the object to look bumpy like it should be if you use alpha test and set the alpha value of all boundary pixels that don't touch the virtually displaced mesh to 0.

however, there might be (and probably are) some artifacts with sharp surfaces, where bumps stick out the opposing surface, and at the edge between two faces that have a high angle relative to each other. hmm, did that sentence sound english? :D. sorry, I'm having trouble saying what I'd like to say :/
anyway... there aren't any flattening of the bumps anywhere on the surface, they stay consistent, and you can get proper silhouettes :)
but a demo showing this would be cool...

Anonymous

October 12, 2004 05:04 AM

Quote:Original post by sBibi
but for polygons connected into a complete mesh that represents a closed volume, you won't get this problem (I'm not 100% sure, I didn't test any of it, but I really don't see why it wouldn't work, there's no reason at all... and you can get the silhouette of the object to look bumpy like it should be if you use alpha test and set the alpha value of all boundary pixels that don't touch the virtually displaced mesh to 0.

For polygons in a complete mesh, there is no problem if a bump from one triangle comes into the area corresponding to another triangle. The above screenshot with the quad is proof of it as the quad is actually two triangles. The problem is at triangle edges but only those edges which are at the object's silhouette. For the rest of triangles the neighbouring triangles will handle the "spilled" bumps.

I don't think setting alpha to 0 and then using alpha test will solve it because if it works at the silhouette, it will break when both the tris sharing the edge in the silhouette are visible. More info needs to be stored.

sBibi

241

October 12, 2004 09:20 AM

Quote:For polygons in a complete mesh, there is no problem if a bump from one triangle comes into the area corresponding to another triangle. The above screenshot with the quad is proof of it as the quad is actually two triangles. The problem is at triangle edges but only those edges which are at the object's silhouette. For the rest of triangles the neighbouring triangles will handle the "spilled" bumps.

mh yes, you're right, it should work if the face normals are interpolated for each fragment (and that'd be the case). then it works well for any mesh, except on the mesh screenspace boundaries as you said, but that's without alpha test.

Quote:I don't think setting alpha to 0 and then using alpha test will solve it because if it works at the silhouette, it will break when both the tris sharing the edge in the silhouette are visible. More info needs to be stored.

I think it would work pretty nicely, if you set to 0, as I said two posts above, only the pixels that don't fall into the virtually displaced mesh, and these pixels exist _only_ on the mesh silhouette, not when the two tris are visible, I mean, you won't have transparent pixels right in the middle of a surface between two connected faces, only on the silhouette.

Alura

174

October 12, 2004 02:17 PM

It's a nice new technique, but I wouldn't say better than parallax mapping, simply due to it's speed-looks relation, which is quite lower than parallax mapping (ok, it's prettier, but also a lot slower).

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sBibi

241

October 13, 2004 06:30 PM

superpig> OK, forget what I said about silhouettes, I understood the algorithm the wrong way, and when you think about it, it seems obvious... a pixel shader can't know how the surface it belongs to will evolve, and the shader assumes the surface follows the surface tangent at the pixel location, and this introduces some deformations on the silhouettes (although much much better than parallax mapping), I should have read the shader code... sorry about that :/

EvilDecl81

360

October 13, 2004 07:35 PM

Quote:Original post by Bender77
Relief mapping :
Seen on opengl.org

In fact it's "simply" some raytracing into an heightmap using the pixel shader. You can even raytrace self-shadows (and local reflections I guess). It look awesome, but considering the high amount of pixel shader instructions needed ( Compared to parralax mapping in example ) I don't know if it's yet usable in some game engine ( Even on GeForce 6800 ).

Maybe the solution is to use this technique near the camera, and to use parralax or standard bump-mapping instead farther. The problem will be to smoothly transition between these LODs (especially between relief mapping and others)

The best paper I've seen on these kinds of techniques is this one (published in GI 2004). The key reasoning in this paper was to break the interesction prisms into 4 tetrahedrins, which makes doing intersections mathmatically cheap. This paper was implemented on a Radeon 9700, IIRC.

http://www.gris.uni-tuebingen.de/publics/paper/Hirche-2004-Hardware.pdf

EvilDecl81

360

October 13, 2004 07:36 PM

Quote:Original post by EvilDecl81
Quote:Original post by Bender77
Relief mapping :
Seen on opengl.org

In fact it's "simply" some raytracing into an heightmap using the pixel shader. You can even raytrace self-shadows (and local reflections I guess). It look awesome, but considering the high amount of pixel shader instructions needed ( Compared to parralax mapping in example ) I don't know if it's yet usable in some game engine ( Even on GeForce 6800 ).

Maybe the solution is to use this technique near the camera, and to use parralax or standard bump-mapping instead farther. The problem will be to smoothly transition between these LODs (especially between relief mapping and others)

The best paper I've seen on these kinds of techniques is this one (published in GI 2004). The key reasoning in this paper was to break the interesction prisms into 4 tetrahedrins, which makes doing intersections mathmatically cheap. This paper was implemented on a Radeon 9700, IIRC. It is quite feasable on next-gen hardware.

http://www.gris.uni-tuebingen.de/publics/paper/Hirche-2004-Hardware.pdf

EvilDecl81

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