Exploring Sphere Mapping and OpenGL Extensions in Computer Graphics

1. Christmas Break By Paul Zimmons

2. Anselmo’s Paper • Started from the Summer of 1999 • Destined to become a Tech Report • ~25 pages of just Sphere Maps • Conclusion: • “Sphere maps are cool but not that cool.”

3. OpenGL • Going through Advanced 97 codes, OpenGL extensions, and company demos • What can we use from these? • Apply to OFF

4. 1997 Course Notes Code • Many good things • Making sphere map out of 6 images (cube) • Although I later found another way • Short projective texture demo • Not sure how applicable (shadows?) • Sphere map light source • Want a sphere map highlight at a certain direction • But as soon as you move your head it goes all over

5. Projective Texture Example Projtex.c: Projective textures are hard to control.

6. Just draw a mesh sphere with an OpenGL light at the right place. This should work with dual paraboloid maps too for a paraboloid highlight.

7. Extensions • Extensions are where its at • nVidia extensions are good • Extensions on SGI? Where? SGIS_?

8. nVidia Extensions • EXT_blend_subtract • C’ = (Cs * S) - (Cd * D), clamped to 0 • Ben’s stuff? • EXT_light_max_exponent • Makes Phong exponent very high • Diefenbach’s thesis: Phong -> BRDF

9. nVidia Extensions • EXT_paletted_textures • Color palette with texels containing indices • Quake, PSX uses these to reduce texture memory • Also why original Quake was so brown • Might be able to use in house (iffy)

10. nVidia Extensions • EXT_texture_cube_map • Not just a view independent low distortion mapping • More like a vector to vector lookup table • Many good things flow from here • EXT_filter_anisotropic • This is a good part of why distant roads are blurry in computer graphics

11. nVidia Extensions • EXT_vertex_weighting • Can associate two transform matrices to a single vertex • Could do something like Cohen’s 3D morph with EXT_vertex_weighting along a spline • NV_register_combiners • Can set options on texture (up to 4 texture inputs), color, and fog. Good but complicated.

12. nVidia Extensions • NV_texgen_reflection • Use raw (rx, ry, rz) eye-space reflected vector to index a map

13. Everybody Else • EXT_pixel_transform • PixelZoom-like but matrix applied to rasterizer • EXT_polygon_offset • Nudge depth buffer forward or back • Good for multipass without multitexture

14. More Extensions • EXT_fragment_lighting • Adds lighting stage to OpenGL • *The* mechanism for per-pixel lighting • Renderman in OpenGL would use this • PixelFusion is going to use this • EXT_multitexture • Multitexture

15. More Extensions • SGIX_depth_texture • For shadows • Adds RGBAZ • SGIX_pixel_texture • Color components -> texture components • RG(B) -> ST(U) • Wolfgang Heidrich wrote a whole paper on it! • Combing with env maps is key

16. Even More Extensions • SGI_cushion • Adds ‘cushion buffers’ to help achieve constant frame rate • Seems like it will start drawing next one if the earlier one finishes before vertical retrace • SGIX_shadow • Allows <=, => on R part of interpolated (S,T,R) per vertex (??? Confusing ???)

17. HP & WIN Extensions • HP_occlusion_test • Can find non-visibility of geometry based on whether boxing geometry is visible • Render and query if depth buffer changes • WIN_phong_shading • Phong shading per pixel

18. Vendor Demos • nVidia trounces them all • Check out BlendView utility (needs DX7) • Very good way to gain intuition • ATI has a simpler one for the TNT • Runs on NT • Very good way to gain intuition as well • Highlights dire need for multitexture (Quake)

20. Combiners • Combiners are even worse • EIGHT stages of blending • Can also do dot product (per pixel lighting anyone?)

21. Gloss Mapping • Modulate sphere map reflection with alpha of another texture • Good for house group! • glBlendFunc is KEY for this and general modulation effects • Originally from ATI (as far as I know)

22. Specular vs. Gloss Mapping

23. Applied to House

24. glBlendFunc + Offset • For scuffs and colored glasses

25. What kind of FX? • Lights with shafts of light (through door) • Combing with animation for dust • Scuffs marks that affect a highlight • Grains in metals (brushed look) • Rough surfaces, grains • Wallpapers (different reflectances) • Marble (good when combined with reflect)

26. More FX • Refraction mapping • Wolfgang Heidrich invented that one • Slow on SGIs for a single polygon • Maybe in future could be used for planar glass simulation • SGI actually has a REFRACT texture generation mode (in gl.h)

27. Blend + Offset + Highlight • Plus reflection plus convolution plus view independent cube map plus bump map plus pixel textures plus scuffs… • The point is that the more realism you want, the more passes you need (at least for now)

28. Problem • How many textures can the IR combine at once (2?) • Kenny/Rui stuff uses no multitexture • GeForce can do 4 plus has funky combinings and texture generation modes • Next GeForce --> 8 textures at once??? • PixelFusion --> Programmable pixel shading (by July I think)

29. Idea • Create multipass versions for SGI • Try to see if single pass can be achieved on GeForce • Problem of texture memory • Need at *least* 64 megs • Highlight maps, bump maps all make it more • Palletized textures to the rescue?

30. What next? • HYR is the key to the next set of visual effects for these environments • Unfortunately, so are new extensinons :( • Supporting many types of mappings and passes • Like the current .atr/.fff idea but bigger • Still only an idea of HYR but something is there • Quake 3 Shader Manual

31. Bonus: Siggraph Paper • How to make images with alpha? • Start with an image that already has alpha • hurricane.tif • Import to Photoshop and alpha is another layer • From there it is EZ!

32. Bonus: Siggraph Paper • Making a Dual Paraboloid Map • Use GL_EXT_NORMAL_MAP and draw a mesh in the shape of the parabola • Normals are from center to mesh point • Then cube map… again EZ!

33. Converting • Cube map to Dual Paraboloid Map DP works on SGI too! Can do view independence on SGI!