Real-Time Relief Mapping on Arbitrary Polygonal Surfaces

1. Real-Time Relief Mapping on Arbitrary Polygonal Surfaces Fabio Policarpo Manuel M. Oliveira Joao L. D. Comba

2. Overview • Introduction • Related Work • Review of Relief Texture Mapping • Methods • Results • Discussion

3. Introduction Goals • Represent surface detail using textures • Apply to polygonal surfaces, allowing for deformation • Allow self-occlusions and per-pixel lighting effects Introduction > Related Work > Relief Texture Mapping > Methods > Results

4. Related Work • Bump mapping • Self-occlusions, shadows and silhouettes are not accounted for • Displacement mapping • Requires large amount of micro-polygons Introduction > Related Work > Relief Texture Mapping > Methods > Results

5. Related Work • View-dependent displacement maps • Pre-computes distances to a reference surface • Sampled along several view directions • Does not handle close up viewing well • Parallax Mapping • Uses per-texel depth • Texture coordinates along view direction are shifted based on depth • Only good for irregular/noisy bumps • No support for shadows Introduction > Related Work > Relief Texture Mapping > Methods > Results

6. Relief Texture Mapping • Uses image warping techniques and per-texel depth to create the illusion of geometric detail Introduction > Related Work > Relief Texture Mapping > Methods > Results

7. Relief Texture Mapping • Rendering of a height field requires a search for the closest polygon along the viewing ray • Overcome through a two-pass method: • Convert height field to conventional 2D texture using forward projection • Render texture as normal Introduction > Related Work > Relief Texture Mapping > Methods > Results

8. Representing 3D objects • Represent 3D geometry by relief texture mapping parallelepiped • Cannot be extended to arbitrary surfaces Introduction > Related Work > Relief Texture Mapping > Methods > Results

9. Relief Mapping Polygonal Surfaces • Uses modern graphics hardware • Because of fragment shaders, lighting is computed real-time Introduction > Related Work > Relief Texture Mapping > Methods > Results

10. Mapping relief data • Compute viewing direction, VD • Transform VD to tangent space of fragment • Use VD’ and texture coords (s,t) to compute the texture coords where VD’ hits depth of 1 Introduction > Related Work > Relief Texture Mapping > Methods > Results

11. Mapping relief data • Compute the intersection between VD’ and the height-field surface using a binary search starting with A and B • Perform the shading of the fragment using the attributes associated with the texture coordinates of the computed intersection point. Introduction > Related Work > Relief Texture Mapping > Methods > Results

12. Binary Search • Start with A-B line • At each step (8 steps): • Compute middle of the interval • Assign averaged endpoint texture coordinates and depth • Use averaged tex coords to access depth map • If stored depth value is less than computed depth value, the point is inside the surface • Proceed with one endpoint in and one out Introduction > Related Work > Relief Texture Mapping > Methods > Results

13. Linear Search • To find first point under surface, start at A, advance ray by δAB • δ is a function of the angle between VD’ and interpolated fragment normal • No more than 32 steps are taken in their implementation • Proceed with binary search (with less iterations) Introduction > Related Work > Relief Texture Mapping > Methods > Results

14. Shadowing • Visibility problem • Determine if light ray intersects surface • Do not need to know the exact point Introduction > Related Work > Relief Texture Mapping > Methods > Results

15. Dual Depth Relief Textures • Represent opaque, closed surfaces with only one texture • Second “back” layer is not used for rendering, but as a constraint for ray-height-field intersection Introduction > Related Work > Relief Texture Mapping > Methods > Results

16. Dual Depth Relief Textures Results Introduction > Related Work > Relief Texture Mapping > Methods > Results

17. Dual Depth Relief Textures Storage • Two depthmaps and a normal map can be stored in one texture • Since normals are unit length, you can store just x and y and use the other two components for depth values • Compute z @ run-time • Rendering is the same as described, except a point is in the represented object if front_depth <= point depth <= back_depth Introduction > Related Work > Relief Texture Mapping > Methods > Results

18. Results • Most objects rendered with 512x512 relief texture • 800x600 resolution at 85 fps • Written in Cg • 3GHz PC w/ 512 MB memory on NVIDIA GeForce 6800GT w/ 256 MB memory Introduction > Related Work > Relief Texture Mapping > Methods > Results

19. Results Introduction > Related Work > Relief Texture Mapping > Methods > Results

20. Results Introduction > Related Work > Relief Texture Mapping > Methods > Results

21. Results Introduction > Related Work > Relief Texture Mapping > Methods > Results

22. Results Introduction > Related Work > Relief Texture Mapping > Methods > Results

23. Results Introduction > Related Work > Relief Texture Mapping > Methods > Results

24. Results Introduction > Related Work > Relief Texture Mapping > Methods > Results

25. Conclusion • Provided method for mapping relief textures to arbitrary surfaces in texture space, allowing deformation • Provides correct shadowing, self-occlusion, and interpenetration with correct lighting • Presented an efficient ray-heightfield intersection algorithm • Extended relief maps with dual-depth textures