1. Bump Mapping -1 Three scales of detail on an object
Macro-features that cover many pixels
Represented by vertices and triangles
Micro-features that are substantially smaller than a pixel
Encapsulated in the shading (lighting) model
Simulates the light interaction of a surface’s microscopic geometry; e.g., shiny objects are microscopically smooth, and diffuse surfaces are microscopically rough
Meso-features that are a few pixels across
Describe everything between macro- and micro scales
Contains detail that is too complex to render using polygons, but that is large enough for viewers to see changes in curvature over a few pixels
Winkles on faces
Graphics –U, Chap 4 Texture Mapping

2. Bump Mapping -2
A large family of small-scale detail representation techniques
By modifying the per-pixel shading routine
Give a more 3D appearance than texture mapping, but less than actual geometry
Bump mapping
A family of methods that are used for mesoscale modeling
Adjust shading parameters at the pixel level in such a way that the viewer perceives small perturbation away from the base geometry, which actually remains flat
Blinn’s methods, normal mapping, Parallax mapping, Relief mapping
Graphics –U, Chap 4 Texture Mapping

3. Bump Mapping -3
Graphics –U, Chap 4 Texture Mapping

4. Bump Mapping -4 (height field values)
Graphics –U, Chap 4 Texture Mapping

5. Bump Mapping -5 Blinn’s methods
Through variations in surface normal
Surface normal is perturbed according to a 2D bump map.
This tricks a local reflection model into producing appearance of bumpy details on a smooth surface
The geometry does not change
Bump map
Two signed value (bu, bv)
Used to scale two vectors that are perpendicular to normal
A heightfield
Used to derive (bu, bv)
Graphics –U, Chap 4 Texture Mapping

6. Bump Mapping -6 Bump map of two signed values (bu, bv)
(height field values)
Bump map of two signed values (bu, bv)
Bump map of highfield values
Graphics –U, Chap 4 Texture Mapping

7. Bump Mapping -7 (height field values)
Graphics –U, Chap 4 Texture Mapping

8. Bump Mapping -8 Let P(u, v) be a parametric surface
Perturb the normal N to N’
N’ is the normal of offset surface P’
The displacement must lie on the tangent plane of P
Two arrays that contain partials of B(u,v) can be precomputed.
Last terms can be
neglected if B(u,v)
is small.
Graphics –U, Chap 4 Texture Mapping

9. Bump Mapping -9
Graphics –U, Chap 4 Texture Mapping

10. Bump Mapping -10
Graphics –U, Chap 4 Texture Mapping

11. Bump Mapping -11 on polygonal mesh
Pu x Pv is not normalized. Pu x Pv changes at different rate than D – not a desirable feature
A full implementation of the equation in a rasterizer is impractical
So computation is divided among a preprocessing, per-vertex, and per-pixel calculation
Compute Pu x Pv, Pv x N, N x Pu at vertices and interpolate them to polygon interiors. (with possible hardware support)
For each pixel inside the triangle
the perturbed normal vector is computed and normalized, with Bu and Bv read from a texture map
Compute the per-pixel lighting
must be in tangent space to get stable bump mapping for animated or deformed objects!!
Graphics –U, Chap 4 Texture Mapping

12. Bump Mapping -12 on polygonal mesh
Emboss bump mapping
Borrowed from image embossing
One of the first methods for real-time bump mapping
A cheap bump mapping implementation, but not really bump mapping
Uses diffuse lighting only and has no specular effect
Under-sampling artifacts
Possible on today’s hardware
If it looks ok, do it!
Real bump mapping uses per-pixel lighting based on the perturbed normal vectors.
Graphics –U, Chap 4 Texture Mapping

13. Bump Mapping -13 on polygonal mesh
Dot product (Dot 3) bump mapping
The primary method for modern graphics hardware
Bump map texture stores the actual normal N’ to be used for bump mapping
The normal defined in pixel’s tangent space
Per-fragment lighting computed in pixel’s tangent space: N’  L (or diffuse) and (N’  H)^8 (for specular)
Graphics –U, Chap 4 Texture Mapping

14. Dot3 bump map -1 Normal map Bump map image
Graphics –U, Chap 4 Texture Mapping

15. Dot3 bump map -2 For a light source
The light source’s location is transformed to the surface’s tangent space basis at each triangle’s vertex
Interpolate among the un-normalized light vectors and normalize the resulting vector, which is converted to 8-bits values in the range [-1, 1]
By indexing to a specially build cubic environment map using the vector direction, any vector can be quickly renormalized.
The cubic environment map stores normalized vectors, as 8-bit signed values, for each direction
The normal from the normal map is then combined with the interpolated light vector at each pixel using dot product
Performed by a special texture blending function provided precisely for this purpose
This step obtains diffuse lighting
Graphics –U, Chap 4 Texture Mapping

16. Dot3 bump map -3 References (available in NVIDIA developer)
Specular lighting can also be easily derived
Instead of using the vector to the light, interpolate the half angle vector H
H=(L+v)/|L+v|, and dot(r, v) = dot(n, H)
Using pixel shader, the dot (n, H) specular term can be raised to the 8th power
References (available in NVIDIA developer)
A Practical and Robust Bump-mapping Technique for Today’s GPUs by Mark J. Kilgard, NVIDIA Corporation
Hardware bump mapping by D. Sim, in Game Programming Gems
Graphics –U, Chap 4 Texture Mapping

17. Dot3 bump map -4 Given a mesh and a normal map For each polygon
The light source’s location is transformed to the surface’s tangent space basis at each vertex
For each pixel
Interpolated the un-normalized light vector, and normal it using the cubic environment map
Dot product the light vector and the normal at the normal map, i.e., dot(n, L), using texture-blending.
Interpolated the un-normalized half angle vector, and normalize it using the cubic environment map
Dot product the normal at the normal map and the half angle vector, i.e., dot(n, H), using texture-blending, and then raised to the power
Graphics –U, Chap 4 Texture Mapping

18. Dot3 bump map -5 Vector normalization cube map
Performs per-pixel normalization
Denormalized vector (s, t, r)
Use the component of the largest magnitude to determine the pierced cube map face
+x, -x, +y, -y, +z, -z
The remaining two components are divided by the component of the largest magnitude
This effectively projects these two components onto the selected face
The two projected components are scaled and biased to the [0, 1] texel range, depending on the selected face to compute a 2D texture coordinate.
Graphics –U, Chap 4 Texture Mapping

19. Dot3 bump map -6 Vector normalization cube map
Graphics –U, Chap 4 Texture Mapping

20. Dot3 bump map -7 [Mark J. Kilgard] Result Height field texture
Color texture modulated by the diffuse contribution
computed using a normal bump map
Specular contribution computed using
a normalized version of normal map
Result
Height field texture
[Mark J. Kilgard]
Graphics –U, Chap 4 Texture Mapping

21. Dot3 bump map -8 Dot3 Bump Mapping Height field texture
Graphics –U, Chap 4 Texture Mapping

22. Dot3 bump map -9 Original texture GLBump2 demo!! Bump map
Graphics –U, Chap 4 Texture Mapping

23. Dot3 bump map -10 Bump map + shadowing md2shader demo!!
Graphics –U, Chap 4 Texture Mapping

24. Dot3 bump map -11 Bump map + shadowing md2shader demo!!
[Crysis on line game]
Graphics –U, Chap 4 Texture Mapping

25. Dot3 bump map -12 Graphics –U, Chap 4 Texture Mapping Gouraud shading
Phong shading
Phong shading with
Bump map
Graphics –U, Chap 4 Texture Mapping

26. Dot3 bump map -13 A wavy height field bump map Bump mapping effect
Gouraud shading
Phong shading
Phong shading with
Bump map
A wavy height field bump map
Bump mapping effect
Graphics –U, Chap 4 Texture Mapping

27. Displacement mapping
Sample the height field to find the amount of displacement, and then displace each vertex along its normal.
Adds surface detail, while resulting correct silhouette and no parallax errors, and also can create model itself
Modeling
Example: Terrain = a flat plane + a displacement map
Base surfaces: mesh, subdivision surfaces
Reference
Displacement mapping on the GPU – State of art, by Szirmay-Kalos and Umenhoffer, CGF, Vol. 25, No. 3, 2006
Displacement Mapping, by Michael Doggett, ATI Research
GDC 2003 Displacement Mapping, by Tom Forsyth
See GDC2003-DisplacementMappingNotes.pdf from NVIDIA Developer
Graphics –U, Chap 4 Texture Mapping

28. Displacement mapping Displacement map: Store scalar displacement
Graphics –U, Chap 4 Texture Mapping

29. Displacement mapping Example
Graphics –U, Chap 4 Texture Mapping

30. Displacement mapping Example
Graphics –U, Chap 4 Texture Mapping

31. Displacement mapping Base surface and maps
Low-poly “base” mesh
Derived using polygon simplification
2D-to-3D mapping
Mesh parameterization
Maps
Height-field scalar displacement map
Noraml map
Most tools apply to both normal and displacement maps
Graphics –U, Chap 4 Texture Mapping

32. Displacement mapping Deriving maps
Ray casting based method
A ray is cast from that position along the interpolated normal, and the intersection with high-polygon mesh is found
The normal of the high-polygon mesh is written to normal map
The distance along the ray to the intersection point is written to the displacement map
Based on a high-polygon mesh and a parameterization
Derive the displacement and normal maps for low-polygon base meshes
Each texel on the map has a single position on the low-polygon mesh
Graphics –U, Chap 4 Texture Mapping

33. Displacement mapping Rendering
Take sample points and displace them perpendicularly to the macrostructure surface with the distance obtained from the map.
Per-vertex displacement map
Sample points can be vertices of the tessellated mesh
GPU per-vertex displacement mapping using vertex shader or geometry shader
Displaced geometry goes through rendering pipeline
Per-pixel displacement map (inverse mapping)
Sample points corresponding to the texel centers
Surface details are added when color texturing takes place.
GPU-based: ray tracing using fragment shader [from 1998]
Graphics –U, Chap 4 Texture Mapping

34. Per-vertex displacement mapping
[DP on the GPU: State of art]
Graphics –U, Chap 4 Texture Mapping

35. Per-vertex displacement mapping
[Moule/McCool: Efficient bounded adaptive tessellation of displacement maps]
Graphics –U, Chap 4 Texture Mapping

36. Per-vertex displacement mapping
[DP on the GPU: State of art]
[Moule/McCool: Efficient bounded adaptive
tessellation of displacement maps]
Graphics –U, Chap 4 Texture Mapping

37. Per-vertex displacement mapping Problems
The number of vertices can be very high <-> the aim of DM
GPUs have usually more pixel-processing power than vertex-processing power
Pixel shaders are better equipped to access textures.
Texture access in vertex shader is slower than in the fragment shader.
Vertex shader always executes once for each vertex in the model, even to invisible or hardly visible parts
Graphics –U, Chap 4 Texture Mapping

38. Per-pixel displacement mapping
Vertex shader process only the base mesh
Surface height map is taken into account when fragments are processed
Use ray tracing to resolve the visibility problem
Ray tracing into height field to obtain the texture coordinate of the visible point, which are used to fetch color and normal vector.
For each processed point (u, v, 0) in tangent space, fragment shader finds the point of the height field which is really seen by the ray connecting (u, v, 0) and the pixel center.
Ray direction: tangent space view vector
Graphics –U, Chap 4 Texture Mapping

39. Per-pixel displacement mapping
[DP on the GPU: State of art]
Graphics –U, Chap 4 Texture Mapping

40. Per-pixel displacement mapping
[DP on the GPU: State of art]
Graphics –U, Chap 4 Texture Mapping

41. Multitexturing -1
Two or more textures are applied in a single rendering pass
Hardware supported to render in a single pass
Multiple textures can be fetched when processing a single fragment
Draw object once with several textures, some of which can be dynamically modified. E.g.,
The texture map may remain unchanged from frame to frame while the light map may be updated by a dynamic light and the fog map may be changed by the moving camera
The texture coordinate and vertex correspondence can be different for each texture map
Reference
See Real Time Rendering, 2nd ed., p146
See JL Mitchell’s page at
Graphics –U, Chap 4 Texture Mapping

42. Multitexturing -2 Multitexturing can Save rendering passes
Allows more complex shading models than does the application of a single texture per pass
Example: compute a lighting model with expression AB+CD, where each variable represents a different color texture’s value
Impossible to evaluate without multitexturing or using off-screen rendering (stores images that can be combined later)
A multipass rendering algorithm could combine AB in two passes and add C in the next, but it could not fold in D because C would already have been added to AB. There is no place to keep C separate from AB, since only one color can be stored in the frame buffer.
Graphics –U, Chap 4 Texture Mapping

43. Multitexturing -3
Combine the results of these texture accesses, a texture blending cascade is defined that is made up of a series of texture stages.
Graphics –U, Chap 4 Texture Mapping

44. Multitexturing -3 Two maps: a color map and a light map Texture map
Graphics –U, Chap 4 Texture Mapping

45. 3D Texture Mapping - 1
Texture is determined by the intersection of the surface with the predefined 3D texture field.
Texture field is obtained by procedure generation. Vertex coordinates are used to index a procedure (e.g. 3D noise function) that defines the 3D texture field for that point.
Advantages
is successful at simulating turbulence (e.g., marble objects).
eliminates mapping problems.
objects of arbitrary complexity can receive a texture in a coherent fashion.
Graphics –U, Chap 4 Texture Mapping

46. 3D Texture Mapping - 2 3D texture mapping in object space
Graphics –U, Chap 4 Texture Mapping

47. 3D Texture Mapping - 3 3D mapping and 3D noise
Graphics –U, Chap 4 Texture Mapping

48. 3D Texture Mapping - 4
Graphics –U, Chap 4 Texture Mapping