1. Texture Mapping
Fall, 2016

2. Textures Describe color variation in interior of 3D polygon
When scan converting a polygon, vary pixel colors according to values fetched from a texture

3. The Quest for Visual Realism

4. Surface Textures
Add visual detail to surfaces of 3D objects

5. 3D Rendering Pipeline
Texture Mapping

6. Texture Mapping Overview
Texture mapping methods
Parameterization
Mapping
Filtering
Texture mapping applications
Modulation textures
Illumination mapping
Bump mapping
Environment mapping
Image-based rendering
Non-photorealistic rendering

7. Parameterization Q: How do we describe where on the geometry
each color from the image should go?

8. Option: Varieties of projections
Plane Mapping
Cube Mapping
Cylinder Mapping
Sphere Mapping

9. Parameterization (Example 1)

10. Parameterization (Example 2)

11. Parameterization (Example 3)

12. Parameterization (Example 4)

13. Option: unfold the surface

14. Texture Mapping Overview
Texture mapping methods
Parameterization
Mapping
Filtering
Texture mapping applications
Modulation textures
Illumination mapping
Bump mapping
Environment mapping
Image-based rendering
Non-photorealistic rendering

15. Texture Mapping Steps: Define texture
Specify mapping from texture to surface
Lookup texture values during scan conversion

16. Texture Mapping When scan convert, map from …
Image coordinate system (x, y) to
Modeling coordinate system (u, v) to
Texture image (s, t)

17. Texture Mapping Texture mapping is a 2D projective transformation
Texture coordinate system (s, t) to
Image coordinate system (x, y)

18. Texture Mapping Scan conversion
Interpolate texture coordinates down/across scan lines
Distortion due to bilinear interpolation approximation
Cut polygons into smaller ones, or
Perspective divide at each pixel

19. Perspective-correct interpolation
Texture Mapping
Linear interpolation
Perspective-correct interpolation

20. Texture Mapping Overview
Texture mapping methods
Parameterization
Mapping
Filtering
Texture mapping applications
Modulation textures
Illumination mapping
Bump mapping
Environment mapping
Image-based rendering
Non-photorealistic rendering

21. Texture Filtering
Must sample texture to determine color at each pixel in image

22. Texture Filtering
Aliasing is a problem
Point Sampling
Area Filtering

23. Texture Filtering
Ideally, use elliptically shaped convolution filters

24. Texture Filtering Size of filter depends on projection warp
Can prefiltering images
Mip maps
Summed area tables

25. Mip Maps Keep textures prefiltered at multiple resolutions d v u
For each pixel, linearly interpolate between two closest levels (e. g. trilinear filtering)
Fast, easy for hardware u v d

26. Summed-area tables At each texel keep sum of all values down & right
To compute sum of all values within a rectangle, simply subtract two entries
Better ability to capture very oblique projections
But, cannot store values in a single byte

27. Texture Mapping Overview
Texture mapping methods
Parameterization
Mapping
Filtering
Texture mapping applications
Modulation textures
Illumination mapping
Bump mapping
Environment mapping
Image-based rendering
Non-photorealistic rendering

28. Modulation textures
Map texture values to scale factor

29. Illumination Mapping +
Map texture values to surface material parameter KA KD KS KT n
Key-frame
model
geometry
Decal skin
Bump skin
Gloss skin
WOW!
Result +

30. Stores heights: can derive normals
Bump Mapping
Texture values perturb surface normals
Bump map
Stores heights: can derive normals +
Bump mapped geometry =
geometry

31. Bump Mapping

32. Displacement Mapping Normal Mapping Problem Displacement Mapping
Doesn’t take into account geometric surface depth
Does not exhibit parallax
No self-shadowing of the surface
Coarse silhouettes expose the actual geometry being drawn
Displacement Mapping
Displace actual positions from Heightfield Map

33. Displacement Mapping

34. Displacement Mapping (Result)
Displacement Offset

35. Environment Mapping
Texture values are reflected off surface patch

36. Cube Mapping
Cube mapping is the norm nowadays
eye x y z n

37. Image-Based Rendering
Map photographics textures to provide details for coarsely detailed polygon model

38. Solid Textures Texture values indexed by 3D location (x, y, z)
Expensive storage, or
Compute on the fly
ex) Perlin Noise

39. Texture Mapping Summary
Texture mapping methods
Parameterization
Mapping
Filtering
Texture mapping applications
Modulation textures
Illumination mapping
Bump mapping
Environment mapping
Image-based rendering
Volume textures

40. Example) Quake 2 Models: Piece by Piece
Model Key Frames
Quake 2 interpolates between key frames

41. Example) Quake 2 Models: Piece by Piece
Knight model’s decal skin
Texture coordinates map
triangles to skin.
Note clever packing of
decal skin. Only half
face because triangles
“mirror” the face.

42. Example) Standard Quake 2: Model Rendering
Texture key-frame with decal skin +
Key-frame
model
geometry
Decal skin
Result

43. Example) GPU Bump-mapped: Quake 2 Model Rendering!
Bump-map model with bump, gloss, & decal skin
Bump skin +
Key-frame
model
geometry
WOW!
Result
Gloss skin
Decal skin

44. Example) Quake 2 Bump Mapping: Rendering Passes  (
) + (
) =
Diffuse
Decal
Specular
Gloss
Final result!

45. Example) More Bump-mapped Knight Examples
Different light positions and key-frames
All lighting including specular is computed per-fragment!

46. Example) Bump Mapping Models
Viva la difference

47. OpenGL Texture Mapping
Texture Mapping in OpenGL
Allows you to modify the color of a polygon surface
Textures are simply rectangular arrays of data (color, luminance, color+alpha). Individual values in a texture are called texels

48. OpenGL Texture Mapping : Step
Steps necessary to use texture mapping:
Create a texture object and specify the texture
Indicate how the texture is to be applied to each pixel
Enable texture mapping
Draw the scene, supplying both texture and geometric coordinates

49. OpenGL Texture Mapping : 2D Texture Specification
glTexImage2D(GLenum target, GLint level, GLint internalFormat, GLsizei width, GLsizei height, Glint border, GLenum format, Glenum type, const Glvoid *pixels);
target: GL_TEXTURE_2D
level: specifies the level of detail when using multi resolution textures. “0” is the base image, “n” is the n-th mipmap reduction image
internalFormat: an integer 1 to 4, or one of 38 symbolic constants
width, height: the dimensions of the texture (MUST BE power of 2)
format: the kind of pixel-data elements
type: the data-type of each element
pixels: array containing the texture image data
Ex) glTexImage2D(GL_TEXTURE_2D, 0, 3, iwidth, iheight,
0, GL_RGB, GL_UNSIGNED_BYTE, image);

50. OpenGL Texture Mapping : Values for Format and Type
Format Constants:
GL_COLOR_INDEX: A single color index
GL_RGB: A red component, followed by green & blue components
GL_RGBA: Like GL_RGB, followed by an alpha component.
GL_RED: A single red-color component
GL_GREEN: A single green-color component
GL_BLUE: A single blue-color component
GL_ALPHA: A single alpha-color component
Type Constants:
GL_UNSIGNED_BYTE: unsigned 8-bit integer
GL_BYTE: signed 8-bit integer
GL_UNSIGNED_SHORT: unsigned 16-bit integer
GL_SHORT: signed 16-bit integer
GL_INT: signed 32-bit integer
GL_FLOAT: single-precision floating point

51. OpenGL Texture Mapping : Texture Coordinates
You need to specify BOTH texture & geometric coordinates as you specify the object in your scene
glColor3f(1.0f, 0.0f, 0.0f);
glBegin(GL_TRIANGLES);
glNormal3d(0,0,-1);
glTexCoord2d(0,0);
glVertex3d(-100,-100,0);
glTexCoord2d(1,0);
glVertex3d(100,-100,0);
glTexCoord2d(0,1);
glVertex3d(-100,100,0);
glEnd();

52. OpenGL Texture Mapping : Texture Filtering
glTexParameteri( target, type, mode)
Target : GL_TEXTURE_1D, GL_TEXTURE_2D
Type : GL_TEXTURE_MIN_FILTER
Mode :
GL_NEAREST, GL_LINEAR, GL_NEAREST_MIPMAP_NEAREST, GL_LINEAR_MIPMAP_NEAREST, GL_NEAREST_MIPMAP_LINEAR GL_LINEAR_MIPMAP_LINEAR
Type : GL_TEXTURE_MAG_FILTER
GL_NEAREST or GL_LINEAR
Ex) glTexParameteri(GL_TEXTURE_2D, GL_TEXURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXURE_MIN_FILTER, GL_LINEAR);

53. No mipmapping
Mipmappping
Min / Max Filter : GL_NEAREST
Min / Max Filter : GL_LINEAR

54. OpenGL Texture Mapping : Texture Wrapping
glTexParameteri( target, type, mode)
Target : GL_TEXTURE_1D, GL_TEXTURE_2D
Type
GL_TEXTURE_WRAP_S
GL_TEXTURE_WRAP_T
mode
GL_CLAMP or GL_REPEAT
Wrap S : GL_CLAMP Wrap T : GL_CLAMP
Wrap S : GL_CLAMP Wrap T : GL_REPEAT
Wrap S : GL_REPEAT Wrap T : GL_CLAMP
Wrap S : GL_REPEAT
Wrap T : GL_REPEAT

55. OpenGL Texture Mapping : Texturing Functions
Indicate how the texture is applied to each pixel:
REPLACE or DECAL: Texture is painted on top of the fragment
MODULATE: Combine texture with fragment color. This technique is useful to combine the effects of lighting with texturing
BLEND: A constant color is blended with that of the fragment, based on the texture value
Ex) glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

56. OpenGL Texture Mapping : Texture Functions