1. Texture Mapping Fall, 2011

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 Cylinder MappingSphere MappingCube MappingPlane Mapping

9. Option: unfold the surface

10. Option: make an atlas

11. 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

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

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

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

15. 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

16. Texture Mapping Linear interpolationPerspective-correct interpolation

17. 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

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

19. Texture Filtering Aliasing is a problem Point SamplingArea Filtering

20. Texture Filtering Ideally, use elliptically shaped convolution filters

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

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

23. 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

24. 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

25. Modulation textures Map texture values to scale factor

26. Illumination Mapping Map texture values to surface material parameter  K A  K D  K S  K T  n Key-framemodelgeometryKey-framemodelgeometry Decal skin Bump skin Gloss skin WOW!ResultWOW!Result ++

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

28. Bump Mapping

29. Displacement Mapping Normal Mapping Problem  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

30. Displacement Mapping (Result) Displacement Offset

31. Environment Mapping Texture values are reflected off surface patch

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

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

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

35. 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

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

37. 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.

38. Example) Standard Quake 2: Model Rendering Texture key-frame with decal skin ++ ResultResult Key-framemodelgeometryKey-framemodelgeometry Decal skin

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

40. Example) Quake 2 Bump Mapping: Rendering Passes   ) + ( (( ) = DiffuseDiffuseGlossGlossSpecularSpecularDecalDecal Final result!

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

42. Example) Bump Mapping Models Viva la difference

43. 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

44. 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

45. OpenGL Texture Mapping : 2D Texture Specification 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);

46. 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

47. OpenGL Texture Mapping : Texture Coordinates 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();

48. 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);

49. Min / Max Filter : GL_NEAREST Min / Max Filter : GL_LINEAR No mipmappingMipmappping

50. 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

51. OpenGL Texture Mapping : Texturing Functions 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);

52. OpenGL Texture Mapping : Texture Functions