CS-184: Computer Graphics Lecture #11: Texture and Other Maps - PowerPoint PPT Presentation

1 CS-184: Computer Graphics Lecture #11: Texture and Other Maps Prof. James O’Brien University of California, Berkeley V2015-S-11-1.0 2 Today • Texture Mapping • 2D • 3D • Procedural • Bump and Displacement Maps • Environment Maps • Shadow Maps 2

3 Surface Detail • Representing all detail in an image with polygons would be cumbersome Specific details Structured noise Pattern w/ randomness Section through volume Bumps 3 4 2D Texture Mapping of Images • Use a 2D image and map it to the surface of an object Color Specular Bump 4

5 2D Texture Mapping of Images 5 6 2D Texture Mapping of Images 6

7 2D Texture Mapping of Images 7 8 2D Texture Mapping of Images 8

9 2D Texture Mapping of Images • Example of texture distortion 9 10 Texture Coordinates • Assign coordinates to each vertex • Within each triangle use linear interpolation • Correct for distortion! t s 10

11 MIP Map • Pre-compute filtered versions of the texture • A given UV rate is some level of the texture • Tri-linear filtering UV × map level 11 12 Procedural Textures • Generate texture based on some function • Well suited for “random” textures • Often modulate some noise function [Foley et al. / Perlin] 12

13 Assigning Texture Coordinates • Map a simple shape onto object by projection • Sphere, cylinder, plane, cube • Assign by hand • Use some optimization procedure 13 14 Repeating Textures • Image Tiles allow repeating textures • Images must be manipulated to allow tilling • Often result in visible artifacts • There are methods to get around artifacts.... 14

15 Repeating Textures • Image Tiles allow repeating textures • Images must be manipulated to allow tilling • Often result in visible artifacts • Artifacts not an issue for artificial textures 15 16 Non-Color Textures Color Specular Bump 16

17 Bump Mapping No bump mapping With bump mapping Images by Paul Baker www.paulsprojects.net 17 18 Bump Mapping • Add offset to normal • Offset is in texture coordinates S,T,N • Store normal offsets in RGB image components • Should use correctly orthonormal coordinate system • Normal offsets from gradient of a grayscale image b ( u , v ) = [ s , t , n ]( u , v ) = ∇ i ( u , v )  ∂ � T ∂ u , ∂ ∇ = ∂ v 18

19 Bump Map Example Catherine Bendebury and Jonathan Michaels CS 184 Spring 2005 19 20 Displacement Maps • Actually move geometry based on texture map • Expensive and difficult to implement in many rendering systems • Note silhouette Bump Displacement 20

21 Normals Maps [Paolo Cignoni] 21 22 Texture Coordinate Assignment [Wolfe / SG97 Slide set] 22

23 Texture Coordinate Assignment • Planar projection u Marschner, 2014 v 23 24 Texture Coordinate Assignment • Spherical Coordinates Marschner, 2014 24

25 Texture Coordinate Assignment • Spherical Projection Marschner, 2014 25 26 Texture Coordinate Assignment • Cylindrical Projection spherical cylindrical Marschner, 2014 26

27 Texture Coordinate Assignment • Multiple Projections [Tito Pagan] 27 28 Texture Coordinate Assignment • 3D Textures [Wolfe / SG97 Slide set] 28

29 Environment Maps • Environment maps allow crude reflections • Treat object as infinitesimal • Reflection only based on surface normal • Errors hard to notice for non-flat objects 29 30 Environment Maps 30

31 Environment Maps (u,v) = (1,1) z x = y= z u = y + x y 2 x x right face has x > |y|, x > |z| v v = z + x u 2 x (u,v) = (0,0) x = -y= -z 31 32 Environment Maps • Sphere based parameterization • Wide angle image or • Photo of a silver ball Images by Paul Haeberli 32

33 Environment Maps [Dror, Willsky, & Adelson 2004] (a) (b) Figure 2. (a). A shiny sphere rendered under photographically acquired real-world illumination. (b). The same sphere rendered under illumination by a point light source. 33 34 Environment Maps • Used in 1985 in movie Interface • Effect by group from the New York Institute of Technology Note errors 34

35 Environment Maps • Used in 1985 in movie Interface • Effect by group from the New York Institute of Technology 35 36 Shadow Maps • Pre-render scene from perspective of light source • Only render Z-Buffer (the shadow buffer) • Render scene from camera perspective • Compare with shadow buffer • If nearer light, if further shadow 36

37 Shadow Maps Shadow Buffer Image w/ Shadows From Stamminger and Drettakis SIGGRAPH 2002 Note: These images don’t really go together, see the paper... 37 38 Deep Shadow Maps • Some objects only partially occlude light • A single shadow value will not work • Similar to transparency in Z-Buffer From Lokovic and Veach SIGGRAPH 2000 38