Texture Mapping

1 .Texture Mapping CMSC435 UMBC *With lots of borrowing from the usual victims… 

2 . Motivation Flat and Boring “Textured” 

3 . Texture Mapping • Definition: mapping a function onto a surface; function can be: – 1, 2, or 3D – sampled (image) or mathematical function 3 

4 . Texture Mapping “Texture” Boring Geometry Texture  An image that’s mapped onto something Texel  Texture pixel (Also, an island in Denmark…) 

5 .Texture Mapping Interesting Geometry 

6 . Texture Mapping Mapping Function 2D Texture 3D Coordinate Coordinate Texture Image 

7 . Texture Coordinates u • Normalized 2D space – 0-1 on each axis v D3D • Letters vary: – U,V are most common – GL/RMan specs like s,t Texture Coordinates as RGB • Typically periodic t OGL s 

8 . Texture Tiling 0,0 0,0 0,1 0,2 1,0 2,0 Scale UV Coordinates  Alter texture frequency 0,0 0,0 0,4 0,8 4,0 8,0 

9 . Planar Mapping • For xy aligned plane • Reverse projection 9 

10 .Planar Mapping 10 

11 . Cylindrical Mapping • For cylinder with point – • Texture coordinates – 11 

12 .Cylindrical Mapping 12 

13 . Spherical Mapping • For sphere with point – • Texture coordinates 13 

14 .Spherical Mapping 14 

15 .Mapping onto Parametric Patches • Use scaled surface u,v parameters for texture u,v 15 

16 .Mapping onto Parametric Patches 16 

17 .Mapping onto Polygons Explicit per-vertex coordinates… Wikipedia 

18 . Texture Atlas • Properties of good UV layout: – Minimizes stretch – Maximize packing efficiency – Easy for artist to paint into • Unlike that one… – Automatic is possible, but manual often Zhou et al. preferred 

19 . Texture Atlas • Not always a 1:1 mapping 

20 . Texture Seams • Discontinuity at UV chart boundaries • Solutions: – Fix them: • Copy/Blend texels across boundary – Hide them • Armpits, ankles, backs of heads, under clothing Peter Kojesta (Gamasutra) 

21 . Environment Mapping • Surround scene with maps simulating surrounding detail 21 

22 . Distant Reflection • Look up reflection direction in reflection or environment map 22 

23 . Cubic Environment Maps • Pick a face based on largest normal component • Project onto the face – Divide through • Use resulting coordinates for 2D lookup 

24 . Spherical Environment Maps • Photograph of shiny sphere – Lookup based on x/y coordinates of normal DirectX Documentation 

25 . Texture All the Things • Texture/Albedo map (Catmull 74) • Reflection Map (Blinn and Newell 76) • Bump/Normal Map (Blinn 78 / Cohen 98) • Gloss Map (Blinn 78) • Transparency Map (Gardner 85) • Diffuse Reflectance (Miller and Hoffman 84) • Shadows, displacements, etc (Cook 84) • Tangent map (Kajiya 85) 25 

26 . Texture Sampling • Point Sampling – Map UV coordinate onto texel grid, grab corresponding texel • i = floor(u*width) • j = floor(v*height) – Just like in 1995 

27 .Point Sampling Point sampling under magnification 

28 . Filtered Sampling • Bilinear Filtering – Interpolate texels in 2x2 neighborhood • Top-left texel: – floor(u*(width-1)), floor(v*(height-1)) • Weight by fractional coordinates 

29 .Point Sampling Point sampling under magnification