CSE 167: Introduction to Computer Graphics Lecture #8: Texture Mapping
CSE 167: Introduction to Computer Graphics Lecture #8: Texture Mapping Jürgen P. Schulze, Ph.D. University of California, San Diego Spring Quarter 2015 Announcements Homework 4 due Friday at 1pm Midterms to be returned on Thursday answers given in class 2 Lecture Overview Texture Mapping Overview Wrapping Texture coordinates Anti-aliasing 3 Large Triangles Pros: Often sufficient for simple geometry Fast to render Cons: Per vertex colors look boring and computer-generated 4 Texture Mapping Map textures (images) onto surface polygons Same triangle count, much more realistic appearance 5 Texture Mapping Goal: map locations in texture to locations on 3D geometry (1,1) Texture coordinate space Texture pixels (texels) have texture coordinates (s,t ) t Convention Bottom left corner of texture is at (s,t ) = (0,0) (0,0) Top right corner is at (s,t ) = (1,1) s Texture coordinates 6 Texture Mapping Store 2D texture coordinates s,t with each triangle vertex v1 (s,t ) = (0.65,0.75) (1,1) v0 (s,t ) = (0.6,0.4) (0.65,0.75) v2 t (s,t ) = (0.4,0.45) (0.4,0.45) (0.6,0.4) Triangle in any space before projection (0,0) s Texture coordinates 7 Texture Mapping Each point on triangle gets color from its corresponding point in texture v1 (1,1) (s,t ) = (0.65,0.75) (0.65,0.75) v0 t (s,t ) = (0.6,0.4) (0.4,0.45) (0.6,0.4) v2 (s,t ) = (0.4,0.45) (0,0) Triangle in any space before projection s Texture coordinates 8 Texture Mapping Primitives Modeling and viewing transformation Shading Projection Rasterization Fragment processing Includes texture mapping Frame-buffer access (z-buffering) 9 Image Texture Look-Up Given interpolated texture coordinates (s, t) at current pixel Closest four texels in texture space are at (s 0,t 0), (s 1,t 0), (s 0,t 1), (s 1,t 1) How to compute pixel color? t1 t t0 s0 s s1 10 Nearest-Neighbor Interpolation Use color of closest texel t1 t t0 s0 s s1 Simple, but low quality and aliasing 11 Bilinear Interpolation 1.
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