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Real-Time Rendering

Real-Time Rendering. TEXTURING Lecture 02 Marina Gavrilova. Brief Outline. Basic Concept Texture Wrapping Magnification filter Minification filter Multi-Texturing Dynamic Texture Texture mapping methods.

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Real-Time Rendering

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  1. Real-Time Rendering TEXTURING Lecture 02 Marina Gavrilova

  2. Brief Outline • Basic Concept • Texture Wrapping • Magnification filter • Minification filter • Multi-Texturing • Dynamic Texture • Texture mapping methods

  3. Texture: Variation of surface diffusion, color, glossiness and other reflective photometry The heart of today’s computer graphics Texture Pixel = Texel Polygon is filled using texel values. Texture coordinate associates a screen pixel with a texel Concept of Texture

  4. Texturing a surface

  5. Texture mapping

  6. Texture mapping in computer games Color texture Environment mapping Alpha mapping Bump mapping Multi-texturing

  7. Basic Texturing concept • Modify the value used in the lighting equation • Basic Texture = per pixel object color • Steps: • Assign UV texture coordinates to vertices of a polygon (i.e. triangle) • Interpolate texture UV coordinate for each fill pixel during rasterization of the triangle • Lookup texel value from texture using UV coord. • Use texel value in lighting equation

  8. Texture Method • Texture pipeline used in rendering platforms to use hardware accelerations • U,V[0,1]  scaled texel coordinate • Texture resolution is a power of 2 (i.e. 256 x 256 texels)

  9. Texture Pipeline • Compute object space location • Use projector function to find (u,v) • Use corresponding functions to find texel • Apply value transform function • Modify illumination equation value

  10. Texture Rendering

  11. Texture modes • When UV value goes beyond the range [0,1] • i.e. uv= (-1,-1)  (2,2) (see below) • Allow simple and small textures to render large complex objects Tile Mirror Clamp Border

  12. Three dimensional texture coordinate (u,v,w) • 2D texture wrapping can be difficult for complex object • 3D texture mapping use (u,v,w) coordinate for texture address • Result is uniform texture distribution on a surface

  13. Texture magnification • When 1 texel = n pixels (n>1) • Visual Pixelation effect prominent • Solution: apply magnification filter Bilinear No Filter Bilinear No Filter

  14. Bilinear Filtering • Four pixel linear Interpolation (2x2) • Fast but low quality

  15. Bicubic • Not yet used in realtime graphics • Up to 4x4 pixel interpolation • Good quality • Slow

  16. Minification filter • When n texel = 1 pixel • Aliasing distortion is present • Annoying artifact during animation • Solution: MIP mapping, min-filters

  17. Min filters • Nearest • MIP • Summed area

  18. MIP Mapping (Base Concept) • Have multiple copy of a texture with reduced resolution (factor of 2) • I.e. (256x256), (128,128), (64,64),…(1,1) • Determine LOD from neighboring pixel UV difference (spacing)

  19. Anisotropic Filtering Trilinear MIP-MAPPING Anisotropic Filtering

  20. Texture caching and compression • Complex scene require large amount of texture • Texture Memory is limited • Texture management: Load only smaller LODs for distant objects • Use Clip-maps: load a small segment of high LOD texture • S3TC (6:1) compression  DirectX standard • Use two colors for a 4 color ramp • Represent 16 pixels using 4 colors • 2 bit per pixel, 16 bit per color  Average 4 bit per pixel

  21. Multi-pass rendering • Rendering the same geometry several times • Integrate different photometric components • I.e. Quake III has 10 rendering passes

  22. Multi-texturing • Combine two or more textures • Could be performed in one rendering pass • Pixel value is computed using values from different texture stages

  23. Multi-texture & Pixel-shader

  24. Texture Effects Variety of realistic 3D effects can be created by manipulating textures of a 3D geometry

  25. Texture Animation • Dynamic animated texture • Store combined static frames as 1 image • Use different UVs to animate frames UV=(0.25,0.25) UV=(0.5,0.5) Frame 5

  26. Transparency Alpha mapping = +

  27. Billboarding • Create complex objects using texture and simple geometry • Used extensively in particle rendering systems • Use faceted quads  normal of the quad equals camera direction • Used frequently in games • High performance

  28. Multi Textured Gloss Mapping

  29. Reflection/Environment mapping Blinn & Newells method:

  30. Other environment mapping Cube Mapping

  31. Bump Mapping • Per-pixel normal • Use cubemaps for normal

  32. Bump mapping • Use cubemap and multi-texture pass • Or use High level shading Language (HLSL) in nvidia

  33. Other texture teqniques • Detail Textures (i.e. flight simulator) • Procedural Texture • Anti-aliasing • Motion blur • Realistic shading • Volumetric Texture • Image processing using texture passes • Exposure control (Dynamic Range)

  34. End of Lecture 02 Questions?

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