Texture Mapping
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This document discusses texture mapping in computer graphics. Texture mapping involves applying 1D, 2D, or 3D images to geometric primitives. Textures can be used to simulate materials, reduce geometric complexity, perform image warping, and create reflections. Texture mapping works by flowing image and geometry data through separate pipelines that join at the rasterization stage. The document outlines steps for applying textures including specifying the texture, assigning texture coordinates to vertices, and setting texture parameters like wrapping and filtering modes.
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Generating Texture Coordinates
• Automatically generate texture coords
glTexGen{ifd}[v]()
• specify a plane
– generate texture coordinates based upon distance from
plane
• generation modes
– GL_OBJECT_LINEAR
– GL_EYE_LINEAR
– GL_SPHERE_MAP
0 DCzByAx
Budditha Hettige](https://image.slidesharecdn.com/tm-170814145432/85/Texture-Mapping-15-320.jpg)
• GL_TEXTURE_ENV_MODE modes
– GL_MODULATE
– GL_BLEND
– GL_REPLACE
• Set blend color with
GL_TEXTURE_ENV_COLOR
Budditha Hettige](https://image.slidesharecdn.com/tm-170814145432/85/Texture-Mapping-21-320.jpg)
Texture Mapping
- 1. CSC 307 1.0 Graphics Programming Budditha Hettige Department of Statistics and Computer Science
- 3. 3 • Apply a 1D, 2D, or 3D image to geometric primitives • Uses of Texturing – simulating materials – reducing geometric complexity – image warping – reflections Texture Mapping CPUCPU DLDL Poly.Poly. Per Vertex Per Vertex RasterRaster FragFrag FBFB PixelPixel TextureTexture Budditha Hettige
- 5. 5 Texture Mapping and the OpenGL Pipeline geometry pipelinevertices pixel pipeline image rasterizer • Images and geometry flow through separate pipelines that join at the rasterizer – “complex” textures do not affect geometric complexity Budditha Hettige
- 6. 6 Texture Example • The texture (below) is a 256 x 256 image that has been mapped to a rectangular polygon which is viewed in perspective Budditha Hettige
- 7. 7 Applying Textures I • Three steps specify texture • read or generate image • assign to texture • enable texturing assign texture coordinates to vertices specify texture parameters • wrapping, filtering Budditha Hettige
- 8. 8 Applying Textures II – specify textures in texture objects – set texture filter – set texture function – set texture wrap mode – set optional perspective correction hint – bind texture object – enable texturing – supply texture coordinates for vertex • coordinates can also be generated Budditha Hettige
- 9. 9 Texture Objects • Like display lists for texture images – one image per texture object – may be shared by several graphics contexts • Generate texture names glGenTextures( n, *texIds ); Budditha Hettige
- 10. 10 Texture Objects (cont.) • Create texture objects with texture data and state glBindTexture( target, id ); • Bind textures before using glBindTexture( target, id ); Budditha Hettige
- 11. 11 • Define a texture image from an array of texels in CPU memory • glTexImage2D( target, level, components, w, h, border, format, type, *texels ); – dimensions of image must be powers of 2 • Texel colors are processed by pixel pipeline – pixel scales, biases and lookups can be done Specify Texture Image CPUCPU DLDL Poly.Poly. Per Vertex Per Vertex RasterRaster FragFrag FBFB PixelPixel TextureTexture Budditha Hettige
- 12. 12 Converting A Texture Image • If dimensions of image are not power of 2 • gluScaleImage( format, w_in, h_in, type_in, *data_in, w_out, h_out, type_out, *data_out ); – *_in is for source image – *_out is for destination image • Image interpolated and filtered during scaling Budditha Hettige
- 13. 13 Specifying a Texture: Other Methods • Use frame buffer as source of texture image – uses current buffer as source image glCopyTexImage1D(...) glCopyTexImage2D(...) • Modify part of a defined texture glTexSubImage1D(...) glTexSubImage2D(...) glTexSubImage3D(...) • Do both with glCopyTexSubImage2D(...), etc. Budditha Hettige
- 14. 14 • Based on parametric texture coordinates • glTexCoord*() specified at each vertex s t 1, 1 0, 1 0, 0 1, 0 (s, t) = (0.2, 0.8) (0.4, 0.2) (0.8, 0.4) A B C a b c Texture Space Object Space Mapping a Texture CPUCPU DLDL Poly.Poly. Per Vertex Per Vertex RasterRaster FragFrag FBFB PixelPixel TextureTexture Budditha Hettige
- 15. 15 Generating Texture Coordinates • Automatically generate texture coords glTexGen{ifd}[v]() • specify a plane – generate texture coordinates based upon distance from plane • generation modes – GL_OBJECT_LINEAR – GL_EYE_LINEAR – GL_SPHERE_MAP 0 DCzByAx Budditha Hettige
- 17. 17 • Filter Modes – minification or magnification – special mipmap minification filters • Wrap Modes – clamping or repeating • Texture Functions – how to mix primitive’s color with texture’s color • blend, modulate or replace texels Texture Application Methods Budditha Hettige
- 18. 18 Filter Modes Texture Polygon Magnification Minification PolygonTexture Example: glTexParameteri( target, type, mode ); Budditha Hettige
- 19. 19 Mipmapped Textures • Mipmap allows for prefiltered texture maps of decreasing resolutions • Lessens interpolation errors for smaller textured objects • Declare mipmap level during texture definition glTexImage*D( GL_TEXTURE_*D, level, … ) • GLU mipmap builder routines gluBuild*DMipmaps( … ) • OpenGL 1.2 introduces advanced LOD controls Budditha Hettige
- 20. 20 Wrapping Mode • Example: glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP ) glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT ) texture s t GL_CLAMP wrapping GL_REPEAT wrapping Budditha Hettige
- 21. 21 Texture Functions • Controls how texture is applied • glTexEnv{fi}[v]( GL_TEXTURE_ENV, prop, param ) • GL_TEXTURE_ENV_MODE modes – GL_MODULATE – GL_BLEND – GL_REPLACE • Set blend color with GL_TEXTURE_ENV_COLOR Budditha Hettige
- 22. 22 Perspective Correction Hint • Texture coordinate and color interpolation – either linearly in screen space – or using depth/perspective values (slower) • Noticeable for polygons “on edge” • glHint( GL_PERSPECTIVE_CORRECTION_HINT, hint ) where hint is one of • GL_DONT_CARE • GL_NICEST • GL_FASTEST Budditha Hettige
- 23. 23 Is There Room for a Texture? • Query largest dimension of texture image – typically largest square texture – doesn’t consider internal format size • glGetIntegerv( GL_MAX_TEXTURE_SIZE, &size ) • Texture proxy – will memory accommodate requested texture size? – no image specified; placeholder – if texture won’t fit, texture state variables set to 0 • doesn’t know about other textures • only considers whether this one texture will fit all of memory Budditha Hettige
- 24. 24 Texture Residency • Working set of textures – high-performance, usually hardware accelerated – textures must be in texture objects – a texture in the working set is resident – for residency of current texture, check GL_TEXTURE_RESIDENT state • If too many textures, not all are resident – can set priority to have some kicked out first – establish 0.0 to 1.0 priorities for texture objects Budditha Hettige