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2IV60 Computer Graphics set 10: Texture mapping

2IV60 Computer Graphics set 10: Texture mapping. Jack van Wijk TU/e. Texture mapping. Need more detail? Paste a picture! Texture: 1-D, 2-D and 3-D image Texture coordinates: Per vertex 1, 2 or 3 extra coordinates that point in the texture. H&B 18: 579-601. 1D Texture mapping 1.

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2IV60 Computer Graphics set 10: Texture mapping

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  1. 2IV60 Computer Graphicsset 10: Texture mapping Jack van Wijk TU/e

  2. Texture mapping Need more detail? Paste a picture! • Texture: 1-D, 2-D and 3-D image • Texture coordinates: Per vertex 1, 2 or 3 extra coordinates that point in the texture H&B 18: 579-601

  3. 1D Texture mapping 1 1D texture mapping: Color scale for visualization H&B 18-2:580-585

  4. (255,0,0) (128,128,0) (85,85,85) (0,255,0) (128,0,128) (0,128,128) (0,0,255) 1D Texture mapping 2 Interpolation of colors gives poor results… H&B 18-2:580-585

  5. s=1 s=0.75 s=0.5 s=0.5 s=0.5 s=0.25 s=0 1D Texture mapping 3 Coloring with 1D texture-map: better result s=1 s=0 H&B 18-2:580-585

  6. (s(u),t(v)) t (s,t) s 2D Texture mapping y (u,v) (x,y) v u x texture space object space image space H&B 10-17:629-634

  7. (s(u),t(v)) t (s,t) s Forward mapping Forward mapping: project texture to pixel y (u,v) (x,y) v u x texture space object space image space H&B 10-17:629-634

  8. (s(u),t(v)) t (s,t) s Backward mapping Backward mapping: lookup texture per pixel y (u,v) (x,y) v u x texture space object space image space H&B 10-17:629-634

  9. 2D Texture mapping triangles (s0, t0) (s,t) y (s0, t0) (s,t) color(s,t) t (s,t) (s2, t2) (s2, t2) (s1, t1) (s1, t1) x s texture space image space • Per vertex: specify position (x, y, z) and texture coordinates (s, t) • Texture coordinates are interpolated during scan conversion and used to look-up the color. H&B 10-17:629-634

  10. 3D Texture mapping 3D texture mapping: • Texture map is volume (stack of bitmaps): memory intensive • Per vertex (s,t,r) coordinates • Applications: • medical 3D images (plane through scan) • solid materials (wood) H&B 10-17:629-634

  11. Procedural texturing • Instead of using a 1-, 2-, or 3-D image: Define function that returns color dependent on value of s, (s,t) or (s,t,r) • Simple: chessboard • Advanced: wood, marble, etc. H&B 10-17:629-634

  12. Perlin Procedural texturing Images Ken Buckner . H&B 10-17:629-634

  13. OpenGL 1D Texture Mapping 1 First, make sure texture mapping is enabled: glEnable(GL_TEXTURE_1D); Load the 1D texture map: GlTexImage1D(GL_TEXTURE_1D, // here comes a 1D map 0, // 0: not part of larger array GL_RGBA, // we use RGBA colors nTexColors, // the number of colors (use power of 2) 0, // no border GL_RGBA, // order of bytes in color GL_UNSIGNED_BYTE, // components color: unsigned bytes lineTexArray); // array with color values H&B 18-5:587-599

  14. OpenGL 1D Texture Mapping 2 Use the 1D color map during rendering: glBegin(…); glTexCoord1f(0.2); // one coordinate per vertex glVertex3fv(p1); glTexCoord1f(0.8); glVertex3fv(p2); … glEnd(); H&B 18-5:587-599

  15. OpenGL 2D Texture Mapping 1 First, make sure texture mapping is enabled: glEnable(GL_TEXTURE_1D); Load the 2D texture map: GlTexImage2D(GL_TEXTURE_2D, // here comes a 2D map 0, // 0: not part of larger array GL_RGBA, // we use RGBA colors texwidth, // width of texture map (use power of 2) texHeight, // heigth of map (use power of 2) 0, // no border GL_RGBA, // order of bytes in color GL_UNSIGNED_BYTE, // components color: unsigned bytes surfTexArray); // array with color values H&B 18-5:587-599

  16. OpenGL 2D Texture Mapping 2 Use the 2D color map during rendering: glBegin(…); glTexCoord1f(0.2, 0.8); // two coordinates per vertex glVertex3fv(p1); glTexCoord1f(0.8, 0.8); glVertex3fv(p2); … glEnd(); H&B 18-5:587-599

  17. OpenGL texture parameters 1 Generic call: glTexparameter*(target, parameter, value(s)); * = iv or fv target = GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D Some useful parameters: GL_TEXTURE_WRAP_S GL_TEXTURE_WRAP_T GL_TEXTURE_MIN_FILTER GL_TEXTURE_MAG_FILTER H&B 18-5:587-599

  18. OpenGL texture parameters 2 V = GL_REPEAT: Use only fractional part of texture coordinate V = GL_CLAMP: Clamp texture coordinate to [0, 1] range glTexparameteri(GL_TEXTURE_2D, GL_WRAP_S, V); glTexparameteri(GL_TEXTURE_2D, GL_WRAP_T, V); (-1,2) (2,3) (0,1) (1,1) All coordinates: (s,t) texture coordinates (0,0) (1,0) texture map (-1,-1) (2,-1) H&B 18-5:587-599 Quadrilateral

  19. OpenGL texture parameters 3 V = GL_REPEAT: Use only fractional part of texture coordinate V = GL_CLAMP: Clamp texture coordinate to [0, 1] range glTexparameteri(GL_TEXTURE_2D, GL_WRAP_S, V); glTexparameteri(GL_TEXTURE_2D, GL_WRAP_T, V); (-1,2) (2,3) (-1,-1) (2,-1) GL_REPEAT, GL_CLAMP GL_CLAMP, GL_CLAMP GL_REPEAT, GL_REPEAT H&B 18-5:587-599

  20. OpenGL texture parameters 4 glTexparameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, V); glTexparameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, V); Texture Pixel V = GL_NEAREST Texture Pixel V = GL_LINEAR Can be set independently for enlarged textures (MAG_FILTER) and shrunk textures (MIN_FILTER). H&B 18-5:587-599

  21. OpenGL texture color glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, V) V = GL_MODULATE Final color is product of current color and texture color Default value. Using texture on black object has no effect! V = GL_REPLACE Final color is texture color Simplest to use. V = GL_DECAL, GL_BLEND If you want to do something special. H&B 18-5:587-599

  22. OpenGL named textures 1 Multiple textures simultaneously in one scene? Using glTexImage2D multiple times per frame is expensive. Solution: named textures. Initially bind textures to symbolic id’s: myTextureInit(); // Taken care of in template assignment { glBindTexture(GL_TEXTURE_2D, head_texture_id); glTexImage2D(..., head_texture); glBindTexture(GL_TEXTURE_2D, torso_texture_id); glTexImage2D(..., torso_texture); glBindTexture(GL_TEXTURE_2D, bricks_texture_id); glTexImage2D(..., bricks_texture); } H&B 18-5:587-599

  23. OpenGL named textures 2 Multiple textures simultaneously in one scene? Using glTexImage2D multiple times per frame is expensive. Solution: named textures. During drawing: refer to symbolic id’s: myDraw(); { glBindTexture(GL_TEXTURE_2D, head_texture_id); myDrawHead(); glBindTexture(GL_TEXTURE_2D, torso_texture_id); myDrawTorso(); glBindTexture(GL_TEXTURE_2D, bricks_texture_id); myDrawBricks(); } H&B 18-5:587-599

  24. Texture mapping hints Use texture maps with dimensions that are a power of 2 (128128, 128256, 512512, etc.); Try to minimize distortion, i.e., aim at using dimensions in texture space that are proportional to dimensions in world space; Use: glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE); You can use multiple pictures in one texture map, and control via texture coordinates which picture you use. 1 2 3 4 H&B 18-5:587-599

  25. Finally • How about hidden surfaces?

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