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Texture

Learn to generate, load, and manipulate textures for parametric surfaces and solid meshes using OpenGL techniques. This guide covers texture format, loading methods, and filtering options for optimal rendering. Get hands-on practice with code examples and troubleshooting strategies.

ljessica
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Texture

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  1. Texture generating textures using textures repeating clamping filtering texturing a parametric surface

  2. Examples of texturing

  3. loadTextures.cpp

  4. where to put the Textures folder • VS: usually in the same folder as the .cpp file. If project is graphics, then in folder graphics/graphics • Xcode: XCodeHowTo link. (class 1) • Unix: in file with executable

  5. Try it now. • First try • loadTextures.cpp from the 1st edition • If the computer complains about glext, just comment out that include in the code. • If you get a white square, call me over. • More errors, see the next two slides, only if I tell you to!

  6. fixing getbmp.cpp • Get the files getbmp.cpp and getbmp.h from the lecture page • in getbmp.cpp, in getbmp.cpp comment out old return and replace with new return: //return bmpRGBA; //mjb return bmpRGB;

  7. fixing loadTextures.cpp • in loadTextures.cpp • comment out the Bitmap struct • comment out the function BitMapFile *getBMPData(string filename) • comment out the function call //image[0] = getBMPData("Textures/launch.bmp"); • and replace with the function call image[0] = getbmp("Textures/launch.bmp");

  8. Format of Texture Big 1-D array: R G B A R G B A R G B A 1st pixel 3rd pixel 2nd pixel

  9. This data is in many photos, but has to be properly retrieved

  10. Book examples use uncom-pressed 24 bit BMP www.tinaja.com/glib/expbmp.pdf

  11. useful function to read texture data from a .BMPFrom 1st edition // Routine to read a bitmap file. // Works only for uncompressed bmp files of 24-bit color. BitMapFile *getBMPData(string filename) • Go through the function • notice BGR vs RGB

  12. If you can't get this version working, there is a new version, with a separate .h and .cpp file, from the 2nd edition. • Links are on the webpage, only if you need it.

  13. Changes to make to loadTextures.cpp from 2nd edition //image[0] = getbmp("../../Textures/launch.bmp"); //mjb image[0] = getbmp("Textures/launch.bmp");

  14. Changes to make to loadTextures.cpp from 2nd edition In main, comment out: glutInitContextVersion(4, 3); glutInitContextProfile(GLUT_COMPATIBILITY_PROFILE); glewExperimental = GL_TRUE; glewInit();

  15. globals and setup staticunsignedint texture[2]; // Array of texture indices. // Create texture index array. glGenTextures(2, texture); // Struct of bitmap file. struct BitMapFile{ int sizeX; int sizeY; unsignedchar *data;};

  16. loadExternalTextures() // Local storage for bmp image data. BitMapFile *image[1]; // Load the texture. image[0] = getBMPData("Textures/launch.bmp"); // Activate texture index texture[0]. glBindTexture(GL_TEXTURE_2D, texture[0]); ... // Specify an image as the texture to be bound with the currently active texture index. glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, image[0]->sizeX, image[0]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, image[0]->data);

  17. loadProceduralTextures() // Activate texture index texture[1]. glBindTexture(GL_TEXTURE_2D, texture[1]); ... • // Specify an image as the texture to be bound with the currently active texture index. glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 64, 64, 0, GL_RGB, GL_UNSIGNED_BYTE, chessboard);

  18. createChessboard(void) • look at function

  19. texture space • texel : pixel of a texture • note: s, t, intervals [0,1]

  20. mapping a polygon to texture space // Map the texture onto a square polygon. glBegin(GL_POLYGON); glTexCoord2f(0.0, 0.0); glVertex3f(-10.0, -10.0, 0.0); glTexCoord2f(1.0, 0.0); glVertex3f(10.0, -10.0, 0.0); glTexCoord2f(1.0, 1.0); glVertex3f(10.0, 10.0, 0.0); glTexCoord2f(0.0, 1.0); glVertex3f(-10.0, 10.0, 0.0); glEnd(); • Interpolate

  21. other texture maps

  22. interpolates through triangles

  23. repeating

  24. repeating

  25. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,GL_REPEAT);

  26. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_CLAMP); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,GL_REPEAT);

  27. fieldAndSky.cpp • run • notice shimmer • try clamping grass in T direction • do graph paper experiment.

  28. Problem with Pixels

  29. GL_NEAREST glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_NEAREST);

  30. GL_LINEAR glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR); • Average the surrounding points

  31. mipmap • make other versions of texture, various sizes • speed vs storage • book has good examples • if you try mipmaplevels.cpp change to d+=10.0 (not .2, also for -=) Nothing happens till box gets very small

  32. fieldAndSkyFiltered.cpp • run and observe differences

  33. texturing parametrized surfaces

  34. texturedTorus.cpp • run • note code for parametrization • // Specify how texture values combine with current surface color values. glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE); • run also DoubletexturedTorusMJB.cpp

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