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Pemetaan Tekstur

Pemetaan Tekstur. Outline. Memetakan tekstur ke permukaan datar Contoh-contoh dengan OpenGL Pemetaan ‘Bump’ MIPMAPS. Texture Mapping. Limited ability to generate complex surfaces with geometry Images can convey the illusion of geometry

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Pemetaan Tekstur

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  1. Pemetaan Tekstur Pemetaan Tekstur

  2. Outline • Memetakan tekstur ke permukaan datar • Contoh-contoh dengan OpenGL • Pemetaan ‘Bump’ • MIPMAPS Pemetaan Tekstur

  3. Texture Mapping • Limited ability to generate complex surfaces with geometry • Images can convey the illusion of geometry • Images painted onto polygons is called texture mapping Pemetaan Tekstur

  4. Texture Maps • Images applied to polygons to enhance the visual effect of a scene • Rectangular arrays of data • Color, luminance, alpha • Components of array called texels • We’ve also had volumetric voxels Pemetaan Tekstur

  5. T V S U Texture Mapping • Texture map is an image, two-dimensional array of color values (texels) • Texels are specified by texture’s (u,v) space • At each screen pixel, texel can be used to substitute a polygon’s surface property (color) • We must map (u,v) space to polygon’s (s, t) space Pemetaan Tekstur

  6. Texture Mapping • (u,v) to (s,t) mapping can be explicitly set at vertices by storing texture coordinates with each vertex • How do we compute (u,v) to (s,t) mapping for points in between • Watch for aliasing • Watch for many to one mappings • Watch for perspective foreshortening effects and linear interpolation Pemetaan Tekstur

  7. Example Texture Map Applied to tilted polygon Pemetaan Tekstur

  8. Example Texture Map glVertex3d (s, s, s) glTexCoord2d(1,1); glVertex3d (-s, -s, -s) glTexCoord2d(1,1); Pemetaan Tekstur

  9. Example Texture Map glVertex3d (s, s, s) glTexCoord2d(5, 5); glVertex3d (s, s, s) glTexCoord2d(1, 1); Pemetaan Tekstur

  10. Texture Coordinates • Every polygon has object coordinates and texture coordinates • Object coordinates describe where polygon vertices are on the screen • Texture coordinates describe texel coordinates of each vertex (usually 0 -> 1) • Texture coordinates are interpolated along vertex-vertex edges • glTexCoord{1234}{sifd}(TYPE coords) Pemetaan Tekstur

  11. Textures • Texture Object • An OpenGL data type that keeps textures resident in memory and provides identifiers to easily access them • Provides efficiency gains over having to repeatedly load and reload a texture • You can prioritize textures to keep in memory • OpenGL uses least recently used (LRU) if no priority is assigned Pemetaan Tekstur

  12. Example use of Texture • Read .bmp from file • Use Image data type • getc() and fseek() to read image x & y size • fread() fills the Image->data memory with actual red/green/blue values from .bmp • Note • malloc() Image->data to appropriate size • .bmp stores color in bgr order and we convert to rgb order Pemetaan Tekstur

  13. Step 2 – create Texture Objects • glGenTextures(1, &texture[texture_num]); • First argument tells GL how many Texture Objects to create • Second argument is a pointer to the place where OpenGL will store the names (unsigned integers) of the Texture Objects it creates • texture[] is of type GLuint Pemetaan Tekstur

  14. Step 3 – Specify which texture object is about to be defined • Tell OpenGL that you are going to define the specifics of the Texture Object it created • glBindTexture(GL_TEXTURE_2D, texture[texture_num]); • Textures can be 1D and 3D as well Pemetaan Tekstur

  15. Step 4 – Begin defining texture • glTexParameter() • Sets various parameters that control how a texture is treated as it’s applied to a fragment or stored in a texture object • // scale linearly when image bigger than texture glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); • // scale linearly when image smaller than texture glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); Pemetaan Tekstur

  16. Step 5 – Assign image data • glTexImage2D(); Pemetaan Tekstur

  17. glTexImage2D – Arg 1 • GLenum target • GL_TEXTURE_2D • GL_PROXY_TEXTURE_2D • Provides queries for texture resources • Proceed with hypothetical texture use (GL won’t apply the texture) • After query, call GLGetTexLevelParamter to verify presence of required system components • Doesn’t check possibility of multiple texture interference Pemetaan Tekstur

  18. glTexImage2D – Arg 2 • GLint level • Used for Level of Detail (LOD) • LOD stores multiple versions of texture that can be used at runtime (set of sizes) • Runtime algorithms select appropriate version of texture • Pixel size of polygon used to select best texture • Eliminates need for error-prone filtering algorithms Pemetaan Tekstur

  19. glTexImage2D – Arg 3 • GLint internalFormat • Describes which of R, G, B, and A are used in internal representation of texels • Provides control over things texture can do • High bit depth alpha blending • High bit depth intensity mapping • General purpose RGB • GL doesn’t guarantee all options are available on given hardware Pemetaan Tekstur

  20. glTexImage2D – Args 4-6 • GLsizei width • GLsizei height • Dimensions of texture image • Must be 2m + 2b (b=0 or 1 depending on border) • min, 64 x 64 • GLint border • Width of border (1 or 0) • Border allows linear blending between overlapping textures • Useful when manually tiling textures Pemetaan Tekstur

  21. glTexImage2D – Args 7 & 8 • GLenum format • Describe how texture data is stored in input array • GL_RGB, GL_RGBA, GL_BLUE… • GLenum type • Data size of array components • GL_SHORT, GL_BYTE, GL_INT… Pemetaan Tekstur

  22. glTexImage2D – Arg 9 • Const GLvoid *texels • Pointer to data describing texture map Pemetaan Tekstur

  23. Step 6 – Apply texture • Before defining geometry • glEnable(GL_TEXTURE_2D); • glBindTexture(GL_TEXTURE_2D, texture[0]); • glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE); Pemetaan Tekstur

  24. glTexEnv() First argument to function is always GL_TEXTURE_ENV Pemetaan Tekstur

  25. gluScaleImage() • Alters the size of an image to meet the 2m size requirement of OpenGL • Scaling performed by linear and box filtering glCopyTexImage2D() • Use current frame buffer contents as texture • Copy frame buffer to named texture location Pemetaan Tekstur

  26. glTexSubImage2D() • Replace a region of current working texture with a smaller texture • SubImage need not adhere to 2m size limitation • This is how you add data from your system’s camera to GL environment • glCopyTexSubImage2D • Frame buffer cut and paste possible too Pemetaan Tekstur

  27. Bump Mapping • Use textures to modify surface geometry • Use texel values to modify surface normals of polygon • Texel values correspond to height field • Height field models a rough surface • Partial derivative of bump map specifies change to surface normal Pemetaan Tekstur

  28. Bump Mapping Pemetaan Tekstur

  29. Displacement Mapping • Bump mapped normals are inconsistent with actual geometry. Problems arise (shadows). • Displacement mapping actually affects the surface geometry Pemetaan Tekstur

  30. Mipmaps • multum in parvo -- many things in a small place • A texture LOD technique • Prespecify a series of prefiltered texture maps of decreasing resolutions • Requires more texture storage • Eliminates shimmering and flashing as objects move Pemetaan Tekstur

  31. MIPMAPS • With versus without MIPMAP Pemetaan Tekstur

  32. MIPMAPS • Arrange different versions into one block of memory Pemetaan Tekstur

  33. gluBuild2DMipmaps • Automatically constructs a family of textures from original texture size down to 1x1 Pemetaan Tekstur

  34. Advanced Mipmaps • You can specify additional mipmap levels on the fly • MIN_LOD may reduce popping • MAX_LOD may reduce over compression • You can specify min mipmap level • Useful for mosaicing (Alphabet on a texture) Pemetaan Tekstur

  35. Referensi • 1: , 4:GraphicsSlides07.pdf , 9:Lecture14 • Buku Teks : • F.S.Hill, Jr., COMPUTER GRAPHICS – Using Open GL, Second Edition, Prentice Hall, 2001 • Foley, van Dam, Feiner, Hughes, and Philips, Introduction to Computer Graphics, Addison Wesley, 2000 • Lecture Notes / Slide-Presentation / Referensi lain yang diperoleh melalui internet : • Andries van Dam, Introduction to Computer Graphics, Slide-Presentation, Brown University, 2003, (folder : brownUni) • _______________, Interactive Computer Graphic, Slide-Presentation, (folder : Lect_IC_AC_UK) • ­­­­­­­­­­­­­­­­­­­­­Michael McCool, CS 488/688 :Introduction to Computer Graphics, Lecture Notes, University of Waterloo, 2003 (lecturenotes.pdf) • _______________, Computer Science 559, Slide-Presentation, Wisconsin University,(folder : Lect_Wisc_EDU) • http://graphics.lcs.mit.edu/classses/6.837/F98/Lecture4/Slide23.html , Slide-Presentation, MIT, (folder : MIT_CourseNote) • _______________, CS 319 : Advance Topic in Computer Graphics, Slide-Presentation, (folder : uiuc_cs) • _______________, CS 445/645 : Introduction to Computer Graphics, Slide-Presentation, (folder :COMP_GRAFIK) • Gladimir V.G. Baranoski, CS 488 : Introduction to Computer Graphics , Waterloo University • Prof. Peter Panfilov , http://cse.yeditepe.edu.tr/~osertel/courses/CSE484/index.html • http://www.cl.cam.ac.uk/Teaching/1998/AGraphics/l3a.html Pemetaan Tekstur

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