Texture Resources Texture resources are finite and the amount of available texture varies among implementations  An application may evaluate whether sufficient resources exist glGetIntegerv(GL_MAX_TEXTURE_SIZE, ...) will show the total texture memory Be aware that pixel format will greatly affect texture utilization (as well as mipmaps and borders) A texture proxy is a place holder which allows more accurate queries                     glTexImage2D(GL_PROXY_TEXTURE_2D, 0, GL_RGBA8,                 64, 64, 0,                 GL_RGBA, GL_UNSIGNED_BYTE, NULL);    glGetTexLevelParameteriv(GL_PROXY_TEXTURE_2D, 0,                              GL_TEXTURE_INTERNAL_FORMAT,                             &proxyComponents);    printf ("Proxying 64x64 level 0 RGBA8 texture (level 0)\n");    if (proxyComponents == GL_RGBA8)       printf ("proxy allocation succeeded\n");    else       printf ("proxy allocation failed\n");    Unfortunately proxies to not report existing texture usage.

	Replacing All or Part of a Texture Image Creating an entirely new texture may be more computationally expensive than modifying an existing one    glTexSubImage2D() may be used to replace portions of the texture data  Not restricted to powers of two(!) glCopyTexSubImage2D() in a similar fashion

Using a Texture's Borders Image from http://www.terrex.com/www/netpages/downloadpage.htm Scene with texture requirements larger than graphics hardware can be rendered Texture loads and re-loads must be done per frame Since a single texture map is available at a time (in this scenario) problems can occur at the edges of the image (for blending) Specifying textures which share border pixels will resolve this issue The border values may be used when the texture does not completely cover a primitive (clamping)

Multiple Levels of Detail Objects farther away from the viewpoint will have several texels which may map to a pixel in the framebuffer Causes annoying "texture swimming" Multiple pre-filtered versions of a texture (mipmaps) allow for the appropriate resolution image to be applied to a primitive                  To use mipmapping all sizes of the texture in powers of two must be provided down to 1x1 pixel -- using glTexImage2D()

Filtering Texture maps are rectangular, but there is rarely a one-to-one mapping of texels to pixels in the framebuffer A single pixel can refer to: a fraction of a texel (magnification) a collection of texels (minification) OpenGL allows specification of the filtering options NOTE! This can have a critical effect on the image quality for some applications Some cases result in minification in one axis and magnification in another (avoid this situation) - OpenGL will choose

	Specifying Filtering glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,        GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,        GL_NEAREST);   First parameter is GL_TEXTURE_2D or GL_TEXTURE_1D Second parameters specifies minification or magnification Third specifies one of the following:

Specifiying Filtering (cont) GL_NEAREST - The texel nearest to the center of the pixel is seleted NOTE! this can cause aliasing artifacts GL_LINEAR - a weighted linear average of the 2x2 texels nearest to the center of the pixel NOTE!  the texel coordinates may extend beyond the defined texture - GL_REPEAT or GL_CLAMP (and the border) will affect the result GL_LINEAR produces a "smoother" texturing (this may or may not be good) GL_NEAREST requires less computation

Mipmaps and Filtering Magnification always uses the largest mipmap (level 0) if defined Minification chooses a filter between the appropriate mipmap (or mipmaps) GL_NEAREST_MIPMAP_NEAREST specifies GL_NEAREST for the nearest mipmap GL_LINEAR_MIPMAP_NEAREST specifies GL_LINEAR for the nearest mipmap To interpolate between the nearest two mipmaps: GL_NEAREST_MIPMAP_LINEAR GL_LINEAR_MIPMAP_LINEAR higher quality = more computation

Texture Objects A texture object allows texture data to be stored for later reference Results in performance gains because the texture bind is with existing textures Four steps are required: Generate texture names with glGenTextures() Initially create (a.k.a. bind) the texture objects to the texture data If there is support for a working set, determine if there is sufficient space Bind (and rebind) texture objects as needed

	Homework Compile and execute the texture tutor (homework.tar)    Extra Credit: (yeah, right ...)