OpenGL Notes 3 - Textures

Following is the relevant OpenGL functions that involved in implementing textures related functionality.

OpenGL Functions Purpose
glTexParameter() Configure relevant texture’s parameters option
glGenTextures() Create texture object(s)
glBindTexture() Bind texture object for subsequent OpenGL operations
glTexImage2D() Specify texture data for speicify mipmap level
glGenerateMipmap() Generate full-chain of mipmap for all mipmap levels
glVertexAttribPointer() Define a generic vertex attribute data
glEnableVertexAttribArray() Enable vertex attrib array
glActiveTexture() Set texture object to be active

Intersting notes are as follows (with relevant topic prefixed for each one)

Topic Note
Misc We can directly specify vertices’ position in NDC space so no further transformation should be done in vertex shader; thus it just passes through the information to next stage.
Misc Texture filtering GL_NEAREST select which pixel’s center is closest to the texture coordinate, but GL_LINEAR (or bilinear filtering) will take interpolated values from texture coordinates of nearby texels then use them to calculate mixed color of final pixel color
Mipmap Mipmapping operation to select which pixels to show on screen will happen when there is minifying (zoom-out). You can check this on man page of glTexParameter() and check its GL_TEXTURE_MIN_FILTER which has available values related to mipmap, but not for GL_TEXTURE_MAG_FILTER.
Mipmap When creating texture object, users can manually set which mipmap level should be based and its quality level via glTexParameter() for its GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MIN_LOD and GL_TEXTURE_MAX_LOD.
Mipmap Users have option to load all mipmap-level data from texture i.e. DDS texture, or let OpenGL automatically generates via glGenerateMipmap()
Shader As per Explicit uniform location section here we cannot define uniform variable with the same location at multiple location in different stage of shader i.e. both at vertex and fragment shader even though they both have the same type and name. This makes it more difficult to work with in case of explicit defining uniform location. Solution is to define its location at one place, then duplicate its definition without location but with same type and name in other shader stages.
Misc Use glActiveTexture() as needed especially when users need to deal with multiple textures setup in shader. This is to let OpenGL knows which current active texture object for subsequent OpenGL operations it will be working with.


First published on Aug, 16, 2019

Written by Wasin Thonkaew
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