OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Retrieving Texture Data

Once you have a texture containing data, it is possible to read that data either back into your application’s memory or back into a buffer object. The function for reading image data from a texture is glGetTexImage(), whose prototype is as follows:

void glGetTexImage(GLenum target, GLint lod, GLenum format,                         GLenum type, GLvoid* image);

Retrieves a texture image from the texture bound to target. target must be one of GL_TEXTURE_1D, GL_TEXTURE_2D, GL_TEXTURE_3D, GL_TEXTURE_1D_ARRAY, GL_TEXTURE_2D_ARRAY, GL_TEXTURE_CUBE_MAP_ARRAY, or GL_TEXTURE_RECTANGLE. Additionally, the targets GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X, GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, ...