Javadoc
Toggles the use of the GL_ARB_texture_rectangle extension by the
TextureIO classes. By default, on hardware supporting this
extension, the TextureIO classes may use the
GL_ARB_texture_rectangle extension for non-power-of-two
textures. (If the hardware supports the
GL_ARB_texture_non_power_of_two extension, that one is
preferred.) In some situations, for example when writing
shaders, it is advantageous to force the texture target to
always be GL_TEXTURE_2D in order to have one version of the
shader, even at the expense of texture memory in the case where
NPOT textures are not supported. This method allows the use of
the GL_ARB_texture_rectangle extension to be turned off globally
for this purpose. The default is that the use of the extension
is enabled.