This information is valid for PyMOL v1.4.0. Please see PyMOL Rendering Engine Improvements for later builds.
OpenGL shaders are a different way to render images. Instead of using the fixed pipeline of GL-based light models and effects, the lights and effects can be customized on the video card. This yields increases in rendering speed and allows for a great variety of effects.
PyMOL v1.4.0 and prior currently has shaders disabled by default. To turn on shaders
set use_shaders, 1 # global shader settingset cartoons_use_shader, 1 # per representation settingset sticks_use_shader, 1 # per representation settingset surface_use_shader, 1 # per representation settingset ribbon_use_shader, 1 # per representation settingset sphere_mode, 9 (ARB) or set sphere_mode, 5 (GLSL)