Option "AddARGBGLXVisuals" "boolean"
Adds a 32-bit ARGB visual for each supported OpenGL configuration. This allows applications to use OpenGL to render with alpha transparency into 32-bit windows and pixmaps. This option requires the Composite extension. ENABLE AT YOUR OWN RISK. Some OpenGL applications may display incorrectly when this setting is enabled. Default: No visuals are added.
this is what nvidia says regarding this option
Option "AddARGBGLXVisuals" "boolean"
Adds a 32-bit ARGB visual for each supported OpenGL configuration. This allows applications to use OpenGL to render with alpha transparency into 32-bit windows and pixmaps. This option requires the Composite extension. ENABLE AT YOUR OWN RISK. Some OpenGL applications may display incorrectly when this setting is enabled. Default: No visuals are added.