As of version 6.11, Ren'Py will take advantage of OpenGL display hardware, if it's present and functional. Using OpenGL brings with it several advantages, such as allowing vertical-blank synchronization and scaling games to full-screen size while preserving aspect ratio.
On startup, Ren'Py will attempt to determine if the computer has an OpenGL implementation that supports the features Ren'Py needs. It will then test that OpenGL performance is sufficient to run Ren'Py games.
If both tests pass, Ren'Py will continue in OpenGL mode. Otherwise, it will revert to software rendering, a slower and less functional form of rendering.
The best way to check if Ren'Py is using OpenGL rendering is to try to resize the Ren'Py window. If the window can be resized, it's using OpenGL support. If not, software rendering is being used.
A small fraction of systems may experience problems when running OpenGL-accelerated Ren'Py games. These problems are often due to buggy graphics drivers, and so your first step to fixing them should be to check for an update to your graphics card drivers.
If upgrading your video drivers does not fix the problem, you should disable OpenGL support. To disable OpenGL support:
This method does not work on Mac OS X. To disable OpenGL support there, download this environment.txt file, and place it in the directory with the .app file used to start Ren'Py.