Agocs: Boosting performance with shader binary caching in Qt 5.9

Laszlo Agocs takesa look at improvements to the basic OpenGL enablers that form thefoundation of Qt Quick and the optional OpenGL-based rendering path ofQPainter in Qt 5.9. "Asexplained here, such shader programs will attempt to cache the programbinaries on disk using GL_ARB_get_program_binaryor the standard equivalents in OpenGL ES 3.0. When no support is providedby the driver, the behavior is equivalent to the non-cached case. The filesare stored in the global or per-process cache location, whichever is writable. The result is a nice boost in performance when a program is created with the same shader sources next time."