Optionally using the X11 paint engine as intemediate step for creating textures

[uwerat]

Using QPainter for creating textures is currently possible by drawing with the OpenGL paint engine to a FBO or by using the Raster paint engine ( better quality ).

But since Qt 5.10 the X11 paint engine has returned and offers a hardware accelerated + good quality backend for QPainter. It needs to be checked if it is possible to use this path.