Tag: threads

Threading and OpenGL, test 2

Here's a simple test program using LibQGLViewer (screen capture with xvidcap). The vertex array and the index array that OpenGL draws (using glDrawElements) are held in a GLData class which holds a mutex. The Viewer class locks the mutex while drawing, and the worker-thread locks the mutex while updating the data. Here the worker task re-positions the original vertex position, signals the Viewer to draw, and then sleeps for 40 ms. When we don't rotate or zoom with the mouse the frame-rate should thus be 25 Hz. Rotating or zooming causes more frequent re-draws and a higher frame-rate.

To gain any real benefit on a multi-core machine I think the worker thread needs to work on a 'dirty' copy of the data, and we only lock the mutex for a minimal time while swapping in the updated data for the real data. Anyone have any good example code for this? Both a case where the worker produces new data at a slow rate (slower than Viewer re-draws), and at a faster rate should be handled.

Here's an UML(ish) diagram drawn with dia:

Code.

Multithreaded OpenGL with Qt

I've looked at this example from 2003 and converted it to something that compiles with qt4.7. Here: https://github.com/aewallin/sandbox/tree/master/qt_opengl_threads

Each window is a QGLWidget with its own QThread associated with it that does the drawing. That means the UI should stay responsive despite heavy processing in the threads.

I wonder if this can be made to work with libQGLViewer ?


(The screenshot has caught many windows in the middle of a drawing operation. I couldn't get double-buffering to work. In practice it looks very smooth to the eye.)