X Configuration

IVL draws images from the bottom to the top of a window. This is known as the rasterization order. (The OpenGL standard does not dictate a specific rasterization order, but does dictate that the image data coordinate system has it's origin at the lower left corner of an image. This coordinate system lends itself naturally to a bottom to top rasterization.) This differs from the frame buffer, which refreshes from the top to the bottom of the screen. Because of this, you may see a tearing effect as your image is being drawn. To hide this artifact of the rasterization order, you can use hardware double-buffering on those devices that support it (see glXSwapBuffers).

When you do this, you may still see some minor tearing due to buffer swapping. This is a less severe artifact than the one described above. You can eliminate this secondary tearing by forcing the X Server to swap hardware buffers during the vertical retrace interval. To do this, add the following to your X*screens file:

   Screen /dev/crt

       ScreenOptions

           SwapBuffersOnVBlank

Note: since this affects hardware buffers only, it will have no effect on graphics systems that do not support hardware double-buffering. Also, synchronizing with vertical retrace may cause a slight decrease in performance.

With Single Logical Screen (SLS), the X11 server manages multiple physical display devices as if they were a single frame buffer. Thus the use of the term "logical".

The initial release of IVL does not support the Single Logical Screen environment. This includes the case where IVL renders to a drawable that resides on a single physical display (frame buffer). To reiterate, SLS is not supported.

However, IVL is supported on multi-display configurations that are not configured as a Single Logical Screen.