Examine the image below. Is it an example of what a frame with tearing will look like. Notice the two horizontal cuts across the frame:



    Image courtesy of Wikipedia

    Tearing occurs when a display refreshes its image out of sync with when the graphics card renders its image. The result is part of the image being from the previous frame, and part of it being from the next frame. On slow moving content, this can sometimes be hard to notice, but once there is any sort of motion in the content, tearing becomes incredibly distracting.

    Tearing is a complex issue to solve, but there are a few preventative measures that can be taken to avoid it. The first is to use a professional graphics card, such as something from the nVidia Quadro series. Most companies will not guarantee tear-free playback on anything but their professional cards.

    The second is to always ensure that the displays are identical. Identical can’t be stressed enough. If there is an installation with 3 outputs that have a refresh rate of 60hz, and one output with a refresh rate of 59hz, there is a chance there will be tearing. If there is an installation with two 1080p projectors, and two SXGA+ projectors, there is a chance there will be tearing. The best practice is to use displays that are not only identical in specifications, but are also the exact same model of displays. Network remote access applications like VNC and LogMeIn have also been the culprits of tearing.

    This brings up a very important issue with tearing: there are no hard and fast rules. Sometimes, setups with a handful of different resolutions and refresh rates will work perfectly and won’t tear. On the other hand, sometimes even setups with identical displays can tear. Enough emphasis cannot be put on preventative measures to avoiding tearing. When tearing issues arise, the only things that can be done are a step by step breakdown and analysis of the system to see what is causing the tearing.

    Generally the steps to begin with are as follows, in no particular order:

    • Verify the project isn’t dropping any frames. Dropped frames can sometimes trigger tearing

    • Verify no other applications are interrupting or mirroring the graphics card drivers, such as VNC and LogMeIn.

    • Verify all displays are configured to the same resolution, colour bit depth, and refresh rate, in the nVidia or AMD control panel

    • Verify that none of the displays have any rotation applied in Windows. this can cause unpredictable behaviour.

    • Check for drivers or firmware updates on external video splitters - such as the Datapath X4 or Matrox TripleHead2Go

    • Confirm only 1 Window COMP is being rendered

    • Configure a Premium Mosaic using the nVidia Control Panel to create a single logical display

    There are many instances in which a system that performs perfectly, and doesn’t drop a single frame, will occasionally stutter. This may occur because of how displays and graphics cards negotiate different refresh rates.

    If a project is running at 30 FPS, but a display’s refresh rate is 60hz, frame doubling has to be negotiated somewhere. Between the graphics card and the display, most of the time this negotiation is done transparently, but sometimes there can be issues. What can occur is that instead of negotiating a proper frame doubling for every frame, one frame might be displayed once, while the next frame is displayed for three frames. From the project’s point of view, no time is lost and no frames were dropped, so it would not be reported in the Performance Monitor or Windows Task Manager.