Frame Capture and Analysis Tools Reviewccokeman - April 1, 2013
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The ultimate goal here is to measure what the end user sees when playing their favorite games, not what is reported by a software tool; although FRAPS is not at fault for the results it provides as it reads the frames as they are delivered from the game engine. To find the actual number delivered to the display we need to use the hardware and software shown earlier. Part of the problem we have is that the GPU can easily deliver more frames than the monitor can display with a standard 60Hz refresh rate, giving you an imbalance in the rate at which the frames are delivered versus viewed. By measuring what is viewable versus what is measured as the frames leave the game engine we can get a clearer picture of where the issues lie. When frames are delivered but not seen or are on screen for times as short as 20 scan lines they may as well not be counted.
Let's revisit the overlay software part of the FCAT tools for a minute so that the explanation on runts and drops makes more sense. Overlay uses a series of 16 colors in a never changing order. By making the order static it is easy to identify when a frame is dropped as the sequence is then out of order. The order is White, Lime, Blue, Red, Teal, Navy, Green, Aqua, Maroon, Silver, Purple, Olive, Gray, Fuchsia, Yellow, and Orange. As you can see from the sequence of frames below the order runs and repeats when all the frames are sent to the display.
Runts & Drops:
Using the overlay tool included as part of the FCAT toolbox allows the rest of the software to identify each frame to complete the analysis. Since the color pattern is static there is an easy way for the FCAT tools to identify when you have a frame out of sequence or shown for a short period of time leading to both runt and dropped frames. So what is a runt frame and a dropped frame? The definition of a dropped frame is one that was rendered but not displayed on the screen. A runt frame is one that is displayed but is for such a short period of time that it is not seen on screen either. Runt frames are around 20 scan lines or less; at 1920x1080 that makes them small enough that they normally pass fast enough that they are not seen or perceived. Usually, as seen below, a runt is accompanied by some screen tearing. The example on the right has a series of five different frames displayed at one time: one fully formed frame, two partial frames, and a pair of runt frames.
By identifying these frames as ones the user will never experience you can pull them from the metrics measurements and show a more realistic accounting of what the end user will see while gaming. Especially when using dual GPU configurations. Let's take a look at some preliminary results to see what these new metrics will show us.