Here's a video of our test run in Tomb Raider, along with screenshots showing the quality settings used. At these settings, especially with 4X supersampling, this game is intensive enough to stress any of these high-end graphics solutions.
Ok, here's where things get a little complicated. The plots below show frame-by-frame rendering times for each graphics card, as captured with two different tools: Fraps and FCAT. Fraps measures when a frame is finalized by the game engine and handed to the DirectX API, relatively early in the rendering process. Fraps results get us as close as possible to the game engine itself, whose internal simulation timing determines the content of each frame—i.e., where objects are positioned in the game world as they move through time. FCAT analyzes the contents of the screen to tell you exactly when a frame reached the display. Both tools are useful for determining animation smoothness, because an interruption in either frame dispatch or frame delivery can disrupt the illusion of motion.
Fraps and FCAT results tend to correspond pretty closely, generally speaking. They don't correspond exactly here because we weren't able to use both tools at once. The results you're seeing in the plots come from a single test run, conducted manually, with each tool. (We did test three times per tool per card, though, for FPS averages and such.)
The button labeled "HD 7990" will get you results from the Catalyst 13.8 beta with frame pacing disabled, and the button labeled "HD 7990 paced" will show you how frame pacing changes things. Flip back and forth between them, and you can see a dramatic difference. Without pacing, the 7990's results from Fraps and FCAT both are all over the map. Look at the zoomed-in plots below the main one, and you can see the telltale see-saw pattern that comes from microstuttering. The pattern is very pronounced, too, with frame-to-frame intervals ranging from three to 40 milliseconds and back again.
With pacing enabled, the 7990's Fraps results still have an intermittent high-low latency pattern, but it's not a constant problem. The FCAT plot becomes much, much smoother. Tomb Raider appears to advance its simulation time using a moving average or some sort of set interval, rather than simply sampling the current frame time. We've found that those relatively small (typically under 40 ms) intermittent variations in the Fraps plots don't translate into perceptible hiccups or slowdowns. Since the game works that way, I'd give more weight to the FCAT results in the charts below.
If you only care about FPS averages, then the good news here is that frame pacing doesn't appear to reduce the number of frames rendered over time. If you care about smooth gaming, then the latency-oriented 99th percentile frame time may be the more helpful metric. Frame pacing vaults the Radeon HD 7990 from the middle of the pack to the front ranks, just ahead of its direct rival, the GeForce GTX 690.
Here's a look at the entire frame latency curve. As you can see, without pacing, the 7990's curves from both Fraps and FCAT start out low and escalate steadily, matching or crossing the curves from a single 7970. With pacing enabled, the 7990's latency curves are flatter, and frame times are dramatically lower in the right half of the plot. That avoidance of high-latency frames should translate into smoother animation, so the frame-paced results are much more desirable.
We can look at the amount of time spent working on high-latency frames in order to get a sense of the "badness" in each card's performance. The more time spent on high-latency frames, the more likely you are to notice a problem. For Tomb Raider, we can ratchet our threshold of badness down to 33 milliseconds, the equivalent of 30 FPS or two display refresh intervals on a 60Hz monitor, and the 7990 with frame pacing still aces the test. FCAT tells us the 7990 with pacing only spends two milliseconds beyond the 33-ms threshold. That's pretty fluid.
Those are the numbers, and hopefully you have a sense of what they mean. The impact of frame pacing is palpable. When testing this driver, I first played each game with frame pacing enabled, and then I disabled pacing and played the same section again. The difference in the smoothness of the animation was comical. I laughed. With frame pacing, the 7990 delivered a nicely playable experience. Going without pacing after having used it was painful—easily slower and chunkier.
Since we capture each and every frame during our FCAT testing, we can convey a sense of the experience with some videos. I've slowed things down to half speed, from 60Hz to 30Hz, so the differences between the solutions should be even more evident. Please do realize we're using YouTube here, so it's kind of like filtering espresso through a sock, but I'm hoping you at least get some of the flavor. Ignore the trippy overlay colors, which are used by FCAT to mark each frame. Watch for things like the fluidity of the ground passing under Laura or the motion of her arms and hair, and I think you'll notice the gap in fluidity.
First, here's a side-by-side video showing the impact of frame pacing:
Here's just the 7990 without frame pacing:
Here it is with frame pacing:
And now the GeForce GTX 690:
My hope is that these videos illustrate what we're talking about reasonably well. See what you think.
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