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ISSUE 230 IT CAN’T RAIN ALL THE TIME

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THERE’S MORE…Gigabyte: behind the scenesCore i5 specs revealedReal Time Strategy classics!

Intel: still the performance king?Intel: still the performance king?

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62 September 2009

are two core issues at stake here, rendering smoothness and the integrity of individual frames. As most people know, feature fi lms are generally displayed at around 24 frames per second, a fi gure that’s apparently enough for smooth motion. And yet experienced gamers will also know that a PC can somehow spew out much higher in-game frame rates without the same impression of seamless motion.

At the same time, most PC gamers will have noticed a phenomenon commonly known as tearing. In simple terms, tearing occurs when frames are

Frantic fragging demands fast frame rates. That’s one of the central tenets of PC gaming, right? Attempting to rail gun the

opposition between the peepers as you artfully jump-strafe through the air doesn’t really fl y if your PC is dropping frames like a pathological litterbug, that’s for sure.

However, peak frame-rate performance is only part of the problem. The order and manner in which the individual image frames appear on your screen also matters. Enter, therefore, the concept of frame buffering. There

Bump up the bufferingForget maxing out your frame rates or enabling VSync. For silky smooth gaming you need to bump up your graphics buffer

sent to the monitor out of sync with its refresh rate. Consequently, slithers of two separate frames are displayed simultaneously. During fast paced action, it can result in a visually jarring horizontal line as if the screen had been sliced in two and the pieces dragged in opposite directions.

One solution is VSync, which co-ordinates the output of the graphics with the monitor refresh. It’s great if you have spare performance but can do horrible things to your frame rates if you don’t. But don’t despair, there’s another option: triple buffering. ¤ Jeremy Laird

Above Fast-paced action can result in visually jarring horizontal lines

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September 2009 63

Bump up the buffering

By default, a PC’s graphics subsystem has two image or frame buffers, a back buffer and a front buffer. The back buffer is the initial recipient of and storage receptacle for new frames produced by the graphics card, meanwhile the front buffer is being drawn on the PC monitor. In order to display a new frame, the status of the two buffers is ‘swapped’ following which another new frame is drawn to the back buffer and the process is repeated (1).

The problem with this method is that it’s driven by the frame rate production of the graphics card. If that is higher than the refresh rate of the monitor (typically 60Hz for current LCD panels), the buffers will occasionally get swapped before a frame has completed transmission from the front buffer to the screen. When that happens, part of the previous frame is retained and a composite image is rendered. Welcome to screen tearing (2).

The most common solution to this problem is to synchronise buffer swapping with the monitor’s refresh rate. Only when the monitor is ready for a new frame are the buffers swapped. This works well when a graphics card is rendering more than 60 frames. However, drop even slightly below that rate and the system is forced to repeat

frames to keep the synchronisation in tact. This in turn means the buffers must wait for the next refresh cycle to swap and the result is performance capped at 30 frames per second. Drop below 30 frames and things can get really ugly. VSync, therefore, is hardly the perfect solution.

But there is an alternative to using VSync: triple buffering. As the name suggests, triple buffering adds another buffer to smooth out the rendering process. This allows the graphics card to constantly render to a pair of back buffers leaving the front buffer to essentially pinch the most recent complete frame available once every monitor refresh cycle (3)).

Fortunately, enabling triple buffering is pretty straightforward; you’ll fi nd it in the graphics options of some games. For everything else, you’ll need a third party tool that includes triple buffer override option (4).

Just such a tool is RivaTuner 2.0, which includes a secondary utility known as D3DOverider. Note that this application only works for DirectX games, not OpenGL. But in this day and age, that’s really most of ‘em. So that’s it. No stuttering, no tearing, no loss in performance. Just silky, silky smooth rendering. Enjoy.

How to stop screen tearing

Bump up the buffering

3

4

Technical analysisBenchmarking buffering methods presents a conundrum. The fastest raw frame rates are produced by standard double buffering. Enable VSync and at best you’ll see 60 frames per second. However, should the underlying capability of your graphics card drop below 60 frames per second, the result is a dive in performance to no more than 30. Triple buffering also reduces the raw frame rate, because only the rendered frames are counted, not those circulating in the pair of back buffers. However, unlike VSync it does allow you to make the most of performance in the 30 to 60 frames per second range.

RivaTuner 2.0 includes a triple buffer override option

Triple buffering smooths out the rendering process

2

Welcome to screen tearing. It’s really, really annoying isn’t it?

1

Your card’s frame production needs to match your screen’s refresh rate

PCF230.overclocking 63 16/7/09 8:21:43 am