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Serious Statistics Pt. 2: The Sync Encounter

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Fullscreen – Frame Rate Limiter:

At its most basic, the idea behind vertical sync is to have the rate frames are rendered match the rate they are scanned out to the display. With double and triple buffering, this is achieved by ensuring there is a complete frame that can be scanned out to match the display, but by buffering a frame there is going to be some delay between it being rendered and displayed (exactly what we are looking at). By just rendering at the display's refresh rate, synchronization can be achieved without introducing this same latency, and that is the purpose of frame rate limiters, assuming you are able to render faster than the refresh rate.

Completely unsurprisingly, the frame time graphs will just show a line along the 16.667 ms mark.

 

 

 

 

 

GTX 1080 - DX11

GTX 1080 - Vulkan

Vega 64 - DX11

Vega 64 - Vulkan

 

Interestingly the display time graphs do not show just a flat line as there were apparently moments the frames were displayed just above or below 16.667 ms, at least for DirectX 11. My interpretation of this would be the limiter is not perfect, so there are times the frame rate went to 59 FPS or 61 FPS for just long enough to cascade into the display time shifting.

When running under Vulkan, these deviations did not occur, so it would seem there is better or easier control of the frame rate here.

GTX 1080 - DX11

GTX 1080 - Vulkan

Vega 64 - DX11

Vega 64 - Vulkan

 

Looking at the frequency plots for DirectX 11 we see two humps next to the spike around one-frame-later.

GTX 1080 - DX11

GTX 1080 - Vulkan

Vega 64 - DX11

Vega 64 - Vulkan

 

Last but not least here are the latency graphs, which are just flat lines. This makes sense as the frames should just be rendered to the front buffer and then scanned out as soon as is possible.

GTX 1080 - DX11

GTX 1080 - Vulkan

Vega 64 - DX11

Vega 64 - Vulkan

 

One quick note about the frame rate limiter is that while it can minimize screen tearing, it is not guaranteed to prevent it. I did observe some screen tearing, and it seemed to move up or down the screen depending on how I moved, because the tear seemingly synchronized with the display. It would not last for long, but it would occur.

The frame rate limiter is the last of the in-game technologies I tested, as I did not try combining it with v-sync or triple buffering. All that remain are some out-game technologies, and I am going to start with the Desktop Window Manager double buffer, which is as simple to access as playing in a borderless window.




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