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What is the theoretical concept of VSync, and how does it affect rendering?

Tiskolin
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Ankush
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2 Answers2

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Monitors refresh pixels in various ways, but they're not all updated at the same time. Old screens for example, used to refresh the pixels one line at a time, top to bottom.

The problem occurred if it was halfway down the screen when it got the new image and simply continued with that. You then had the top half of the screen using the previous frame, while the bottom half of the screen was using the new frame. VSync prevents this by making sure updates are made between refreshes, not during.

This isn't really a problem any longer with modern screens.

If you'd like to read up on VSync here's some helpful wikipedia articles: http://en.wikipedia.org/wiki/Vertical_synchronization and http://en.wikipedia.org/wiki/Screen_tearing

Steven Mills
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  • You explain vSync very well, but i still have no idea what `QualitySettings.vSyncCount` does, if it were a Boolean it would obviously toggle vSync on or off, but it is an integer so that means that whoever wrote it likely intended for more than two different values to be set (so not just on/off). Please consider updating your answer. – x13 May 16 '19 at 11:13
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Taken from the documentation of unity3D

Rendering can be synchronised with the refresh rate of the display device to avoid "tearing" artifacts. You can choose to synchronise with every vertical blank (VBlank), every second vertical blank or not to synchronise at all.

sebastian s.
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    what is VBlanck ? can you elaborate it more. – Ankush Jan 18 '14 at 14:46
  • Well, its a term from the early days of display technology. It's the time between the last element of a frame or field of a display, and the beginning of the first line of the following frame. – sebastian s. Jan 18 '14 at 14:49
  • In the vblank time the display registers get written with the new data for each line/pixel. This needed some time in the earlier days, its as fast as "no time" with new displays. – sebastian s. Jan 18 '14 at 15:00
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    All this has a lot to do with display refreshrate versus frames per seconds from graphics cards – sebastian s. Jan 18 '14 at 15:03