Frame stuttering is separate from Screen Tearing, though the two are often used in close proximity to one another. Frame stuttering occurs when the display is anticipating a new frame to be delivered from the GPU, but the GPU misses its mark (processes the frame too slowly), and thus must wait for the next cycle before pushing the new data to the display. When this happens, the display is forced to redraw the previous frame, resulting in two instances of the same piece of information (stuttering). This occurs when V-Sync is enabled.
Because a 60Hz display expects a frame every 16ms, missing that 16ms mark means it must wait for the next cycle (another 16ms). The display has to do something in that time, so it draws the previous frame again. This causes a stutter when the next frame is drawn, given that we're now missing information in between the frames. This mostly applies to V-Sync.
Read more about this in the V-Sync section.
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