Why is there still screen tearing even when fps are limited to be equal to monitor refresh rate? Also if tearing occurs because of fps higher than screen refresh rate why don't games limit fps to be equal to the screen refresh rate by default?
Why is there still screen tearing even when fps are limited to be equal to monitor refresh rate
graphics cardmonitor
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This forum post explains VSync in as much detail as you could ever want.
http://hardforum.com/showthread.php?t=928593
The gist of it is that VSync stops screen tearing.
Screen tearing occurs because the frame buffer is half filled with the next frame when it is written to the screen. VSync introduces a back buffer inbetween the video card and the frame buffer which stores the next frame and then waits for the screen to refresh before copying itself to the frame buffer. The refresh signal is known as a VSync pulse (from analog). This stops the tearing from happening but can lead to a significant reduction in video performance in certain situations. These situations arise when framerate drops below refresh rate. In these situations your performance can drop by up to 50% in the worst case.
Triple Buffered VSync improves upon double buffered by adding another buffer and results in a much smaller performance penalty. In fact you will see frames as soon as the card can draw them (still timed with refreshes) because the card never has to sit idle, it always has a buffer it can write to. The only penalty is a small loss of VRAM to hold the buffers and the extra time taken to copy them out to the frame buffer. This is negligible.
Only worry about VSync if you are getting screen tearing. Don't worry about enabling it on a triple buffered system. If it is only double buffered then it's a personal choice, a tradeoff between refresh rate and tearing.
For the more interested:
Technically VSync does not require a second buffer. In situations where rendering the screen takes only a fraction of the time between refreshes VSync pulses can be used to time the writing of new information to the screenbuffer. If render time < refresh interval.
When you play a game the time taken to render is much greater. Writing the buffer on the VSync pulse would result in tearing whenever render time > refresh interval. The second buffer prevents this screen tearing from taking place but means that you can be looking at the same frame over several refreshes. It also means that once the back buffer is full there is no place for the card to write the next render until the VSync happens. This means that in practice VSync in a video game always introduces extra buffers.
Adding the third buffer gives the card a place to write the next render once the back buffer is full and awaiting the refresh.
This knowledge comes from programming display drivers for embedded systems.
It is hard to answer this question generically. Display "Mode Persistence", as it is called in the biz, is a notoriously fickle and config dependent feature. Key factors to consider:
- Display mode (Clone, or Extended Desktop)
- Graphics adapter (nVidia, ATI, etc)
- Version of Windows (generally pre-Win 7 or post-Win 7)
Display modes are handled differently for these different configs. I'd also suspect that the FPS hit for running in these different configs varies.
All that said, if you want an easy way to turn off your second (or third/fourth etc) displays, most modern graphics cards provide it. Look for a "hotkey" menu in the graphics adapter GUI. For example in Catalyst:
Here you can set keystrokes for various display mode switching. I believe you'd be looking for "Disable all non-Primary displays". There many other hotkey-able capabilities you may also find useful, if you are switching between gaming and "regular" computer use.
Best Answer
Tearing occurs when the graphics card's buffer is sent to the monitor while that same buffer is being changed. You still get tearing even if the FPS is limited to the refresh rate of the monitor because those things aren't locked together without vertical sync enabled.
Think of it like you're in a classroom, where the teacher is writing notes on the board. You're taking pictures of the board as the teacher is writing them. You want to take the picture when the board is full of notes. If you take a picture while the teacher is working, or while they're erasing part of the board to write new notes, your photo will be missing some of the notes.
It doesn't matter if during the class period you take 6 pictures and the teacher fills the board 6 times, right? You could take 6 pictures right at the beginning and miss everything. You could take the pictures evenly spaced (every 10 minutes, say) and miss stuff because the teacher takes longer or shorter to fill the board each time.
Instead, it matters that you take the picture at the right time. Your pictures must be "in sync" with the teacher.
"Taking the same number of pictures as there are blackboards full of notes" is locking the FPS to the refresh rate of the monitor. There's no guarantee that every time the monitor refreshes, the graphics card is between frames.
"Waiting until the blackboard is full of notes before taking a picture" is vertical sync. The graphics system is synchronized and thus only complete frames are shown.