03-27-2011, 05:42 AM
(This post was last modified: 03-27-2011, 06:45 AM by nosisab Ken Keleh.)
Let's try to remove the misunderstandings about the refresh rate and FPS once and for all.
The refresh rate is fixed for the system, does not matter if it is a console, TV or computer. In TV it's fixed by the adopted standard, the only ones that matters here is (European) PAL N =50 frames per second and NTSC=60 frames per second (yes, I said frames but nothing about what is draw in the canvases), each refresh pass is a canvas where things will be draw.
Computer is more flexible because it is not tied with any TV standard and the video driver need only to provide the same refresh rate the monitor is capable. At old CRT that is an important factor and the higher the best because the flickering. Modern monitors still benefits from higher refresh rate but not at the same extent and 60 is a common value, 120 is reserved for very high accuracy and 3D view experience.
So, does not matter the system being used, it will always keep the refresh rate steady under risk the image being totally distorted/lost. Many people here may still recall what happens when the vertical or horizontal synch was lost in old TV devices, with the vertical desynch the image (entire canvas) begins to slide down or up slowly, while in the horizontal desynch the image becomes a series of diagonal strips.
Now that we "got" steady canvases repeating exactly the expected number of times we can draw over it as many times as we wish. And it's perfectly possible to draw only once and that draw pushed in a buffer the video driver would output that buffer to the monitor at any rate and the final result would be a perfect still image, does not matter if it's draw at 1 FPS or 200 FPS.
OK, we are interested in movement, not on still pictures, so things are constantly changing from one frame to the next. Experience showed 24 FPS is enough to the human eye see the changes as smooth provided things are not changing too fast. If we look at a video frame by frame we can see how the moving elements changes position, slow moving things get smaller shifts than the fastest ones.
That mean than below 20 FPS the eye is perfectly able to detect the lack of smoothness even for low moving things and then it should be avoided at all cost or it will seen more a slide show than a movie.
Still it's not yet clear how the movement in each frame is directed. In almost all computer applications the changes in moving elements are synchronized by real time. Let's say the body X is to move from the point A to point B in 6 seconds it will do it in 6 seconds does not matter if the FPS is 30 or 300 (the only perceptible difference would be verifying the shift it gets at each frame). This is what explain why PC games seem tolerant with FPS changes.
Now let us look to movements that are synchronized with the frame. The most obvious example is an actual movie where the whole image is already impressed on the canvas... any change in the FPS is translated into slowdown or fast pace. In a movie the FPS and the refresh rate are the same thing, so we see the distinction is only about how fast the actual canvas is draw. Difference between the FPS and vertical refresh can lead to images sectors shifts and so may be desirable to keep the FPS and vertical refresh so they begin the scan at same time what can lead to FPS capped as low as half or even less than the monitor refresh rate, not that big deal in PC games but a killer in console (and console emulators), thus disabling the video driver Vsynch can help alot.
All this got us to the console games finally. Most are designed so it's timings are synchronized with the FPS, very alike the TV itself. the above body X moving from point A to point B is not dependent on time anymore, it has a fixed shift at each frame. If in the PC it would perform the whole trip in 6 seconds mattering not the FPS, in console games it would move at half speed under half FPS as it was a movie and not dynamically draw.
Not only the image may be synched this way, other parameters might be equally dependent on the FPS. The other more perceptible being the sound itself. It's easy to perceive that in this harsh scenery, raw low FPS is BAD, not much better is high FPS.
To try and help the machines which cannot keep the FPS at expected value the reason for the hacks, one very significant is the VU cycle stealing. It's function is to help GS to achieve the correct FPS, the price being: to do so, it reduces the amount of actual output, lets say it allows GS to draw the canvas more frequently but actual changes between the drawings are reduced, what can lead to lag and slow motion in sensible games. Still it should not be completely discarded because albeit not ideal that lag may be better than the raw low FPS that can break other things like the sound, for example (a few games get sound desynch too but it's another history). EE Cyclerate is a more probable suspect for sound issues.
I hope this long post brings light about the differences between the FPS and Refresh rate. Mainly in the understanding this last represent the canvases and the former represents the actual drawings over these canvases. The video driver is smart enough to repeat whatever is in the buffer to keep the canvas filled with the actual image, even if no new drawing is done on it. Sadly I don't have SotC so I can't tell how it looks and feels and how it behaves under different speed hacks or none at all.
The bottom line is PCSX2 must struggle not only to emulate the base PS2 refresh rate as it need to provide enough FPS to fill it, I think it is what Koji meant.
The refresh rate is fixed for the system, does not matter if it is a console, TV or computer. In TV it's fixed by the adopted standard, the only ones that matters here is (European) PAL N =50 frames per second and NTSC=60 frames per second (yes, I said frames but nothing about what is draw in the canvases), each refresh pass is a canvas where things will be draw.
Computer is more flexible because it is not tied with any TV standard and the video driver need only to provide the same refresh rate the monitor is capable. At old CRT that is an important factor and the higher the best because the flickering. Modern monitors still benefits from higher refresh rate but not at the same extent and 60 is a common value, 120 is reserved for very high accuracy and 3D view experience.
So, does not matter the system being used, it will always keep the refresh rate steady under risk the image being totally distorted/lost. Many people here may still recall what happens when the vertical or horizontal synch was lost in old TV devices, with the vertical desynch the image (entire canvas) begins to slide down or up slowly, while in the horizontal desynch the image becomes a series of diagonal strips.
Now that we "got" steady canvases repeating exactly the expected number of times we can draw over it as many times as we wish. And it's perfectly possible to draw only once and that draw pushed in a buffer the video driver would output that buffer to the monitor at any rate and the final result would be a perfect still image, does not matter if it's draw at 1 FPS or 200 FPS.
OK, we are interested in movement, not on still pictures, so things are constantly changing from one frame to the next. Experience showed 24 FPS is enough to the human eye see the changes as smooth provided things are not changing too fast. If we look at a video frame by frame we can see how the moving elements changes position, slow moving things get smaller shifts than the fastest ones.
That mean than below 20 FPS the eye is perfectly able to detect the lack of smoothness even for low moving things and then it should be avoided at all cost or it will seen more a slide show than a movie.
Still it's not yet clear how the movement in each frame is directed. In almost all computer applications the changes in moving elements are synchronized by real time. Let's say the body X is to move from the point A to point B in 6 seconds it will do it in 6 seconds does not matter if the FPS is 30 or 300 (the only perceptible difference would be verifying the shift it gets at each frame). This is what explain why PC games seem tolerant with FPS changes.
Now let us look to movements that are synchronized with the frame. The most obvious example is an actual movie where the whole image is already impressed on the canvas... any change in the FPS is translated into slowdown or fast pace. In a movie the FPS and the refresh rate are the same thing, so we see the distinction is only about how fast the actual canvas is draw. Difference between the FPS and vertical refresh can lead to images sectors shifts and so may be desirable to keep the FPS and vertical refresh so they begin the scan at same time what can lead to FPS capped as low as half or even less than the monitor refresh rate, not that big deal in PC games but a killer in console (and console emulators), thus disabling the video driver Vsynch can help alot.
All this got us to the console games finally. Most are designed so it's timings are synchronized with the FPS, very alike the TV itself. the above body X moving from point A to point B is not dependent on time anymore, it has a fixed shift at each frame. If in the PC it would perform the whole trip in 6 seconds mattering not the FPS, in console games it would move at half speed under half FPS as it was a movie and not dynamically draw.
Not only the image may be synched this way, other parameters might be equally dependent on the FPS. The other more perceptible being the sound itself. It's easy to perceive that in this harsh scenery, raw low FPS is BAD, not much better is high FPS.
To try and help the machines which cannot keep the FPS at expected value the reason for the hacks, one very significant is the VU cycle stealing. It's function is to help GS to achieve the correct FPS, the price being: to do so, it reduces the amount of actual output, lets say it allows GS to draw the canvas more frequently but actual changes between the drawings are reduced, what can lead to lag and slow motion in sensible games. Still it should not be completely discarded because albeit not ideal that lag may be better than the raw low FPS that can break other things like the sound, for example (a few games get sound desynch too but it's another history). EE Cyclerate is a more probable suspect for sound issues.
I hope this long post brings light about the differences between the FPS and Refresh rate. Mainly in the understanding this last represent the canvases and the former represents the actual drawings over these canvases. The video driver is smart enough to repeat whatever is in the buffer to keep the canvas filled with the actual image, even if no new drawing is done on it. Sadly I don't have SotC so I can't tell how it looks and feels and how it behaves under different speed hacks or none at all.
The bottom line is PCSX2 must struggle not only to emulate the base PS2 refresh rate as it need to provide enough FPS to fill it, I think it is what Koji meant.
Imagination is where we are truly real
so let's highlight the final bit since it hopefully is enough by itself.