Nou hieronder vind je de post van degene die het uitgezocht heeft
WARNING: EXTREMELY long post with only 1 smiley -- but it's worth it, as I answer pretty much every physics / FPS question in quake 3.
Earlier this evening, Ctrl told me that he was dissatisfied with my previous explanation of why your fps affects jumping. So, I did some more research. Specifically, I wrote a mod to measure your jumping.
Here are the key points that I discovered:
(1) The final velocity vectors are clamped to integers every time the player movement code is called. This gets called once per frame for fast clients, but never less than 20 times per second.
(2) This conversion is done by the equation (int)x, where "x" is a floating point value.
(3) The integer conversion done by the Q3 vm *IS NOT ANSI COMPLIENT*. ANSI C specifies that integer conversion is done by ignoring the fraction. The Q3 vm does it by rounding to the nearest integer.
This third point explains exactly why DLL's have slower speeds and jump heights than QVM's. In a QVM, the rounding is to nearest integer, so errors will tend to cancel out. In a DLL, rounding is always towards 0, so errors always reduce your speed and will always accumulate. The rounding error in a DLL always acts as extra friction. I expect you can get around this problem in DLL's by rewriting the "SnapVector" macro to emulate the QVM's rounding method.
Now, back to the jumps. In theory, the rounding errors should cancel out over the number of frames in a typical jump. This assumes that the fraction can be any value with equal probability. However, in practice, this is not the case. Each frame tends to be the same time as the previous one. The change in velocity is the acceleration times the frame time. Acceleration is due to gravity, and is therefore constant. Frame time is also nearly constant, so the change in velocity is also nearly constant in each frame. Since velocity always starts as an integer, and the change is always nearly the same, under a constant fps rounding has nearly the same error each frame. With a constant frame rate, Q3's rounding errors will tend to accumulate. For some frame rates, this will always round down; for others, it will always round up.
Based on this, the ideal frame rate for jumping distance is the highest one your computer can maintain that gets a fraction remainder near 0.5, but always greater than 0.5. Q3's gravity is 800, so you want the fractional part of 800/fps to be greater than 0.5. To protect against frame rate fluctuations, you'd also want nearby frame rates to have fractions greater than 0.5. Lastly, you want there to be as many frames as possible, so that the most possible positive error gets accumulated.
When you jump, you are given 270 units / second of upward velocity, with a gravity of 800 units / second squared. Basic physics tells us that you should reach a maximum height of 45.5625 units after 0.3375 seconds. The height value shows the actual height of your jump. Frames is the number of frames the server used in reaching that height. Extra Vel is the approximate additional velocity you gained from rounding errors. Extra Hgt is the approximate additional height you gained from rounding errors.
Complete uitleg vind je op
www.quake3world.com/ubb/Forum3/HTML/015173.html
en
www.quake3world.com/ubb/Forum3/HTML/010927.html
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