Improved consistency and accuracy of frame update timing
Previously the engine's main loop started by waiting until enough time had passed for the requested FPS (refresh-rate-maximum), after which it proceeded to process events, draw the frame, and finally do the buffer swap. Because it is impossible to predict how long tickers and drawing will take, this meant that it was difficult to accurately retain the configured FPS.
This commit changes the timer so that the wait is done right before the GL buffer swap. Consequently there is a much better chance of the frame becoming visible exactly at the correct time according to the configured FPS.
Also, the wait for GL buffer swap is no longer dependent on the value of "settics"; the configured tics-per-second value only affects tickers and other event processing. Frame update timing is now always done using the real, most accurate clock time available to Doomsday. This fixes the refresh problem where a very low value for settics would start making everything choppier.
Previously, if RunTics noticed that enough time had not passed since the previous frame, it would attempt to sleep 3 ms and check again. This would result in the realized frame time being too long (up to 3 ms), as the loop would only end until the optimal time had already passed. Consequently the realized FPS was always significantly lower than "refresh-rate-maximum". Now the frame update attempts to sleep exactly as long as necessary in order to start the new frame at the correct time.
Added cvar "rend-info-deltas-frametime" for printing information about the difference between realized frame time deltas and the optimal deltas. Note that the printed "min" delta should stay zero; whenever it's larger than zero it means that GL updates are constantly missing their optimal configured delta time and that the configured target FPS can be lowered.
Note: Time deltas are measured in integer milliseconds as we don't have the capability to measure time with microsecond accuracy.
Todo for later: Adjust max FPS automatically to keep the min delta at zero?
Added by skyjake about 13 years ago
Added by
Improved consistency and accuracy of frame update timing
Previously the engine's main loop started by waiting until enough time had
passed for the requested FPS (refresh-rate-maximum), after which it proceeded
to process events, draw the frame, and finally do the buffer swap. Because it
is impossible to predict how long tickers and drawing will take, this meant
that it was difficult to accurately retain the configured FPS.
This commit changes the timer so that the wait is done right before the GL
buffer swap. Consequently there is a much better chance of the frame becoming
visible exactly at the correct time according to the configured FPS.
Also, the wait for GL buffer swap is no longer dependent on the value of
"settics"; the configured tics-per-second value only affects tickers and other
event processing. Frame update timing is now always done using the real, most
accurate clock time available to Doomsday. This fixes the refresh problem
where a very low value for settics would start making everything choppier.
Previously, if RunTics noticed that enough time had not passed since the
previous frame, it would attempt to sleep 3 ms and check again. This would
result in the realized frame time being too long (up to 3 ms), as the loop
would only end until the optimal time had already passed. Consequently the
realized FPS was always significantly lower than "refresh-rate-maximum". Now
the frame update attempts to sleep exactly as long as necessary in order to
start the new frame at the correct time.
Added cvar "rend-info-deltas-frametime" for printing information about the
difference between realized frame time deltas and the optimal deltas. Note
that the printed "min" delta should stay zero; whenever it's larger than zero
it means that GL updates are constantly missing their optimal configured delta
time and that the configured target FPS can be lowered.
Note: Time deltas are measured in integer milliseconds as we don't have the
capability to measure time with microsecond accuracy.
Todo for later: Adjust max FPS automatically to keep the min delta at zero?