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Fix negative delta arguments

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Three attack points, all after the regular calculations:
1. Prevent negative physics timestep counts. They could occur if
   physics_jtter_fix is changed at runtime.
2. idle_step is not allowed to go below 1/8th of the input step.
   That could happen on physics_jitter_fix changes or heavily
   fluctuating performance.
3. Prevent that the idle_step modification breaks the promise
   that Engine.get_physics_interpolation_fraction() is between
   0 and 1 by doing more physics steps than the base system wants.

Fixes #26887

Co-authored-by: Hugo Locurcio <hugo.locurcio@hugo.pro>
Cherry-Pick from 6be702bace.
This commit is contained in:
Manuel Moos 2020-02-15 23:50:25 +01:00
parent 23bb5883cb
commit f8e62424c5
1 changed files with 42 additions and 1 deletions
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43
main/main_timer_sync.cpp
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@ -304,7 +304,7 @@ int MainTimerSync::get_average_physics_steps(float &p_min, float &p_max) {
const float typical_lower = typical_physics_steps[i];
const float current_min = typical_lower / (i + 1);
if (current_min > p_max) {
return i; // bail out of further restrictions would void the interval
return i; // bail out if further restrictions would void the interval
} else if (current_min > p_min) {
p_min = current_min;
}
@ -352,6 +352,12 @@ MainFrameTime MainTimerSync::advance_core(float p_frame_slice, int p_iterations_
}
}
#ifdef DEBUG_ENABLED
if (max_typical_steps < 0) {
WARN_PRINT_ONCE("`max_typical_steps` is negative. This could hint at an engine bug or system timer misconfiguration.");
}
#endif
// try to keep it consistent with previous iterations
if (ret.physics_steps < min_typical_steps) {
const int max_possible_steps = floor((time_accum)*p_iterations_per_second + get_physics_jitter_fix());
@ -371,6 +377,10 @@ MainFrameTime MainTimerSync::advance_core(float p_frame_slice, int p_iterations_
}
}
if (ret.physics_steps < 0) {
ret.physics_steps = 0;
}
time_accum -= ret.physics_steps * p_frame_slice;
// keep track of accumulated step counts
@ -398,6 +408,9 @@ MainFrameTime MainTimerSync::advance_checked(float p_frame_slice, int p_iteratio
p_idle_step = 1.0 / fixed_fps;
}
float min_output_step = p_idle_step / 8;
min_output_step = MAX(min_output_step, 1E-6);
// compensate for last deficit
p_idle_step += time_deficit;
@ -424,9 +437,37 @@ MainFrameTime MainTimerSync::advance_checked(float p_frame_slice, int p_iteratio
// last clamping: make sure time_accum is between 0 and p_frame_slice for consistency between physics and idle
ret.clamp_idle(idle_minus_accum, idle_minus_accum + p_frame_slice);
// all the operations above may have turned ret.idle_step negative or zero, keep a minimal value
if (ret.idle_step < min_output_step) {
ret.idle_step = min_output_step;
}
// restore time_accum
time_accum = ret.idle_step - idle_minus_accum;
// forcing ret.idle_step to be positive may trigger a violation of the
// promise that time_accum is between 0 and p_frame_slice
#ifdef DEBUG_ENABLED
if (time_accum < -1E-7) {
WARN_PRINT_ONCE("Intermediate value of `time_accum` is negative. This could hint at an engine bug or system timer misconfiguration.");
}
#endif
if (time_accum > p_frame_slice) {
const int extra_physics_steps = floor(time_accum * p_iterations_per_second);
time_accum -= extra_physics_steps * p_frame_slice;
ret.physics_steps += extra_physics_steps;
}
#ifdef DEBUG_ENABLED
if (time_accum < -1E-7) {
WARN_PRINT_ONCE("Final value of `time_accum` is negative. It should always be between 0 and `p_physics_step`. This hints at an engine bug.");
}
if (time_accum > p_frame_slice + 1E-7) {
WARN_PRINT_ONCE("Final value of `time_accum` is larger than `p_frame_slice`. It should always be between 0 and `p_frame_slice`. This hints at an engine bug.");
}
#endif
// track deficit
time_deficit = p_idle_step - ret.idle_step;