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Fix negative delta arguments backport to 3.x #52947

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Sep 29, 2021
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Fix negative delta arguments backport to 3.x #52947

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43 changes: 42 additions & 1 deletion main/main_timer_sync.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
}
Expand Down Expand Up @@ -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());
Expand All @@ -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
Expand Down Expand Up @@ -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;

Expand All @@ -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;

Expand Down