From 6be702bace06604281b3358ce7015086bcb7e2fb Mon Sep 17 00:00:00 2001 From: Manuel Moos Date: Sat, 15 Feb 2020 23:50:25 +0100 Subject: [PATCH] Fix negative delta arguments 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 --- main/main_timer_sync.cpp | 43 +++++++++++++++++++++++++++++++++++++++- 1 file changed, 42 insertions(+), 1 deletion(-) diff --git a/main/main_timer_sync.cpp b/main/main_timer_sync.cpp index 0d172be65e..42023e5a2f 100644 --- a/main/main_timer_sync.cpp +++ b/main/main_timer_sync.cpp @@ -57,7 +57,7 @@ int MainTimerSync::get_average_physics_steps(double &p_min, double &p_max) { const double typical_lower = typical_physics_steps[i]; const double 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; } @@ -105,6 +105,12 @@ MainFrameTime MainTimerSync::advance_core(double p_physics_step, int p_physics_t } } +#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_physics_ticks_per_second + get_physics_jitter_fix()); @@ -124,6 +130,10 @@ MainFrameTime MainTimerSync::advance_core(double p_physics_step, int p_physics_t } } + if (ret.physics_steps < 0) { + ret.physics_steps = 0; + } + time_accum -= ret.physics_steps * p_physics_step; // keep track of accumulated step counts @@ -151,6 +161,9 @@ MainFrameTime MainTimerSync::advance_checked(double p_physics_step, int p_physic p_process_step = 1.0 / fixed_fps; } + float min_output_step = p_process_step / 8; + min_output_step = MAX(min_output_step, 1E-6); + // compensate for last deficit p_process_step += time_deficit; @@ -177,9 +190,37 @@ MainFrameTime MainTimerSync::advance_checked(double p_physics_step, int p_physic // last clamping: make sure time_accum is between 0 and p_physics_step for consistency between physics and process ret.clamp_process_step(process_minus_accum, process_minus_accum + p_physics_step); + // all the operations above may have turned ret.p_process_step negative or zero, keep a minimal value + if (ret.process_step < min_output_step) { + ret.process_step = min_output_step; + } + // restore time_accum time_accum = ret.process_step - process_minus_accum; + // forcing ret.process_step to be positive may trigger a violation of the + // promise that time_accum is between 0 and p_physics_step +#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_physics_step) { + const int extra_physics_steps = floor(time_accum * p_physics_ticks_per_second); + time_accum -= extra_physics_steps * p_physics_step; + 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_physics_step + 1E-7) { + WARN_PRINT_ONCE("Final value of `time_accum` is larger than `p_physics_step`. It should always be between 0 and `p_physics_step`. This hints at an engine bug."); + } +#endif + // track deficit time_deficit = p_process_step - ret.process_step;