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[WIP] Add semi-fixed timestep and physics time stretching for global timescale #30798

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[WIP] Add semi-fixed timestep and physics time stretching for global timescale #30798

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5 changes: 5 additions & 0 deletions core/engine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,10 @@ float Engine::get_time_scale() const {
return _time_scale;
}

bool Engine::get_physics_stretch_ticks() const {
return _physics_stretch_ticks;
}

Dictionary Engine::get_version_info() const {

Dictionary dict;
Expand Down Expand Up @@ -232,6 +236,7 @@ Engine::Engine() {
_fps = 1;
_target_fps = 0;
_time_scale = 1.0;
_physics_stretch_ticks = true;
_pixel_snap = false;
_physics_frames = 0;
_idle_frames = 0;
Expand Down
2 changes: 2 additions & 0 deletions core/engine.h
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,7 @@ class Engine {
float _fps;
int _target_fps;
float _time_scale;
bool _physics_stretch_ticks;
bool _pixel_snap;
uint64_t _physics_frames;
float _physics_interpolation_fraction;
Expand Down Expand Up @@ -100,6 +101,7 @@ class Engine {

void set_time_scale(float p_scale);
float get_time_scale() const;
bool get_physics_stretch_ticks() const;

void set_frame_delay(uint32_t p_msec);
uint32_t get_frame_delay() const;
Expand Down
95 changes: 61 additions & 34 deletions main/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,8 @@
#include "editor/project_manager.h"
#endif

#include <stdint.h>

/* Static members */

// Singletons
Expand Down Expand Up @@ -1026,6 +1028,10 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
Engine::get_singleton()->set_iterations_per_second(GLOBAL_DEF("physics/common/physics_fps", 60));
ProjectSettings::get_singleton()->set_custom_property_info("physics/common/physics_fps", PropertyInfo(Variant::INT, "physics/common/physics_fps", PROPERTY_HINT_RANGE, "1,120,1,or_greater"));
Engine::get_singleton()->set_physics_jitter_fix(GLOBAL_DEF("physics/common/physics_jitter_fix", 0.5));
GLOBAL_DEF("physics/common/timestep/method", "Jitter Fix");
ProjectSettings::get_singleton()->set_custom_property_info("physics/common/timestep/method", PropertyInfo(Variant::STRING, "physics/common/timestep/method", PROPERTY_HINT_ENUM, "Jitter Fix,Fixed,Semi Fixed"));
Engine::get_singleton()->_physics_stretch_ticks = GLOBAL_DEF("physics/common/timestep/timescale_stretch_ticks", true);

Engine::get_singleton()->set_target_fps(GLOBAL_DEF("debug/settings/fps/force_fps", 0));
ProjectSettings::get_singleton()->set_custom_property_info("debug/settings/fps/force_fps", PropertyInfo(Variant::INT, "debug/settings/fps/force_fps", PROPERTY_HINT_RANGE, "0,120,1,or_greater"));

Expand Down Expand Up @@ -1856,6 +1862,35 @@ bool Main::is_iterating() {
static uint64_t physics_process_max = 0;
static uint64_t idle_process_max = 0;

// returns usecs taken by the physics tick
uint64_t Main::physics_tick(float p_physics_delta) {
uint64_t physics_begin = OS::get_singleton()->get_ticks_usec();

PhysicsServer::get_singleton()->sync();
PhysicsServer::get_singleton()->flush_queries();

Physics2DServer::get_singleton()->sync();
Physics2DServer::get_singleton()->flush_queries();

if (OS::get_singleton()->get_main_loop()->iteration(p_physics_delta)) {
// UINT64_MAX indicates we want to stop the loop through the physics iterations
return UINT64_MAX;
}

message_queue->flush();

PhysicsServer::get_singleton()->step(p_physics_delta);

Physics2DServer::get_singleton()->end_sync();
Physics2DServer::get_singleton()->step(p_physics_delta);

message_queue->flush();

Engine::get_singleton()->_physics_frames++;

return OS::get_singleton()->get_ticks_usec() - physics_begin;
}

bool Main::iteration() {

//for now do not error on this
Expand All @@ -1865,21 +1900,21 @@ bool Main::iteration() {

uint64_t ticks = OS::get_singleton()->get_ticks_usec();
Engine::get_singleton()->_frame_ticks = ticks;
main_timer_sync.set_cpu_ticks_usec(ticks);
main_timer_sync.set_fixed_fps(fixed_fps);

uint64_t ticks_elapsed = ticks - last_ticks;

int physics_fps = Engine::get_singleton()->get_iterations_per_second();
float frame_slice = 1.0 / physics_fps;

float time_scale = Engine::get_singleton()->get_time_scale();
// main_timer_sync will deal with time_scale and limiting the max number of physics ticks
MainFrameTime advance;
main_timer_sync.advance(advance, physics_fps, ticks, fixed_fps);

MainFrameTime advance = main_timer_sync.advance(frame_slice, physics_fps);
double step = advance.idle_step;
double scaled_step = step * time_scale;
double scaled_step = advance.scaled_frame_delta;

Engine::get_singleton()->_frame_step = step;
// Note Engine::_frame_step was previously the step unadjusted for timescale.
// It was unused within Godot, although perhaps used in custom Modules, I'm assuming this was a bug
// as scaled step makes more sense.
Engine::get_singleton()->_frame_step = scaled_step;
Engine::get_singleton()->_physics_interpolation_fraction = advance.interpolation_fraction;

uint64_t physics_process_ticks = 0;
Expand All @@ -1889,50 +1924,40 @@ bool Main::iteration() {

last_ticks = ticks;

static const int max_physics_steps = 8;
if (fixed_fps == -1 && advance.physics_steps > max_physics_steps) {
step -= (advance.physics_steps - max_physics_steps) * frame_slice;
advance.physics_steps = max_physics_steps;
}

bool exit = false;

Engine::get_singleton()->_in_physics = true;

for (int iters = 0; iters < advance.physics_steps; ++iters) {
float physics_delta = advance.physics_fixed_step_delta;

uint64_t physics_begin = OS::get_singleton()->get_ticks_usec();
for (int iters = 0; iters < advance.physics_steps; ++iters) {

PhysicsServer::get_singleton()->sync();
PhysicsServer::get_singleton()->flush_queries();
// special case, if using variable physics timestep and the last physics step
if (advance.physics_variable_step && (iters == (advance.physics_steps - 1))) {
// substitute the variable delta
physics_delta = advance.physics_variable_step_delta;
}

Physics2DServer::get_singleton()->sync();
Physics2DServer::get_singleton()->flush_queries();
// returns the time taken by the physics tick
uint64_t physics_usecs = physics_tick(physics_delta);

if (OS::get_singleton()->get_main_loop()->iteration(frame_slice * time_scale)) {
// in the special case of wanting to exit the loop we are passing
// UINT64_MAX which will never occur normally.
if (physics_usecs == UINT64_MAX) {
exit = true;
break;
}

message_queue->flush();

PhysicsServer::get_singleton()->step(frame_slice * time_scale);

Physics2DServer::get_singleton()->end_sync();
Physics2DServer::get_singleton()->step(frame_slice * time_scale);

message_queue->flush();

physics_process_ticks = MAX(physics_process_ticks, OS::get_singleton()->get_ticks_usec() - physics_begin); // keep the largest one for reference
physics_process_max = MAX(OS::get_singleton()->get_ticks_usec() - physics_begin, physics_process_max);
Engine::get_singleton()->_physics_frames++;
// performance stats
physics_process_ticks = MAX(physics_process_ticks, physics_usecs); // keep the largest one for reference
physics_process_max = MAX(physics_usecs, physics_process_max);
}

Engine::get_singleton()->_in_physics = false;

uint64_t idle_begin = OS::get_singleton()->get_ticks_usec();

if (OS::get_singleton()->get_main_loop()->idle(step * time_scale)) {
if (OS::get_singleton()->get_main_loop()->idle(scaled_step)) {
exit = true;
}
message_queue->flush();
Expand Down Expand Up @@ -1965,6 +1990,8 @@ bool Main::iteration() {

if (script_debugger) {
if (script_debugger->is_profiling()) {
// note that frame_slice is original physics delta, before time_scale applied
float frame_slice = 1.0 / physics_fps;
script_debugger->profiling_set_frame_times(USEC_TO_SEC(frame_time), USEC_TO_SEC(idle_process_ticks), USEC_TO_SEC(physics_process_ticks), frame_slice);
}
script_debugger->idle_poll();
Expand Down
1 change: 1 addition & 0 deletions main/main.h
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@ class Main {
static bool start();

static bool iteration();
static uint64_t physics_tick(float p_physics_delta);
static void force_redraw();

static bool is_iterating();
Expand Down
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