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#include <simloop.h>
#include <assert.h>
static double min(double a, double b) { return a <= b ? a : b; }
static simloop_time_t ddt_from_fps(int fps) {
static constexpr double NANOSECONDS = 1e9;
return (fps == 0) ? 0 : (simloop_time_t)(NANOSECONDS / (double)fps);
}
Simloop simloop_make(const SimloopArgs* args) {
assert(args);
assert(args->update_fps > 0);
return (Simloop){
.frame = 0,
.update =
(SimloopTimeline){
.ddt = ddt_from_fps(args->update_fps),
.time = 0,
},
.render =
(SimloopTimeline){
.ddt = ddt_from_fps(args->max_render_fps),
.time = 0,
},
.percent_frame = 0.,
.first_iter = true,
};
}
static bool step_update(const Simloop* sim, SimloopTimeline* timeline) {
assert(sim);
assert(timeline);
assert(timeline->ddt > 0);
// If the update falls behind the clock, we advance by a single ddt increment
// per loop iteration here and give it a chance to catch up over subsequent
// iterations.
// This has the implication that percent_frame can fall out of range (>1) if
// we are not careful with how it is defined. See the general update function
// below.
const simloop_time_t dt = sim->clock - timeline->time;
const bool should_step = dt >= timeline->ddt;
timeline->time += should_step ? timeline->ddt : 0;
return should_step;
}
static bool step_render(const Simloop* sim, SimloopTimeline* timeline) {
assert(sim);
assert(timeline);
bool render = false;
if (timeline->ddt > 0) {
render = step_update(sim, timeline);
} else {
render = timeline->time < sim->clock;
timeline->time = sim->clock;
}
return render;
}
void simloop_update(Simloop* sim, simloop_time_t dt, SimloopOut* out) {
assert(sim);
assert(out);
sim->clock += dt;
// Simulation update.
const bool update_this_tick = step_update(sim, &sim->update);
// Simulation render.
const bool render_this_tick =
step_render(sim, &sim->render) ||
sim->first_iter; // Trigger an initial render on the first frame.
// Interpolator for smooth animation.
// If rendering is not frame-rate capped, then its timeline should always be
// at least as recent as the update's. Otherwise, it is possible for the
// rendering timeline to be behind.
// If the update falls behind the clock, then percent_frame can fall out of
// range (>1) if we are not careful. We impose that it is strictly never >1
// to account for this case.
assert(sim->update.ddt > 0);
assert(
(sim->render.ddt == 0) ? (sim->update.time <= sim->render.time) : true);
sim->percent_frame =
(sim->render.time >= sim->update.time)
? min(1., ((double)(sim->render.time - sim->update.time) /
(double)sim->update.ddt))
: sim->percent_frame;
assert((0. <= sim->percent_frame) && (sim->percent_frame <= 1.));
// Loop state update.
sim->frame += (update_this_tick ? 1 : 0);
sim->first_iter = false;
out->frame = sim->frame;
out->render_elapsed = sim->render.time;
out->update_elapsed = sim->update.time;
out->update_dt = sim->update.ddt;
out->percent_frame = sim->percent_frame;
out->should_update = update_this_tick;
out->should_render = render_this_tick;
}
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