Core: Re-write frame limiter

Now based on std::chrono, and also works in terms of emulated time
instead of frames, so we can in the future frame-limit even when the
display is disabled, etc.

The frame limiter can also be enabled along with v-sync now, which
should be useful for those with displays running at more than 60 Hz.

src/core/core.h

@@ -94,6 +94,7 @@ public:
     }
 
     PerfStats perf_stats;
+    FrameLimiter frame_limiter;
 
 private:
     /**

src/core/hw/gpu.cpp

@@ -8,17 +8,13 @@
 #include "common/color.h"
 #include "common/common_types.h"
 #include "common/logging/log.h"
-#include "common/math_util.h"
 #include "common/microprofile.h"
-#include "common/thread.h"
-#include "common/timer.h"
 #include "common/vector_math.h"
 #include "core/core_timing.h"
 #include "core/hle/service/gsp_gpu.h"
 #include "core/hw/gpu.h"
 #include "core/hw/hw.h"
 #include "core/memory.h"
-#include "core/settings.h"
 #include "core/tracer/recorder.h"
 #include "video_core/command_processor.h"
 #include "video_core/debug_utils/debug_utils.h"
@@ -35,16 +31,6 @@ Regs g_regs;
 const u64 frame_ticks = BASE_CLOCK_RATE_ARM11 / SCREEN_REFRESH_RATE;
 /// Event id for CoreTiming
 static int vblank_event;
-/// Total number of frames drawn
-static u64 frame_count;
-/// Start clock for frame limiter
-static u32 time_point;
-/// Total delay caused by slow frames
-static float time_delay;
-constexpr float FIXED_FRAME_TIME = 1000.0f / SCREEN_REFRESH_RATE;
-// Max lag caused by slow frames. Can be adjusted to compensate for too many slow frames. Higher
-// values increases time needed to limit frame rate after spikes
-constexpr float MAX_LAG_TIME = 18;
 
 template <typename T>
 inline void Read(T& var, const u32 raw_addr) {
@@ -522,24 +508,8 @@ template void Write<u32>(u32 addr, const u32 data);
 template void Write<u16>(u32 addr, const u16 data);
 template void Write<u8>(u32 addr, const u8 data);
 
-static void FrameLimiter() {
-    time_delay += FIXED_FRAME_TIME;
-    time_delay = MathUtil::Clamp(time_delay, -MAX_LAG_TIME, MAX_LAG_TIME);
-    s32 desired_time = static_cast<s32>(time_delay);
-    s32 elapsed_time = static_cast<s32>(Common::Timer::GetTimeMs() - time_point);
-
-    if (elapsed_time < desired_time) {
-        Common::SleepCurrentThread(desired_time - elapsed_time);
-    }
-
-    u32 frame_time = Common::Timer::GetTimeMs() - time_point;
-
-    time_delay -= frame_time;
-}
-
 /// Update hardware
 static void VBlankCallback(u64 userdata, int cycles_late) {
-    frame_count++;
     VideoCore::g_renderer->SwapBuffers();
 
     // Signal to GSP that GPU interrupt has occurred
@@ -550,12 +520,6 @@ static void VBlankCallback(u64 userdata, int cycles_late) {
     Service::GSP::SignalInterrupt(Service::GSP::InterruptId::PDC0);
     Service::GSP::SignalInterrupt(Service::GSP::InterruptId::PDC1);
 
-    if (!Settings::values.use_vsync && Settings::values.toggle_framelimit) {
-        FrameLimiter();
-    }
-
-    time_point = Common::Timer::GetTimeMs();
-
     // Reschedule recurrent event
     CoreTiming::ScheduleEvent(frame_ticks - cycles_late, vblank_event);
 }
@@ -590,9 +554,6 @@ void Init() {
     framebuffer_sub.color_format.Assign(Regs::PixelFormat::RGB8);
     framebuffer_sub.active_fb = 0;
 
-    frame_count = 0;
-    time_point = Common::Timer::GetTimeMs();
-
     vblank_event = CoreTiming::RegisterEvent("GPU::VBlankCallback", VBlankCallback);
     CoreTiming::ScheduleEvent(frame_ticks, vblank_event);
 

src/core/perf_stats.cpp

@@ -4,11 +4,16 @@
 
 #include <chrono>
 #include <mutex>
+#include <thread>
+#include "common/math_util.h"
 #include "core/hw/gpu.h"
 #include "core/perf_stats.h"
+#include "core/settings.h"
 
+using namespace std::chrono_literals;
 using DoubleSecs = std::chrono::duration<double, std::chrono::seconds::period>;
 using std::chrono::duration_cast;
+using std::chrono::microseconds;
 
 namespace Core {
 
@@ -69,4 +74,32 @@ double PerfStats::GetLastFrameTimeScale() {
     return duration_cast<DoubleSecs>(previous_frame_length).count() / FRAME_LENGTH;
 }
 
+void FrameLimiter::DoFrameLimiting(u64 current_system_time_us) {
+    // Max lag caused by slow frames. Can be adjusted to compensate for too many slow frames. Higher
+    // values increases time needed to limit frame rate after spikes.
+    constexpr microseconds MAX_LAG_TIME_US = 25ms;
+
+    if (!Settings::values.toggle_framelimit) {
+        return;
+    }
+
+    auto now = Clock::now();
+
+    frame_limiting_delta_err += microseconds(current_system_time_us - previous_system_time_us);
+    frame_limiting_delta_err -= duration_cast<microseconds>(now - previous_walltime);
+    frame_limiting_delta_err =
+        MathUtil::Clamp(frame_limiting_delta_err, -MAX_LAG_TIME_US, MAX_LAG_TIME_US);
+
+    if (frame_limiting_delta_err > microseconds::zero()) {
+        std::this_thread::sleep_for(frame_limiting_delta_err);
+
+        auto now_after_sleep = Clock::now();
+        frame_limiting_delta_err -= duration_cast<microseconds>(now_after_sleep - now);
+        now = now_after_sleep;
+    }
+
+    previous_system_time_us = current_system_time_us;
+    previous_walltime = now;
+}
+
 } // namespace Core

src/core/perf_stats.h

@@ -55,4 +55,20 @@ private:
     u32 game_frames = 0;
 };
 
+class FrameLimiter {
+public:
+    using Clock = std::chrono::high_resolution_clock;
+
+    void DoFrameLimiting(u64 current_system_time_us);
+
+private:
+    /// Emulated system time (in microseconds) at the last limiter invocation
+    u64 previous_system_time_us = 0;
+    /// Walltime at the last limiter invocation
+    Clock::time_point previous_walltime = Clock::now();
+
+    /// Accumulated difference between walltime and emulated time
+    std::chrono::microseconds frame_limiting_delta_err{0};
+};
+
 } // namespace Core

src/video_core/renderer_opengl/renderer_opengl.cpp

@@ -10,8 +10,8 @@
 #include "common/assert.h"
 #include "common/bit_field.h"
 #include "common/logging/log.h"
-#include "common/synchronized_wrapper.h"
 #include "core/core.h"
+#include "core/core_timing.h"
 #include "core/frontend/emu_window.h"
 #include "core/hw/gpu.h"
 #include "core/hw/hw.h"
@@ -151,10 +151,10 @@ void RendererOpenGL::SwapBuffers() {
     render_window->PollEvents();
     render_window->SwapBuffers();
 
-    prev_state.Apply();
+    Core::System::GetInstance().frame_limiter.DoFrameLimiting(CoreTiming::GetGlobalTimeUs());
-
     Core::System::GetInstance().perf_stats.BeginSystemFrame();
 
+    prev_state.Apply();
     RefreshRasterizerSetting();
 
     if (Pica::g_debug_context && Pica::g_debug_context->recorder) {