Add frametime logging for tracking performance over time

Co-Authored-By: jroweboy <jroweboy@gmail.com>

src/core/perf_stats.cpp

@@ -4,8 +4,14 @@
 
 #include <algorithm>
 #include <chrono>
+#include <iterator>
 #include <mutex>
+#include <numeric>
+#include <sstream>
 #include <thread>
+#include <fmt/format.h>
+#include <fmt/time.h>
+#include "common/file_util.h"
 #include "common/math_util.h"
 #include "core/perf_stats.h"
 #include "core/settings.h"
@@ -15,8 +21,31 @@ using DoubleSecs = std::chrono::duration<double, std::chrono::seconds::period>;
 using std::chrono::duration_cast;
 using std::chrono::microseconds;
 
+// Purposefully ignore the first five frames, as there's a significant amount of overhead in
+// booting that we shouldn't account for
+constexpr std::size_t IgnoreFrames = 5;
+
 namespace Core {
 
+PerfStats::PerfStats(u64 title_id) : title_id(title_id) {}
+
+PerfStats::~PerfStats() {
+    if (!Settings::values.record_frame_times || title_id == 0) {
+        return;
+    }
+
+    std::time_t t = std::time(nullptr);
+    std::ostringstream stream;
+    std::copy(perf_history.begin() + IgnoreFrames, perf_history.begin() + current_index,
+              std::ostream_iterator<double>(stream, "\n"));
+    std::string path = FileUtil::GetUserPath(FileUtil::UserPath::LogDir);
+    // %F Date format expanded is "%Y-%m-%d"
+    std::string filename =
+        fmt::format("{}/{:%F-%H-%M}_{:016X}.csv", path, *std::localtime(&t), title_id);
+    FileUtil::IOFile file(filename, "w");
+    file.WriteString(stream.str());
+}
+
 void PerfStats::BeginSystemFrame() {
     std::lock_guard lock{object_mutex};
 
@@ -27,7 +56,12 @@ void PerfStats::EndSystemFrame() {
     std::lock_guard lock{object_mutex};
 
     auto frame_end = Clock::now();
-    accumulated_frametime += frame_end - frame_begin;
+    const auto frame_time = frame_end - frame_begin;
+    if (current_index < perf_history.size()) {
+        perf_history[current_index++] =
+            std::chrono::duration<double, std::milli>(frame_time).count();
+    }
+    accumulated_frametime += frame_time;
     system_frames += 1;
 
     previous_frame_length = frame_end - previous_frame_end;
@@ -40,6 +74,15 @@ void PerfStats::EndGameFrame() {
     game_frames += 1;
 }
 
+double PerfStats::GetMeanFrametime() {
+    if (current_index <= IgnoreFrames) {
+        return 0;
+    }
+    double sum = std::accumulate(perf_history.begin() + IgnoreFrames,
+                                 perf_history.begin() + current_index, 0);
+    return sum / (current_index - IgnoreFrames);
+}
+
 PerfStatsResults PerfStats::GetAndResetStats(microseconds current_system_time_us) {
     std::lock_guard lock{object_mutex};