From d7354cca336d0a705b224e5cedb74f526dac4224 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 21 Oct 2022 05:12:27 -0300
Subject: [PATCH] chore: improve accuracy of frame limiter

---
 src/emu.zig  | 40 +++++++++++++++++++++++++++-------------
 src/main.zig |  2 +-
 src/util.zig |  2 +-
 3 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/src/emu.zig b/src/emu.zig
index f4fb969..7489e5a 100644
--- a/src/emu.zig
+++ b/src/emu.zig
@@ -49,28 +49,42 @@ pub fn runEmuThread(quit: *Atomic(bool), pause: *Atomic(bool), fps: *Atomic(u64)
             // ns_late is non zero if we are late.
             var ns_late = timestamp -| wake_time;
 
-            // Calculate the new Thread wake time
-            wake_time += frame_period;
+            // log.info("timestamp: {} | late: {}", .{ timestamp, ns_late });
 
             // If we're more than a frame late, skip the rest of this loop
-            if (ns_late > frame_period) continue;
+            // Recalculate what our new wake time should be so that we can
+            // get "back on track"
+            if (ns_late > frame_period) {
+                wake_time = timestamp + frame_period;
+                continue;
+            }
 
-            if (sync_to_video) std.time.sleep(frame_period - ns_late);
+            if (sync_to_video) {
+                // Employ several sleep calls in periods of 10ms
+                // By doing this the behaviour should average out to be
+                // more consistent
 
-            // Backup Busy Loop Routine
-            // if (sync_to_video) spinLoop(&timer, wake_time);
+                const sleep_for = frame_period - ns_late;
+                const loop_count = sleep_for / (std.time.ns_per_ms * 10); // How many groups of 10ms
+
+                var i: usize = 0;
+                while (i < loop_count) : (i += 1) {
+                    std.time.sleep(std.time.ns_per_ms * 10);
+                }
+
+                // Spin to make up the difference if there is a need
+                // Make sure that we're using the old wake time and not the onne we recalcualted
+                spinLoop(&timer, wake_time);
+            }
+
+            // Update to the new wake time
+            wake_time += frame_period;
         }
     }
 }
 
 fn spinLoop(timer: *Timer, wake_time: u64) void {
-    while (true) {
-        const timestamp = timer.read();
-
-        if (timestamp >= wake_time) {
-            break;
-        }
-    }
+    while (true) if (timer.read() > wake_time) break;
 }
 
 fn emuFps(left: u64) u64 {
diff --git a/src/main.zig b/src/main.zig
index 767f8ab..79beee9 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -177,7 +177,7 @@ pub fn main() anyerror!void {
         fps_avg.add(emu_fps.load(.Unordered));
         const avg = fps_avg.calc();
 
-        const dyn_title = std.fmt.bufPrint(&dyn_title_buf, "{s} [Emu: {d:0>3}fps, {d:0>3}%] ", .{ title, avg, (avg * 100 / 59) }) catch unreachable;
+        const dyn_title = std.fmt.bufPrint(&dyn_title_buf, "{s} [Emu: {d:0>3}fps, {d:0>3}%] ", .{ title, avg, (avg * 100 / 60) }) catch unreachable;
         SDL.SDL_SetWindowTitle(window, dyn_title.ptr);
     }
 
diff --git a/src/util.zig b/src/util.zig
index 05568a8..6e3db87 100644
--- a/src/util.zig
+++ b/src/util.zig
@@ -18,7 +18,7 @@ pub const FpsAverage = struct {
     }
 
     pub fn add(self: *Self, sample: u64) void {
-        if (self.sample_count == 1000) return self.reset(sample);
+        if (self.sample_count == 600) return self.reset(sample);
 
         self.total += sample;
         self.sample_count += 1;