From a489bff0d191e02828ccddb8d923a828a70a7edf Mon Sep 17 00:00:00 2001
From: Ryan Walters <ryan@walters.to>
Date: Wed, 3 Sep 2025 17:23:20 -0500
Subject: [PATCH] chore: add timing demo bin

---
 Cargo.toml             |  1 +
 src/bin/timing_demo.rs | 91 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+)
 create mode 100644 src/bin/timing_demo.rs

diff --git a/Cargo.toml b/Cargo.toml
index 7614b0d..fcaa510 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,6 +13,7 @@ keywords = ["game", "pacman", "arcade", "sdl2"]
 categories = ["games", "emulators"]
 publish = false
 exclude = ["/assets/unpacked/**", "/assets/site/**", "/bacon.toml", "/Justfile"]
+default-run = "pacman"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
diff --git a/src/bin/timing_demo.rs b/src/bin/timing_demo.rs
new file mode 100644
index 0000000..ad6101d
--- /dev/null
+++ b/src/bin/timing_demo.rs
@@ -0,0 +1,91 @@
+use circular_buffer::CircularBuffer;
+use pacman::constants::CANVAS_SIZE;
+use sdl2::event::Event;
+use sdl2::keyboard::Keycode;
+use sdl2::pixels::Color;
+use std::time::{Duration, Instant};
+
+fn main() -> Result<(), String> {
+    let sdl_context = sdl2::init()?;
+    let video_subsystem = sdl_context.video()?;
+
+    let window = video_subsystem
+        .window("SDL2 Timing Demo", CANVAS_SIZE.x, CANVAS_SIZE.y)
+        .opengl()
+        .position_centered()
+        .build()
+        .map_err(|e| e.to_string())?;
+
+    let mut canvas = window.into_canvas().accelerated().build().map_err(|e| e.to_string())?;
+    canvas
+        .set_logical_size(CANVAS_SIZE.x, CANVAS_SIZE.y)
+        .map_err(|e| e.to_string())?;
+
+    let mut event_pump = sdl_context.event_pump()?;
+
+    // Store frame timings in milliseconds
+    let mut frame_timings = CircularBuffer::<20_000, f64>::new();
+    let mut last_report_time = Instant::now();
+    let report_interval = Duration::from_millis(500);
+
+    'running: loop {
+        let frame_start_time = Instant::now();
+
+        for event in event_pump.poll_iter() {
+            match event {
+                Event::Quit { .. }
+                | Event::KeyDown {
+                    keycode: Some(Keycode::Escape),
+                    ..
+                } => {
+                    break 'running;
+                }
+                _ => {}
+            }
+        }
+
+        // Clear the screen
+        canvas.set_draw_color(Color::RGB(0, 0, 0));
+        canvas.clear();
+        canvas.present();
+
+        // Record timing
+        let frame_duration = frame_start_time.elapsed();
+        frame_timings.push_back(frame_duration.as_secs_f64());
+
+        // Report stats every `report_interval`
+        let elapsed = last_report_time.elapsed();
+        if elapsed >= report_interval {
+            if !frame_timings.is_empty() {
+                let count = frame_timings.len() as f64;
+                let sum: f64 = frame_timings.iter().sum();
+                let mean = sum / count;
+
+                let variance = frame_timings
+                    .iter()
+                    .map(|value| {
+                        let diff = mean - value;
+                        diff * diff
+                    })
+                    .sum::<f64>()
+                    / count;
+                let std_dev = variance.sqrt();
+
+                println!(
+                    "Rendered {count} frames at {fps:.1} fps (last {elapsed:.2?}): mean={mean:.3?}, std_dev={std_dev:.3?}",
+                    count = frame_timings.len(),
+                    fps = count / elapsed.as_secs_f64(),
+                    elapsed = elapsed,
+                    mean = Duration::from_secs_f64(mean),
+                    std_dev = Duration::from_secs_f64(std_dev),
+                );
+            }
+
+            // Reset for next interval
+            frame_timings.clear();
+            last_report_time = Instant::now();
+        }
+    }
+
+    Ok(())
+}