Count frames more precisely

Instead of calculating the time from the beginning, we'll just check the
time since the frame was started. This means if you are slow and then
fast, it won't freak out.

This was inspired by an app I wrote for Clank which counts clanks frame
by frame and I needed some similar mechanism.

1 files changed, 3 insertions, 5 deletions

diff --git a/src/main.rs b/src/main.rs
index 6e1322a..9089daf 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -84,9 +84,7 @@ fn main() {
     canvas.clear();
     canvas.present();
     let mut event_pump = sdl_context.event_pump().unwrap();
-    let start = std::time::Instant::now();
     let frame_duration = std::time::Duration::new(0, 1_000_000_000u32 / 60);
-    let mut frame_count = 0;
     let mut state: state::State<gates::Gates, gates::GatesBullet> = state::State::new();
     let mut won = false;
     let player_surface: sdl2::surface::Surface = sdl2::image::LoadSurface::from_file("assets/stallman.png").unwrap();
@@ -100,6 +98,7 @@ fn main() {
     let pbullet_texture = texture_creator.create_texture_from_surface(pbullet_surface).unwrap();
     let surfaces = Textures { player: player_texture, enemy: enemy_texture, pbullet: pbullet_texture, ebullet: ebullet_texture };
     'running: loop {
+        let start = std::time::Instant::now();
         if won {
             for event in event_pump.poll_iter() {
                 match event {
@@ -127,11 +126,10 @@ fn main() {
                 }
             }
         }
-        let calc_time = frame_duration * frame_count;
-        match calc_time.checked_sub(start.elapsed()) {
+        /* Make sure this iteration took a whole frame */
+        match frame_duration.checked_sub(start.elapsed()) {
             Some(t) => std::thread::sleep(t),
             None => (),
         }
-        frame_count += 1;
     }
 }