1 files changed, 33 insertions, 0 deletions
diff --git a/src/timer.rs b/src/timer.rs
new file mode 100644
index 0000000..f34df8d
--- /dev/null
+++ b/src/timer.rs
@@ -0,0 +1,33 @@
+extern crate sdl2;
+
+use sdl2::TimerSubsystem;
+
+static const FREQUENCY = 1000;
+
+/// Implementation of a timer for managing game ticks.
+pub struct Timer {
+    last_sample: u32,
+    ticks_per_second: u32,
+    ms_per_u64_tick: f64,
+
+    sdl_timer: TimerSubsystem,
+}
+
+impl Timer {
+    /// Create a new timer with the given frequency.
+    pub fn new(ticks_per_second: u32, sdl_timer: TimerSubsystem) -> Timer {
+        let last_sample = sdl_timer.ticks() * tics_per_second / FREQUENCY;
+        let ms_per_u64_tick = 1000.0 / sdl_timer.performance_frequency();
+        Timer { last_sample, ticks_per_second, ms_per_u64_tick, sdl_timer }
+    }
+
+    // TODO: Document this.
+    pub fn update(&mut self) {
+        let ms = self.sdl_timer.ticks();
+        let ticks = ms * self.ticks_per_second / FREQUENCY - self.last_sample;
+
+        if ticks > 0 {
+            self.last_sample += ticks;
+        }
+    }
+}