added gravity and physics

src/main.rs

@@ -1,68 +1,87 @@
-use std::time::Instant;
-const UPDATE_INTERVAL: u32 = 80;
+use std::time::{Duration, Instant};
+const UPDATE_INTERVAL: u32 = 40;
+const DEBUG_LOOP: bool = false;
+
+// a struct made for physics objects
+#[derive(Copy, Clone)]
+struct PhysicsObject {
+	location: [f32; 3],
+	velocity: [f32; 3]
+}
 
 fn main() {
     // track the delta time (the duration of the previous loop in milliseconds)
-    let mut delta_time: u32 = 0;
+    let mut delta_time = Duration::new(0, 0);
 
-    // allow for interpolation
+    // create a test physics object
+    let mut test_object = PhysicsObject {
+        location: [0.0, 0.0, 0.0],
+        velocity: [0.0, 0.0, 0.0]
+    };
 
     loop {
-        // start per-loop delay timer
-        let timer = Instant::now();
+        // start timing the loop
+        let start_time = Instant::now();
 
         // update
-        if delta_time >= UPDATE_INTERVAL {
+        if delta_time.as_millis() as u32 >= UPDATE_INTERVAL {
+            if DEBUG_LOOP {
                 println!("Updating");
-            update();
-
-            // DEBUG
+            }
+            update(delta_time, &mut test_object);
 
             // reset the delta time
-            delta_time = timer.elapsed().as_millis() as u32;
+            delta_time = Instant::now().duration_since(start_time);
         }
 
         // support interpolation via fractional "relative time"
-        let relative_time: f32 = delta_time as f32 / UPDATE_INTERVAL as f32;
+        let relative_time: f32 = delta_time.as_millis() as f32 / UPDATE_INTERVAL as f32;
 
-        println!("Displaying | Delta Time: {}ms | Relative Time: {}", delta_time, relative_time);
-        display();
+        if DEBUG_LOOP {
+            println!("Displaying | Delta Time: {}ms | Relative Time: {}", delta_time.as_millis(), relative_time);
+        }
+        display(relative_time, &test_object);
 
-        // update the delta time
-        let elapsed_time: u32 = timer.elapsed().as_millis() as u32;
-        delta_time += elapsed_time;
+        // update the time
+        delta_time += Instant::now().duration_since(start_time);
     }
 }
 
 // update function
 // TODO - I think I'm resetting delta time in the wrong place or just using it incorrectly; frameskips aren't happening at all
-fn update() {
-    waste_time(64);
+fn update(delta_time: Duration, object: &mut PhysicsObject) {
+    // calculate the exact timestep (fractional time in seconds) from delta time
+    let timestep: f32 = delta_time.as_millis() as f32 / 1000.0;
+    println!("Timestep: {}", timestep);
+
+    // gravity
+    let acceleration: [f32; 3] = [0.0, 0.0, -9.8];
+
+    // update velocity based on acceleration (specifically gravity)
+    for i in 0..3 {
+        object.velocity[i] += acceleration[i] * timestep;
+    }
+
+    // update location based on velocity
+    for i in 0..3 {
+        object.location[i] += object.velocity[i];
+    }
 }
 
 // render function
-fn display() {
-    waste_time(4);
+fn display(interpolation: f32, object: &PhysicsObject) {
+    // create a "render object", which we can apply interpolation to
+    let mut render_object = *object;
+
+    // interpolate physics values for smooth rendering
+    for i in 0..3 {
+        render_object.location[i] += render_object.velocity[i] * interpolation;
+    }
+
+    println!("Object location: {:?}", render_object.location);
 }
 
 // 1D linear interpolation
 fn lerp_1d(x: f64, y: f64, a: f64) -> f64 {
     x + ((y - x) * a)
 }
-
-// busywork function
-fn waste_time(repeat: u32) {
-    const BUFFER_RESOLUTION: usize = 512;
-    
-    // create an RGBA buffer and change every pixel one-by-one
-    let mut rgba_buffer = vec![[[0.0f32; 4]; BUFFER_RESOLUTION]; BUFFER_RESOLUTION];
-
-    // change every pixel in the buffer (repeat) times
-    for _n in 0..repeat {
-        for u in 0..BUFFER_RESOLUTION {
-            for v in 0..BUFFER_RESOLUTION {
-                rgba_buffer[u][v] = [1.0f32; 4];
-            }
-        }
-    }
-}