Data commit

Task/Animate-a-pendulum/Rust/animate-a-pendulum.rust

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+// using version 0.107.0 of piston_window
+use piston_window::{clear, ellipse, line_from_to, PistonWindow, WindowSettings};
+
+const PI: f64 = std::f64::consts::PI;
+const WIDTH: u32 = 640;
+const HEIGHT: u32 = 480;
+
+const ANCHOR_X: f64 = WIDTH as f64 / 2. - 12.;
+const ANCHOR_Y: f64 = HEIGHT as f64 / 4.;
+const ANCHOR_ELLIPSE: [f64; 4] = [ANCHOR_X - 3., ANCHOR_Y - 3., 6., 6.];
+
+const ROPE_ORIGIN: [f64; 2] = [ANCHOR_X, ANCHOR_Y];
+const ROPE_LENGTH: f64 = 200.;
+const ROPE_THICKNESS: f64 = 1.;
+
+const DELTA: f64 = 0.05;
+const STANDARD_GRAVITY_VALUE: f64 = -9.81;
+
+// RGBA Colors
+const BLACK: [f32; 4] = [0., 0., 0., 1.];
+const RED: [f32; 4] = [1., 0., 0., 1.];
+const GOLD: [f32; 4] = [216. / 255., 204. / 255., 36. / 255., 1.0];
+fn main() {
+    let mut window: PistonWindow = WindowSettings::new("Pendulum", [WIDTH, HEIGHT])
+        .exit_on_esc(true)
+        .build()
+        .unwrap();
+
+    let mut angle = PI / 2.;
+    let mut angular_vel = 0.;
+
+    while let Some(event) = window.next() {
+        let (angle_sin, angle_cos) = angle.sin_cos();
+        let ball_x = ANCHOR_X + angle_sin * ROPE_LENGTH;
+        let ball_y = ANCHOR_Y + angle_cos * ROPE_LENGTH;
+
+        let angle_accel = STANDARD_GRAVITY_VALUE / ROPE_LENGTH * angle_sin;
+        angular_vel += angle_accel * DELTA;
+        angle += angular_vel * DELTA;
+        let rope_end = [ball_x, ball_y];
+        let ball_ellipse = [ball_x - 7., ball_y - 7., 14., 14.];
+
+        window.draw_2d(&event, |context, graphics, _device| {
+            clear([1.0; 4], graphics);
+            line_from_to(
+                BLACK,
+                ROPE_THICKNESS,
+                ROPE_ORIGIN,
+                rope_end,
+                context.transform,
+                graphics,
+            );
+            ellipse(RED, ANCHOR_ELLIPSE, context.transform, graphics);
+            ellipse(GOLD, ball_ellipse, context.transform, graphics);
+        });
+    }
+}