From 7e8ee5ed9cad6484e9f13f81731b102ced58402e Mon Sep 17 00:00:00 2001
From: Adam Carpenter <gitlab@53hor.net>
Date: Tue, 9 Jul 2019 15:14:04 -0400
Subject: Init.

---
 meap/meap-code/ch6/ch6-particles/src/main.rs | 170 +++++++++++++++++++++++++++
 1 file changed, 170 insertions(+)
 create mode 100755 meap/meap-code/ch6/ch6-particles/src/main.rs

(limited to 'meap/meap-code/ch6/ch6-particles/src/main.rs')

diff --git a/meap/meap-code/ch6/ch6-particles/src/main.rs b/meap/meap-code/ch6/ch6-particles/src/main.rs
new file mode 100755
index 0000000..93696fb
--- /dev/null
+++ b/meap/meap-code/ch6/ch6-particles/src/main.rs
@@ -0,0 +1,170 @@
+// #![feature(alloc_system, global_allocator, allocator_api)]
+
+// extern crate alloc_system;
+
+// use alloc_system::System;
+
+// #[global_allocator]
+// static A: System = System;
+
+extern crate graphics;
+extern crate piston_window;
+extern crate rand;
+
+use graphics::math::{ Vec2d, add, mul_scalar };
+use piston_window::{ PistonWindow, WindowSettings, clear, rectangle };
+use rand::distributions::{IndependentSample, Range};
+
+type RGBA = [f32; 4];
+const WHITE: RGBA = [1.0; 4];
+const GRAY: RGBA  = [0.7, 0.7, 0.7, 0.3];
+const N_PARTICLES: usize = 500;
+
+struct World {
+    current_turn: usize,
+    shapes: Vec<Box<Shape>>,
+    height: u32,
+    width: u32,
+}
+
+struct Shape {
+    height: f64,
+    width: f64,
+    position: Vec2d<f64>,
+    velocity: Vec2d<f64>,
+    acceleration: Vec2d<f64>,
+    color: RGBA,
+}
+
+impl Shape {
+    fn new(x: f64, y: f64) -> Self {
+        let mut rng = rand::thread_rng();
+        let legal_range = Range::new(-5_f64, 5_f64);
+
+        let x_speed = legal_range.ind_sample(&mut rng);
+        let y_speed = legal_range.ind_sample(&mut rng);
+        let x_accel = 0.1 * legal_range.ind_sample(&mut rng);
+        let y_accel = 0.1 * legal_range.ind_sample(&mut rng);
+
+        Shape {
+            height: 10.0,
+            width: 10.0,
+            position: [x, y],
+            velocity: [x_speed, y_speed],
+            acceleration: [x_accel, y_accel],
+            color: GRAY,
+        }
+    }
+
+    fn update(&mut self) {
+        self.velocity = add(self.velocity, self.acceleration); // <> There is no matrix/vector math operators within the language. `graphics::math` is providing this functionality for us.  
+        self.position = add(self.position, self.velocity); 
+        self.acceleration = mul_scalar(self.acceleration, 0.7); // <> Slow down the shape's movement
+        self.color[3] *= 0.97; 
+    }
+}
+
+impl World {
+    fn new(width: u32, height: u32) -> World {
+        World {
+            current_turn: 0,
+            shapes: Vec::<Box<Shape>>::new(),
+            height: height,
+            width: width,
+        }
+    }
+
+    fn add_shapes(&mut self, n: usize) {
+        let x = (self.width / 2) as f64;
+        let y = (self.height / 2) as f64;
+
+        for _ in 0..n {
+            self.shapes.push(Box::new(Shape::new(x, y)));
+        };
+    }
+
+    fn remove_shapes(&mut self, n: usize) {
+        let n_shapes = self.shapes.len();
+
+        let to_remove = if n > n_shapes {
+            n_shapes
+        } else {
+            n
+        };
+        // let to_remove = cmp::min(n as usize, self.shapes.len());
+
+        for _ in 0..to_remove {
+            self.shapes.remove(0); // Remove the oldest particle. This is quite an inefficient operation, as all remaining particles are shifted to fill the now-empty slot. A smarter strategy would be to use `std::collections::VecDeque`, which supports removing from the front.
+        }
+
+        self.shapes.shrink_to_fit(); // Will help to force a re-allocation later when shapes are added.
+    }
+
+    fn calc_population_change(&self) -> isize {
+        const N: f64 = N_PARTICLES as f64; // <> Shorter alias
+        const MAX: f64 =  N*0.5;
+        const MIN: f64 = -N*0.5;
+        let x: f64 = self.current_turn as f64;
+
+        //let n: f64 = N_PARTICLES;
+        let n = 0.4*N*(0.1*x).sin() + 0.1*N*x.sin();
+        n.max(MIN).min(MAX).round() as isize // limit range of growth/death then convert to `isize`
+    }
+
+    fn update(&mut self) {
+        let n = self.calc_population_change();
+        //let n = as usize; // <> Convert f64 to usize
+
+        if n > 0 {
+            self.add_shapes(n as usize);
+        } else {
+            self.remove_shapes(n.abs() as usize);
+        }
+
+        self.current_turn += 1;
+    }
+} 
+
+// impl Iterator for World {
+//     type Item = isize;
+
+//     fn next(&mut self) -> Option<isize> {
+//         let x = self.current_turn;
+
+//         //  30sin(x) + 10sin(0.1x) + 20sin(0.2x)  + 30sin(0.3x)  + 40sin(0.4x)   + 50sin(0.5x)  
+//         let y = 50.0*(0.1*x).sin() + 30.0*x.sin();
+//         self.current_turn += 1.0;
+//         Some(y.round() as isize)
+//     }
+// }
+
+fn main() {
+    let (width, height) = (640, 480);
+    let mut window: PistonWindow = 
+                        WindowSettings::new("particles", [width, height])
+                        .exit_on_esc(true)
+                        .build()
+                        .expect("Could not create a window.");
+    
+    // Initialize
+    let mut world = World::new(width, height);
+    world.add_shapes(N_PARTICLES);
+
+    while let Some(event) = window.next() { // main loop
+        // Update Step
+        for shape in &mut world.shapes {
+            shape.update();
+        }
+        world.update();
+
+        // Render Step
+        window.draw_2d(&event, |ctx, renderer| {
+            clear(WHITE, renderer);
+            for s in &mut world.shapes {
+                let rect = [s.position[0], s.position[1], s.width, s.height];
+                let transformation_matrix = ctx.transform; 
+                rectangle(s.color, rect, transformation_matrix, renderer); // create a graphics::Rectangle and call draw() on it
+            }
+        });
+    }
+}
-- 
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