initial commit

Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "egui-circles"
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.56"
+
+[dependencies]
+eframe = "0.24.0" # Gives us egui, epi and web+native backends
+emath  = "0.24.0"
+rand = "0.8"

src/circle.rs

@@ -0,0 +1,58 @@
+pub mod circle {
+
+    use emath::Vec2;
+    use emath::Pos2;
+    use emath::Rect;
+    use rand::Rng;
+
+    pub static FRICTION: f32 = 0.995;
+
+    pub struct Circle {
+        pub v: Vec2,
+        pub c: Pos2,
+        pub r: f32,
+    }
+
+    impl Default for Circle {
+        fn default() -> Self {
+            let r = rand::thread_rng().gen_range(20.0..50.0);
+            Self {
+                r: r,
+                c: Pos2 {
+                    x: rand::thread_rng().gen_range(r..400.0-r),
+                    y: rand::thread_rng().gen_range(r..400.0-r)},
+                v: Vec2 {
+                    x: rand::thread_rng().gen_range(-2.0..2.0),
+                    y: rand::thread_rng().gen_range(-2.0..2.0)},
+            }
+        }
+    }
+
+    impl Circle {
+        pub fn apply_force(&mut self, bb: &Rect) {
+            self.v *= FRICTION;
+            self.c += self.v;
+
+            if self.v.x > 0.0 {
+                if self.c.x + self.r > bb.right() {
+                    self.v.x *= -1.0
+                }
+            } else  {
+                if self.c.x - self.r < bb.left() {
+                    self.v.x *= -1.0
+                }
+            }
+
+            if self.v.y > 0.0 {
+                if self.c.y + self.r > bb.bottom() {
+                    self.v.y *= -1.0
+                }
+            } else  {
+                if self.c.y - self.r < bb.top() {
+                    self.v.y *= -1.0
+                }
+            }
+        }
+    }
+}
+

src/main.rs

@@ -0,0 +1,182 @@
+use emath::Vec2;
+use eframe::egui;
+use egui::Color32;
+use egui::Stroke;
+use rand::Rng;
+
+mod circle;
+pub use circle::circle::Circle;
+
+struct ExampleApp {
+    circles: Vec<Circle>,
+    circles_count: usize,
+
+    colors: Vec<egui::Color32>,
+}
+
+impl ExampleApp {
+    fn name() -> &'static str {
+        "egui-circles"
+    }
+}
+
+impl Default for ExampleApp {
+    fn default() -> Self {
+        Self {
+            circles: Vec::new(),
+            circles_count: 2,
+            colors: Vec::new(),
+        }
+    }
+}
+
+impl eframe::App for ExampleApp {
+    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        // Looks better on 4k montior
+        ctx.set_pixels_per_point(1.5);
+
+        egui::CentralPanel::default().show(ctx, |ui| {
+            if ui.button("halt").clicked() {
+                //frame.quit()
+                self.circles.iter_mut().for_each(|c| (*c).v = Vec2{x: 0.0, y: 0.0});
+            };
+
+            if ui.button("push").clicked() {
+                self.circles.iter_mut().for_each(|c| (*c).v = Vec2{
+                    x: rand::thread_rng().gen_range(-2.0..2.0),
+                    y: rand::thread_rng().gen_range(-2.0..2.0)});
+            };
+
+
+            ui.add(egui::Slider::new(&mut self.circles_count, 0..=25).text("circles count"));
+            let diff = (self.circles.len() as i32) - (self.circles_count as i32);
+            if diff > 0 {
+                self.circles.truncate(self.circles_count);
+            } else {
+                for _ in diff..0 {
+                    self.circles.push(Circle::default());
+                    self.colors.push(
+                        egui::Color32::from_rgba_premultiplied(
+                            rand::thread_rng().gen_range(0..255),
+                            rand::thread_rng().gen_range(0..255),
+                            rand::thread_rng().gen_range(0..255),
+                            64)
+                        );
+                }
+            }
+
+            let painter = ui.painter();
+
+            let (hover_pos, any_down, any_released) = ctx.input(|input| (input.pointer.hover_pos(), input.pointer.any_down(), input.pointer.any_released()));
+
+            if let Some(mousepos) = hover_pos {
+                
+                self.circles.iter_mut().for_each(|circle|{
+                    let d = (*circle).c - mousepos;    
+                    if d.length() < (*circle).r {             
+                        if any_down {
+                            painter.line_segment(
+                            [(*circle).c, (*circle).c +d], 
+                                Stroke{width: 1.0, color: Color32::from_rgb(128, 255, 255)});
+                        }
+
+                        if any_released {
+                            (*circle).v += d.normalized() * (d.length() / (*circle).r) *8.0;
+                        }
+                    }
+                });
+            }
+
+            for i in 0..self.circles_count {
+                painter.circle(
+                    self.circles[i].c, 
+                    self.circles[i].r, 
+                self.colors[i] /*Color32::TRANSPARENT*/, 
+                    Stroke{width: 2.0, color: Color32::from_rgb(255, 255, 255)}
+                );
+            }
+        });
+
+        for circle in &mut self.circles {
+            (*circle).apply_force(&ctx.used_rect());
+        }
+
+        // Naive N^2 Colition detection
+        // Optimization https://en.wikipedia.org/wiki/Sweep_and_prune
+        for i in 0..self.circles_count {
+            for j in i+1..self.circles_count {
+
+                if (i + j) % 3 == 0 {
+                    continue;   // skip collsions for every third ball
+                }
+
+                let dc = self.circles[i].c - self.circles[j].c;
+                let dr = self.circles[i].r + self.circles[j].r;
+
+                if dc.length() < dr {
+                    (self.circles[i].v, self.circles[j].v) = collision(&self.circles[i], &self.circles[j]);
+                }
+            }
+        }
+
+        // This is how to go into continuous mode - uncomment this to see example of continuous mode
+        ctx.request_repaint();
+    }
+}
+
+fn main() -> eframe::Result<()> {
+    let native_options = eframe::NativeOptions {
+        viewport: egui::ViewportBuilder::default().with_inner_size((800.0, 600.0)),
+        ..eframe::NativeOptions::default()
+    };
+
+    eframe::run_native(
+        ExampleApp::name(),
+        native_options,
+        Box::new(|_| Box::<ExampleApp>::default()),
+    )
+}
+
+fn collision(c1: &Circle, c2: &Circle) -> (Vec2, Vec2) {
+    let m1 = c1.r;
+    let m2 = c2.r;
+
+    // collision normal
+    let n = Vec2{
+        x: c2.c.x - c1.c.x, 
+        y: c2.c.y - c1.c.y
+    };
+
+    // normal vector unit
+    let un = n.normalized();
+
+    // collision tangen
+    let ut = Vec2{x: -un.y, y: un.x};
+
+    // 3
+    let v1n = un.dot(c1.v);
+    let v1t = ut.dot(c1.v);
+
+    let v2n = un.dot(c2.v);
+    let v2t = ut.dot(c2.v);
+
+    // 4
+    let v1t_new = v1t;
+    let v2t_new = v2t;
+
+    // 5
+    let v1n_new = (v1n * (m1 - m2) + 2.0 * m2 * v2n) / (m1 + m2);
+    let v2n_new = (v2n * (m2 - m1) + 2.0 * m1 * v1n) / (m1 + m2);
+
+    // 6
+    let vec1n = v1n_new * un;
+    let vec1t = v1t_new * ut;
+
+    let vec2n = v2n_new * un;
+    let vec2t = v2t_new * ut;
+
+    return ( 
+        vec1n + vec1t,
+        vec2n + vec2t
+    );
+}