Koch snowflake

Cargo.lock

@@ -8,6 +8,12 @@ version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
 
+[[package]]
+name = "c_vec"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fdd7a427adc0135366d99db65b36dae9237130997e560ed61118041fb72be6e8"
+
 [[package]]
 name = "cfg-if"
 version = "1.0.0"
@@ -40,6 +46,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3b498da7d14d1ad6c839729bd4ad6fc11d90a57583605f3b4df2cd709a9cd380"
 dependencies = [
  "bitflags",
+ "c_vec",
  "lazy_static",
  "libc",
  "sdl2-sys",

Cargo.toml

@@ -6,4 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-sdl2 = "0.37"
+sdl2 = { version = "0.37", features = ["gfx"] }

flake.nix

@@ -16,6 +16,7 @@
 
         packageBuildInputs = with pkgs; [
           SDL2
+          SDL2_gfx
         ];
 
         inherit (import "${crate2nix}/tools.nix" { inherit pkgs; })

src/main.rs

@@ -1,50 +1,133 @@
 extern crate sdl2;
 
-use sdl2::pixels::Color;
+use std::cmp::min;
+
 use sdl2::event::Event;
 use sdl2::keyboard::Keycode;
-use std::time::Duration;
+use sdl2::pixels::{self, Color};
 
-pub fn main() {
-    println!("Hello, world!");
-    let sdl_context = sdl2::init().unwrap();
-    let video_subsystem = sdl_context.video().unwrap();
+use sdl2::gfx::primitives::DrawRenderer;
+use sdl2::render::WindowCanvas;
 
-    let window = match video_subsystem.window("fractals", 800, 600)
+const SCREEN_WIDTH: i16 = 800;  // i15
+const SCREEN_HEIGHT: i16 = 600;  // i15
+
+fn atan(a: f32, b: f32) -> f32 {
+    if b == 0.0 {
+        return 0.0
+    } else if b < 0.0 {
+        return (a/b).atan() + std::f32::consts::PI;
+    } else {
+        return (a/b).atan();
+    }
+}
+
+/** for each zoomlevel, lines are replaced by 4 new lines of length a/3 **/
+fn koch_line(canvas: &WindowCanvas, x0: i16, y0: i16, x4: i16, y4: i16, color: Color, zoom: i16) {
+
+  if zoom == 1 {
+      let _ = canvas.line(x0, y0, x4, y4, color);
+  } else {
+      /* the outer two lines */
+      let x1 = x0 + (x4-x0) / 3;
+      let y1 = y0 + (y4-y0) / 3;
+      let x3 = x0 + 2* (x4-x0) / 3;
+      let y3 = y0 + 2* (y4-y0) / 3;
+      koch_line(canvas, x0, y0, x1, y1, color, zoom-1);
+      koch_line(canvas, x3, y3, x4, y4, color, zoom-1);
+
+      /* the inner two lines (arms of an equilateral triangle) */
+      let dx = x3 - x1;
+      let dy = y3 - y1;
+      let a = ((dx*dx + dy*dy) as f32).sqrt();
+      let angle = atan((-dy).into(), dx.into());  // angle of the original line 
+      const INTERNAL_ANGLE: f32 = std::f32::consts::FRAC_PI_3;  // 60_f32.to_radians();
+      let x2 = x1 + ((a * (angle - INTERNAL_ANGLE).cos()) as i16);
+      let y2 = y1 - ((a * (angle - INTERNAL_ANGLE).sin()) as i16);
+      koch_line(canvas, x1, y1, x2, y2, color, zoom-1);
+      koch_line(canvas, x2, y2, x3, y3, color, zoom-1);
+  }
+}
+
+fn koch_snowflake(canvas: &WindowCanvas, x: i16, y: i16, a: i16, color: Option<Color>, zoom: i16) {
+    let max_zoom = (a as f32).log(3.0).ceil() as i16;
+    let effective_zoom = min(zoom, max_zoom);
+    println!("zoom: {}/{}", effective_zoom, max_zoom);
+
+    let c = (255 * (effective_zoom-1) / (max_zoom-1)) as u8;
+    let color = color.unwrap_or(Color::RGB(c, c, 127+c/2));
+
+    let h = (a as f32 * 3.0_f32.sqrt() / 2.0) as i16;  // height of equilateral triangle
+
+    let x1 = x;
+    let y1 = y - h/2;
+    let x2 = x - a/2;
+    let y2 = y + h/2;
+    let x3 = x + a/2;
+    let y3 = y + h/2;
+    koch_line(&canvas, x1, y1, x2, y2, color, effective_zoom);
+    koch_line(&canvas, x2, y2, x3, y3, color, effective_zoom);
+    koch_line(&canvas, x3, y3, x1, y1, color, effective_zoom);
+}
+
+fn main() -> Result<(), String> {
+    let sdl_context = sdl2::init()?;
+    let video_subsys = sdl_context.video()?;
+    let window = video_subsys
+        .window(
+            "rust-sdl2_gfx: draw line & FPSManager",
+            (SCREEN_WIDTH as u16).into(),
+            (SCREEN_HEIGHT as u16).into(),
+        )
         .position_centered()
-        .build() {
-            Ok(w) => { w },
-            Err(_)  => { panic!("Can not build window!") }
-        };
+        .opengl()
+        .build()
+        .map_err(|e| e.to_string())?;
 
-    let mut canvas = window.into_canvas().build().unwrap();
+    let mut canvas = window.into_canvas().build().map_err(|e| e.to_string())?;
 
-    let mut event_pump = sdl_context.event_pump().unwrap();
-    let mut i = 0;
-    let mut flip = true;
+    canvas.set_draw_color(pixels::Color::RGB(0, 0, 0));
+    canvas.clear();
+    canvas.present();
+    println!("Welcome :)");
+    println!("[Klick] into canvas to draw a koch snowflake…");
+    println!("Press [Space] to clear the canvas…");
+    println!("Press [Backspace] to reset the zoom…");
 
-    'running: loop {
-        if i % 255 == 0 {
-            flip = !flip;
-        }
-        if flip && i > 0 {
-            i = i - 1;
-        } else {
-            i = i + 1;
-        }
-        canvas.set_draw_color(Color::RGB(i, 64, 255 - i));
-        canvas.clear();
-        for event in event_pump.poll_iter() {
+    let mut events = sdl_context.event_pump()?;
+
+    let mut zoom = 1;
+
+    'main: loop {
+        for event in events.poll_iter() {
             match event {
-                Event::Quit { .. } |
-                Event::KeyDown { keycode: Some(Keycode::Escape), .. } => {
-                    break 'running
-                },
+                Event::Quit { .. } => break 'main,
+
+                Event::KeyDown {
+                    keycode: Some(keycode),
+                    ..
+                } => {
+                    if keycode == Keycode::Escape {
+                        break 'main;
+                    } else if keycode == Keycode::Space {
+                        canvas.set_draw_color(pixels::Color::RGB(0, 0, 0));
+                        canvas.clear();
+                        canvas.present();
+                    } else if keycode == Keycode::BACKSPACE {
+                        zoom = 1
+                    }
+                }
+
+                Event::MouseButtonDown { x, y, .. } => {
+                    koch_snowflake(&canvas, x.try_into().unwrap(), y.try_into().unwrap(), SCREEN_HEIGHT/3, None, zoom);
+                    canvas.present();
+                    zoom += 1;
+                }
+
                 _ => {}
             }
         }
-
-        canvas.present();
-        ::std::thread::sleep(Duration::from_millis(1000 / 60));
     }
+
+    Ok(())
 }