first wrong flake draw

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

@@ -3,17 +3,22 @@ extern crate sdl2;
 use sdl2::pixels::Color;
 use sdl2::event::Event;
 use sdl2::keyboard::Keycode;
+use sdl2::render::Canvas;
+use sdl2::video::Window;
+use sdl2::gfx::primitives::DrawRenderer;
 use std::time::Duration;
 
 struct Base {
     lines: Vec<Line>,
 }
 
+#[derive(Clone, Debug)]
 struct Position {
     x: u32,
     y: u32,
 }
 
+#[derive(Clone, Debug)]
 struct Line {
     start: Position,
     end: Position,
@@ -50,6 +55,10 @@ pub fn main() {
             , end: Position{x: width / 4, y: 3 * height / 4}}
         ]};
 
+    canvas.set_draw_color(Color::RGB(0, 0, 0));
+    canvas.clear();
+    canvas.present();
+
     'running: loop {
         if i % 255 == 0 {
             flip = !flip;
@@ -59,14 +68,18 @@ pub fn main() {
         } else {
             i = i + 1;
         }
-        canvas.set_draw_color(Color::RGB(i, 64, 255 - i));
-        canvas.clear();
+        //canvas.set_draw_color(Color::RGB(i, 64, 255 - i));
+        //canvas.clear();
+        draw_lines(&canvas, Color::RGB(255 - i, 64, i), & base.lines);
         for event in event_pump.poll_iter() {
             match event {
                 Event::Quit { .. } |
                 Event::KeyDown { keycode: Some(Keycode::Escape), .. } => {
                     break 'running
                 },
+                Event::KeyDown { keycode: Some(Keycode::Return), .. } => {
+                    base.lines = step(base.lines);
+                },
                 _ => {}
             }
         }
@@ -75,3 +88,67 @@ pub fn main() {
         ::std::thread::sleep(Duration::from_millis(1000 / 60));
     }
 }
+
+fn step (lines: Vec<Line>) -> Vec<Line> {
+    println!("breaking {:?}", lines);
+    lines.iter().fold(vec![], break_line)
+}
+
+fn break_line (mut acc: Vec<Line>, line: & Line) -> Vec<Line> {
+    let dx = line.end.x as i32 - line.start.x as i32;
+    let dy = line.end.y as i32 - line.start.y as i32;
+    let first = Line{
+        start: Position {
+            x : line.start.x,
+            y : line.start.y,
+        },
+        end: Position {
+            x : (line.start.x as i32 + dx / 3) as u32,
+            y : (line.start.y as i32 + dy / 3) as u32,
+        },
+    };
+    let second = Line{
+        start: Position {
+            x : (line.start.x as i32 + dx / 3) as u32,
+            y : (line.start.y as i32 + dy / 3) as u32,
+        },
+        end: Position {
+            x : line.start.x,
+            y : (line.start.y as i32 + 2 * (dy / 3)) as u32,
+        },
+    };
+    let third = Line{
+        start: Position {
+            x : line.start.x,
+            y : (line.start.y as i32 + 2 * (dy / 3)) as u32,
+        },
+        end: Position {
+            x : (line.start.x as i32 + 2 * (dx / 3)) as u32,
+            y : (line.start.y as i32 + 2 * (dy / 3)) as u32,
+        },
+    };
+    let fourth = Line{
+        start: Position {
+            x : (line.start.x as i32 + 2 * (dx / 3)) as u32,
+            y : (line.start.y as i32 + 2 * (dy / 3)) as u32,
+        },
+        end: Position {
+            x : (line.start.x as i32 + dx) as u32,
+            y : (line.start.y as i32 + dy) as u32,
+        },
+    };
+    acc.append(& mut vec![first, second, third, fourth]);
+    acc.to_vec()
+}
+
+fn draw_lines (canvas: & Canvas<Window>, color: Color, lines: & Vec<Line>) {
+    for line in lines {
+        canvas.line(
+            line.start.x as i16,
+            line.start.y as i16,
+            line.end.x as i16,
+            line.end.y as i16,
+            color
+        ).unwrap();
+    }
+}