Add trace image generator

.gitignore

@@ -1,3 +1,4 @@
 /target
 *.csv
 *.wav
+*.png

Cargo.lock

@@ -14,6 +14,18 @@ version = "0.2.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
 
+[[package]]
+name = "arrayref"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76a2e8124351fda1ef8aaaa3bbd7ebbcb486bbcd4225aca0aa0d84bb2db8fecb"
+
+[[package]]
+name = "arrayvec"
+version = "0.7.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3fb67a6e08acf24fdeccbac2cb6ac4305825bd1f117462e0e6f2f193345ad56"
+
 [[package]]
 name = "autocfg"
 version = "1.5.1"
@@ -26,6 +38,12 @@ version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
 
+[[package]]
+name = "bitflags"
+version = "2.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ded4057c258ba199e2d26386d3af3780957ecaee6c4ef4041c6b4b8b97c0b06"
+
 [[package]]
 name = "bytemuck"
 version = "1.25.2"
@@ -68,13 +86,6 @@ dependencies = [
  "cfg-if",
 ]
 
-[[package]]
-name = "dpsim"
-version = "0.1.0"
-dependencies = [
- "macroquad",
-]
-
 [[package]]
 name = "equivalent"
 version = "1.0.3"
@@ -144,7 +155,7 @@ dependencies = [
  "byteorder",
  "color_quant",
  "num-traits",
- "png",
+ "png 0.17.16",
 ]
 
 [[package]]
@@ -159,6 +170,12 @@ version = "0.2.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6d2cec3eae94f9f509c767b45932f1ada8350c4bdb85af2fcab4a3c14807981"
 
+[[package]]
+name = "log"
+version = "0.4.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f9f8bd3e56ce4dfc153cf470fffbfa98c7620958b312ca5c3a4b8d5181fd13c6"
+
 [[package]]
 name = "macroquad"
 version = "0.4.16"
@@ -250,7 +267,20 @@ version = "0.17.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "82151a2fc869e011c153adc57cf2789ccb8d9906ce52c0b39a6b5697749d7526"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
+ "crc32fast",
+ "fdeflate",
+ "flate2",
+ "miniz_oxide 0.8.9",
+]
+
+[[package]]
+name = "png"
+version = "0.18.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60769b8b31b2a9f263dae2776c37b1b28ae246943cf719eb6946a1db05128a61"
+dependencies = [
+ "bitflags 2.13.2",
  "crc32fast",
  "fdeflate",
  "flate2",
@@ -269,6 +299,46 @@ version = "0.3.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3a219298ac11a56ea9a6d2120044824d6f01aeb034955e7af7bc16858527deea"
 
+[[package]]
+name = "strict-num"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6637bab7722d379c8b41ba849228d680cc12d0a45ba1fa2b48f2a30577a06731"
+
+[[package]]
+name = "symplectic-double-pendulum"
+version = "0.1.0"
+dependencies = [
+ "macroquad",
+ "tiny-skia",
+]
+
+[[package]]
+name = "tiny-skia"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47ffee5eaaf5527f630fb0e356b90ebdec84d5d18d937c5e440350f88c5a91ea"
+dependencies = [
+ "arrayref",
+ "arrayvec",
+ "bytemuck",
+ "cfg-if",
+ "log",
+ "png 0.18.1",
+ "tiny-skia-path",
+]
+
+[[package]]
+name = "tiny-skia-path"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "edca365c3faccca67d06593c5980fa6c57687de727a03131735bb85f01fdeeb9"
+dependencies = [
+ "arrayref",
+ "bytemuck",
+ "strict-num",
+]
+
 [[package]]
 name = "ttf-parser"
 version = "0.25.1"

Cargo.toml

@@ -5,3 +5,4 @@ edition = "2024"
 
 [dependencies]
 macroquad = "0.4.16"
+tiny-skia = "0.12.0"

README.md

@@ -17,6 +17,13 @@ the simulation can be ran with:
 cargo run --bin anim
 ```
 
+Alternatively you can generate a trace image of the path the outer bob
+takes with:
+
+```
+cargo run --bin trace
+```
+
 ## License
 
 Copyright © Camden Dixie O'Brien, available under the Komorebi 2.0.0

src/bin/trace.rs

@@ -0,0 +1,58 @@
+use symplectic_double_pendulum::*;
+
+use tiny_skia::*;
+
+const WIDTH: u32 = 800;
+const HEIGHT: u32 = 800;
+
+const MIN: f32 = -2.0;
+const MAX: f32 = 2.0;
+const MARGIN: f32 = 0.2;
+
+fn system_xy(q: &DoublePendulum) -> [f64; 2] {
+	[
+		q.theta.sin() + (q.theta + q.phi).sin(),
+		q.theta.cos() + (q.theta + q.phi).cos()
+	]
+}
+
+fn canvas_xy(q: &DoublePendulum) -> [f32; 2] {
+	system_xy(q).map(|x| (x as f32 * (1.0 - MARGIN) - MIN) * WIDTH as f32 / (MAX - MIN))
+}
+
+fn main() {
+	let omega = 500.0;
+	let h = 1e-3;
+	let t = 20.0;
+
+	let mut state = Augmented::from(State {
+		q: DoublePendulum { theta: std::f64::consts::PI, phi: 0.1 },
+		p: DoublePendulum { theta: 0.0, phi: 0.0 },
+	}, omega);
+
+	let path = {
+		let mut pb = PathBuilder::new();
+
+		let [x, y] = canvas_xy(&state.average().q);
+		pb.move_to(x, y);
+
+		let n = (t / h) as u32;
+		for _ in 0..n {
+			state.evolve(h);
+			let [x, y] = canvas_xy(&state.average().q);
+			pb.line_to(x, y);
+		}
+
+		pb.finish().unwrap()
+	};
+
+	let mut paint = Paint::default();
+	paint.set_color_rgba8(0, 0, 0, 0xff);
+	paint.anti_alias = true;
+	let mut stroke = Stroke::default();
+	stroke.width = 4.0;
+	stroke.line_cap = LineCap::Round;
+	let mut pixmap = Pixmap::new(WIDTH, HEIGHT).unwrap();
+	pixmap.stroke_path(&path, &paint, &stroke, Transform::identity(), None);
+	pixmap.save_png("trace.png").unwrap();
+}