From 48dba6d57fd82e5213c2e9f4b99a549341cf6ed5 Mon Sep 17 00:00:00 2001
From: Joe Neeman <joe@neeman.me>
Date: Sun, 18 Jan 2026 12:47:33 -0600
Subject: [PATCH] Add an example to help visualize ops written in svg format

---
 examples/visualize_op.rs | 131 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 131 insertions(+)
 create mode 100644 examples/visualize_op.rs

diff --git a/examples/visualize_op.rs b/examples/visualize_op.rs
new file mode 100644
index 0000000..95eef07
--- /dev/null
+++ b/examples/visualize_op.rs
@@ -0,0 +1,131 @@
+use std::path::PathBuf;
+
+use anyhow::{anyhow, bail};
+use clap::Parser;
+use kurbo::BezPath;
+use svg::Document;
+
+use linesweeper::{
+    binary_op,
+    topology::{Contours, Topology},
+    BinaryOp, FillRule,
+};
+
+#[derive(Parser)]
+struct Cli {
+    #[arg(long)]
+    output: PathBuf,
+
+    #[arg(long)]
+    input: PathBuf,
+}
+
+pub fn main() -> anyhow::Result<()> {
+    let args = Cli::parse();
+    let input = std::fs::read_to_string(&args.input)?;
+    let mut input_lines = input.lines();
+    let op = input_lines.next().ok_or(anyhow!("no op line"))?;
+    let op = match op {
+        "union" => BinaryOp::Union,
+        "intersection" => BinaryOp::Intersection,
+        "difference" => BinaryOp::Difference,
+        "xor" => BinaryOp::Xor,
+        _ => bail!("unknown op {op}"),
+    };
+
+    let shape_a = input_lines.next().ok_or(anyhow!("no first shape"))?;
+    let shape_b = input_lines.next().ok_or(anyhow!("no second shape"))?;
+
+    for extra_line in input_lines {
+        if !extra_line.trim().is_empty() {
+            eprintln!("ignoring extra line: {extra_line}");
+        }
+    }
+
+    let shape_a = BezPath::from_svg(shape_a)?;
+    let shape_b = BezPath::from_svg(shape_b)?;
+
+    let eps = 1e-5;
+    let contours = binary_op(&shape_a, &shape_b, FillRule::EvenOdd, op)?;
+    let top = Topology::from_paths_binary(&shape_a, &shape_b, eps)?;
+    let bbox = top.bounding_box();
+    let min_x = bbox.min_x();
+    let min_y = bbox.min_y();
+    let max_x = bbox.max_x();
+    let max_y = bbox.max_y();
+    let pad = 1.0 + eps;
+    let one_width = max_x - min_x + 2.0 * pad;
+    let one_height = max_y - min_y + 2.0 * pad;
+    let stroke_width = (max_y - min_y).max(max_x - max_y) / 512.0;
+
+    let mut document = svg::Document::new().set(
+        "viewBox",
+        (min_x - pad, min_y - pad, one_width * 2.0, one_height),
+    );
+
+    // Draw the original document.
+    for (c, color) in [(&shape_a, "green"), (&shape_b, "blue")] {
+        let mut data = svg::node::element::path::Data::new();
+        for el in c {
+            let p = |point: kurbo::Point| (point.x, point.y);
+            data = match el {
+                kurbo::PathEl::MoveTo(p0) => data.move_to(p(p0)),
+                kurbo::PathEl::LineTo(p0) => data.line_to(p(p0)),
+                kurbo::PathEl::QuadTo(p0, p1) => data.quadratic_curve_to((p(p0), p(p1))),
+                kurbo::PathEl::CurveTo(p0, p1, p2) => data.cubic_curve_to((p(p0), p(p1), p(p2))),
+                kurbo::PathEl::ClosePath => data.close(),
+            };
+        }
+
+        let path = svg::node::element::Path::new()
+            .set("stroke", "black")
+            .set("stroke-width", stroke_width)
+            .set("stroke-linecap", "round")
+            .set("stroke-linejoin", "round")
+            .set("opacity", 0.5)
+            .set("fill", color)
+            .set("d", data);
+        document = document.add(path);
+    }
+
+    document = add_op(document, &contours, one_width, stroke_width);
+
+    svg::save(&args.output, &document)?;
+
+    Ok(())
+}
+
+fn add_op(mut doc: Document, contours: &Contours, x_off: f64, stroke_width: f64) -> Document {
+    for group in contours.grouped() {
+        let mut data = svg::node::element::path::Data::new();
+
+        for contour_idx in group {
+            let path = &contours[contour_idx].path;
+            for el in path.iter() {
+                data = match el {
+                    kurbo::PathEl::MoveTo(p) => data.move_to((p.x + x_off, p.y)),
+                    kurbo::PathEl::LineTo(p) => data.line_to((p.x + x_off, p.y)),
+                    kurbo::PathEl::QuadTo(p0, p1) => {
+                        data.quadratic_curve_to(((p0.x + x_off, p0.y), (p1.x + x_off, p1.y)))
+                    }
+                    kurbo::PathEl::CurveTo(p0, p1, p2) => data.cubic_curve_to((
+                        (p0.x + x_off, p0.y),
+                        (p1.x + x_off, p1.y),
+                        (p2.x + x_off, p2.y),
+                    )),
+                    kurbo::PathEl::ClosePath => data.close(),
+                };
+            }
+            data = data.close();
+        }
+        let path = svg::node::element::Path::new()
+            .set("d", data)
+            .set("stroke", "black")
+            .set("stroke-width", stroke_width)
+            .set("stroke-linecap", "round")
+            .set("stroke-linejoin", "round")
+            .set("fill", "pink");
+        doc = doc.add(path);
+    }
+    doc
+}