From 8f3ee253772da5ff12cedf0bbc70da57ef7da002 Mon Sep 17 00:00:00 2001
From: numzero <numzer0@yandex.ru>
Date: Fri, 10 May 2024 16:06:26 +0300
Subject: [PATCH] Fast boundary finding

Unbounded cells start to cause trouble...
---
 src/bin/flat.rs | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/src/bin/flat.rs b/src/bin/flat.rs
index aad0287..687cced 100644
--- a/src/bin/flat.rs
+++ b/src/bin/flat.rs
@@ -119,13 +119,15 @@ fn draw_ray_2(gc: &mut Vec<Draw>, space: &impl Metric, grid: &Grid, base: Vec2,
 			gc.dash_length(6.0);
 			gc.new_path();
 			gc.move_to(p.x, p.y);
-			let mut ray = cell.ray_to_local(Ray { pos: p, dir: v });
-			while cell.is_inside(ray.pos) && !ray.pos.abs().cmpgt(Vec2::splat(1000.0)).any() {
-				ray = Ray { pos: ray.pos + ray.dir * dt, dir: ray.dir };
-				p = cell.pos_to_global(ray.pos);
-				gc.line_to(p.x, p.y);
+			let ray = cell.ray_to_local(Ray { pos: p, dir: v });
+			if let Some(ray) = cell.to_boundary(ray) {
+				Ray { pos: p, dir: v } = cell.ray_to_global(ray);
+			} else {
+				gc.stroke();
+				gc.new_dash_pattern();
+				return;
 			}
-			Ray { pos: p, dir: v } = cell.ray_to_global(ray);
+			gc.line_to(p.x, p.y);
 			gc.stroke();
 			gc.new_dash_pattern();
 			gc.new_path();
@@ -244,6 +246,30 @@ trait FlatCell: std::fmt::Debug {
 		pos.cmpge(bnd.0).all() && pos.cmple(bnd.1).all()
 	}
 	fn local_bounds(&self) -> (Vec2, Vec2);
+
+	fn to_boundary(&self, ray: Ray) -> Option<Ray> {
+		assert!(self.is_inside(ray.pos));
+		let sgn = ray.dir.signum();
+		let p = ray.pos * sgn;
+		let v = ray.dir * sgn;
+		let mut bnd = self.local_bounds();
+		if sgn.x < 0.0 {
+			(bnd.0.x, bnd.1.x) = (-bnd.1.x, -bnd.0.x);
+		}
+		if sgn.y < 0.0 {
+			(bnd.0.y, bnd.1.y) = (-bnd.1.y, -bnd.0.y);
+		}
+		let t = if (bnd.1.x - p.x) * v.y <= (bnd.1.y - p.y) * v.x {
+			(bnd.1.x - p.x) / v.x
+		} else {
+			(bnd.1.y - p.y) / v.y
+		};
+		if t <= 1000.0 {
+			Some(Ray { pos: sgn * (p + v * t), dir: sgn * v })
+		} else {
+			None
+		}
+	}
 }
 
 #[derive(Debug)]