From fcdf13efc8fa4def7ad930c003bc689ba001f788 Mon Sep 17 00:00:00 2001
From: Chris Loer <chris@felt.com>
Date: Thu, 9 Mar 2023 15:58:51 -0800
Subject: [PATCH] Add line intersection unit test.

---
 src/symbol/projection.test.ts | 26 +++++++++++++++++++++++++-
 src/symbol/projection.ts      |  2 +-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/symbol/projection.test.ts b/src/symbol/projection.test.ts
index ee92b4c68da..251356f1c62 100644
--- a/src/symbol/projection.test.ts
+++ b/src/symbol/projection.test.ts
@@ -1,4 +1,4 @@
-import {project} from './projection';
+import {findIntersectionPoint, project} from './projection';
 
 import Point from '@mapbox/point-geometry';
 import {mat4} from 'gl-matrix';
@@ -9,4 +9,28 @@ describe('Projection', () => {
         const matrix = mat4.create();
         expect(project(point, matrix).point.x).toBeCloseTo(point.x, 10);
     });
+
+    test('line intersection', () => {
+        const horizontal = [
+            new Point(0, 0),
+            new Point(10, 0)];
+        const vertical = [
+            new Point(30, -20),
+            new Point(30, -10)
+        ];
+        const intersection = findIntersectionPoint(horizontal[0], horizontal[1], vertical[0], vertical[1]);
+        expect(intersection).toEqual(new Point(30, 0));
+    });
+
+    test('parallel line intersection', () => {
+        const first = [
+            new Point(0, 0),
+            new Point(10, 0)];
+        const second = [
+            new Point(10, 0),
+            new Point(30, 0)
+        ];
+        const intersection = findIntersectionPoint(first[0], first[1], second[0], second[1]);
+        expect(intersection).toEqual(new Point(10, 0));
+    });
 });
diff --git a/src/symbol/projection.ts b/src/symbol/projection.ts
index e5dd87de4d9..99b9b3500ac 100644
--- a/src/symbol/projection.ts
+++ b/src/symbol/projection.ts
@@ -12,7 +12,7 @@ import type Transform from '../geo/transform';
 import type Painter from '../render/painter';
 import {WritingMode} from '../symbol/shaping';
 
-export {updateLineLabels, hideGlyphs, getLabelPlaneMatrix, getGlCoordMatrix, project, getPerspectiveRatio, placeFirstAndLastGlyph, placeGlyphAlongLine, xyTransformMat4};
+export {updateLineLabels, hideGlyphs, getLabelPlaneMatrix, getGlCoordMatrix, project, getPerspectiveRatio, placeFirstAndLastGlyph, placeGlyphAlongLine, xyTransformMat4, findIntersectionPoint};
 
 /*
  * # Overview of coordinate spaces