From 24afb2a24f97c412fc29b6ff6f67fa741f99aa49 Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Thu, 12 Jan 2023 14:43:52 -0800
Subject: [PATCH] Fix angle_between

---
 manimlib/shaders/quadratic_bezier_stroke/geom.glsl | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/manimlib/shaders/quadratic_bezier_stroke/geom.glsl b/manimlib/shaders/quadratic_bezier_stroke/geom.glsl
index 1814a6ac..0d54d9a9 100644
--- a/manimlib/shaders/quadratic_bezier_stroke/geom.glsl
+++ b/manimlib/shaders/quadratic_bezier_stroke/geom.glsl
@@ -52,9 +52,16 @@ const float ANGLE_THRESHOLD = 1e-3;
 #INSERT rotate.glsl
 
 
+float atan2(float y, float x){
+    // Normally atan is undefined for x = 0
+    if(x == 0) return sign(y) * 0.5 * PI;
+    return atan(y, x);
+}
+
+
 float angle_between(vec2 v1, vec2 v2){
     vec2 quot = complex_div(v2, v1);  // Defined in get_xy_to_uv
-    return sign(quot.x) * atan(quot.y, quot.x);
+    return atan2(quot.y, quot.x);
 }