From 474ee631b25b8a032e59520a4bc3f096c8789b1f Mon Sep 17 00:00:00 2001
From: Noel Berry <thenberry@gmail.com>
Date: Sun, 11 Oct 2020 13:50:44 -0700
Subject: [PATCH] angle utility methods

---
 public/blah/math/calc.cpp |  6 ++++++
 public/blah/math/calc.h   |  2 ++
 public/blah/math/vec2.cpp | 11 +++++++++++
 public/blah/math/vec2.h   |  2 ++
 4 files changed, 21 insertions(+)

diff --git a/public/blah/math/calc.cpp b/public/blah/math/calc.cpp
index 1df36af..3bc2f9b 100644
--- a/public/blah/math/calc.cpp
+++ b/public/blah/math/calc.cpp
@@ -119,6 +119,12 @@ float Calc::angle_diff(float radians_a, float radians_b)
 	return mod((radians_b - radians_a) + PI, TAU) - PI;
 }
 
+float Calc::angle_lerp(float radians_a, float radians_b, float p)
+{
+	const auto shortest_angle = mod(mod(radians_b - radians_a, TAU) + (TAU + PI), TAU) - PI;
+	return radians_a + mod(shortest_angle * p, TAU);
+}
+
 float Calc::lerp(float a, float b, float t)
 {
 	return a + (b - a) * t;
diff --git a/public/blah/math/calc.h b/public/blah/math/calc.h
index 6a77e35..732ac7e 100644
--- a/public/blah/math/calc.h
+++ b/public/blah/math/calc.h
@@ -61,6 +61,8 @@ namespace Blah
 		float snap(float val, float interval);
 
 		float angle_diff(float radians_a, float radians_b);
+		
+		float angle_lerp(float radians_a, float radians_b, float p);
 
 		float lerp(float a, float b, float t);
 
diff --git a/public/blah/math/vec2.cpp b/public/blah/math/vec2.cpp
index 14718f0..4518fad 100644
--- a/public/blah/math/vec2.cpp
+++ b/public/blah/math/vec2.cpp
@@ -35,6 +35,17 @@ Vec2 Vec2::normal() const
 	float length = this->length();
 	return Vec2(x / length, y / length);
 }
+
+Vec2 Vec2::turn_right() const
+{
+	return Vec2(y, -x);
+}
+
+Vec2 Vec2::turn_left() const
+{
+	return Vec2(-y, x);
+}
+
 float Vec2::length() const { return sqrtf(x * x + y * y); }
 float Vec2::length_squared() const { return x * x + y * y; }
 
diff --git a/public/blah/math/vec2.h b/public/blah/math/vec2.h
index e505bbf..8f4c51a 100644
--- a/public/blah/math/vec2.h
+++ b/public/blah/math/vec2.h
@@ -35,6 +35,8 @@ namespace Blah
 		bool operator !=(const Vec2& rhs);
 		
 		Vec2 normal() const;
+		Vec2 turn_right() const;
+		Vec2 turn_left() const;
 		float length() const;
 		float length_squared() const;
 		Vec2 perpendicular() const;