From a77accf3f4d70174f4b213abcd1847d0fc705094 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Wed, 26 Apr 2023 16:53:06 +0200
Subject: [PATCH] LibGfx: Add AffineTransform::rotation()

Extracts the rotation from a 2D matrix.
---
 Userland/Libraries/LibGfx/AffineTransform.cpp | 11 +++++++++++
 Userland/Libraries/LibGfx/AffineTransform.h   |  1 +
 2 files changed, 12 insertions(+)

diff --git a/Userland/Libraries/LibGfx/AffineTransform.cpp b/Userland/Libraries/LibGfx/AffineTransform.cpp
index 4e4fbaef4b..31da63b65b 100644
--- a/Userland/Libraries/LibGfx/AffineTransform.cpp
+++ b/Userland/Libraries/LibGfx/AffineTransform.cpp
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Math.h>
 #include <AK/Optional.h>
 #include <LibGfx/AffineTransform.h>
 #include <LibGfx/Quad.h>
@@ -229,4 +230,14 @@ Quad<float> AffineTransform::map_to_quad(Rect<float> const& rect) const
     };
 }
 
+float AffineTransform::rotation() const
+{
+    auto rotation = AK::atan2(b(), a());
+    while (rotation < -AK::Pi<float>)
+        rotation += 2.0f * AK::Pi<float>;
+    while (rotation > AK::Pi<float>)
+        rotation -= 2.0f * AK::Pi<float>;
+    return rotation;
+}
+
 }
diff --git a/Userland/Libraries/LibGfx/AffineTransform.h b/Userland/Libraries/LibGfx/AffineTransform.h
index 45555eec21..beebcdc855 100644
--- a/Userland/Libraries/LibGfx/AffineTransform.h
+++ b/Userland/Libraries/LibGfx/AffineTransform.h
@@ -54,6 +54,7 @@ public:
     [[nodiscard]] float x_translation() const;
     [[nodiscard]] float y_translation() const;
     [[nodiscard]] FloatPoint translation() const;
+    [[nodiscard]] float rotation() const;
 
     AffineTransform& scale(float sx, float sy);
     AffineTransform& scale(FloatPoint s);