From dc22e59a1a9c59a2add31af993fb53ac5fa84088 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Fri, 26 Jun 2020 18:23:38 +0200
Subject: [PATCH] LibGfx: Teach AffineTransform how to rotate and multiply

---
 Libraries/LibGfx/AffineTransform.cpp | 22 ++++++++++++++++++++++
 Libraries/LibGfx/AffineTransform.h   |  7 +++++++
 2 files changed, 29 insertions(+)

diff --git a/Libraries/LibGfx/AffineTransform.cpp b/Libraries/LibGfx/AffineTransform.cpp
index 02dad6c24e..77738c25ed 100644
--- a/Libraries/LibGfx/AffineTransform.cpp
+++ b/Libraries/LibGfx/AffineTransform.cpp
@@ -69,6 +69,28 @@ AffineTransform& AffineTransform::translate(float tx, float ty)
     return *this;
 }
 
+AffineTransform& AffineTransform::multiply(const AffineTransform& other)
+{
+    AffineTransform result;
+    result.m_values[0] = other.a() * a() + other.b() * c();
+    result.m_values[1] = other.a() * b() + other.b() * d();
+    result.m_values[2] = other.c() * a() + other.d() * c();
+    result.m_values[3] = other.c() * b() + other.d() * d();
+    result.m_values[4] = other.e() * a() + other.f() * c() + e();
+    result.m_values[5] = other.e() * b() + other.f() * d() + f();
+    *this = result;
+    return *this;
+}
+
+AffineTransform& AffineTransform::rotate_radians(float radians)
+{
+    float sin_angle = sinf(radians);
+    float cos_angle = cosf(radians);
+    AffineTransform rotation(cos_angle, sin_angle, -sin_angle, cos_angle, 0, 0);
+    multiply(rotation);
+    return *this;
+}
+
 void AffineTransform::map(float unmapped_x, float unmapped_y, float& mapped_x, float& mapped_y) const
 {
     mapped_x = (m_values[0] * unmapped_x + m_values[2] * unmapped_y + m_values[4]);
diff --git a/Libraries/LibGfx/AffineTransform.h b/Libraries/LibGfx/AffineTransform.h
index 9e6aa35113..0a3613171d 100644
--- a/Libraries/LibGfx/AffineTransform.h
+++ b/Libraries/LibGfx/AffineTransform.h
@@ -39,6 +39,11 @@ public:
     {
     }
 
+    AffineTransform(float a, float b, float c, float d, float e, float f)
+        : m_values { a, b, c, d, e, f }
+    {
+    }
+
     bool is_identity() const;
 
     void map(float unmapped_x, float unmapped_y, float& mapped_x, float& mapped_y) const;
@@ -64,6 +69,8 @@ public:
 
     AffineTransform& scale(float sx, float sy);
     AffineTransform& translate(float tx, float ty);
+    AffineTransform& rotate_radians(float);
+    AffineTransform& multiply(const AffineTransform&);
 
 private:
     float m_values[6] { 0 };