From 40bf82898f525971b43464b6f488f0e2450a10ff Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Mon, 6 May 2019 17:01:14 -0700
Subject: [PATCH] Fabric: Applying a transformation matrix to a point

Summary: The diff implements a function that applies given transformation to a point.

Reviewed By: JoshuaGross

Differential Revision: D15219263

fbshipit-source-id: 4cc0595b0dda38c1ede1f2885b800cbe57f54243
---
 ReactCommon/fabric/graphics/Transform.cpp | 26 +++++++++++++++++++++++
 ReactCommon/fabric/graphics/Transform.h   | 12 +++++++++++
 2 files changed, 38 insertions(+)

diff --git a/ReactCommon/fabric/graphics/Transform.cpp b/ReactCommon/fabric/graphics/Transform.cpp
index bfcb45f25..9848767b3 100644
--- a/ReactCommon/fabric/graphics/Transform.cpp
+++ b/ReactCommon/fabric/graphics/Transform.cpp
@@ -149,5 +149,31 @@ Transform Transform::operator*(Transform const &rhs) const {
   return result;
 }
 
+Float &Transform::at(int i, int j) {
+  return matrix[(i * 4) + j];
+}
+
+Float const &Transform::at(int i, int j) const {
+  return matrix[(i * 4) + j];
+}
+
+Point operator*(Point const &point, Transform const &transform) {
+  if (transform == Transform::Identity()) {
+    return point;
+  }
+
+  auto result = Point{};
+  result.x = transform.at(3, 0) + point.x * transform.at(0, 0) + point.y * transform.at(1, 0);
+  result.y = transform.at(3, 1) + point.x * transform.at(0, 1) + point.y * transform.at(1, 1);
+  auto w = transform.at(3, 3) + point.x * transform.at(0, 3) + point.y * transform.at(1, 3);
+
+  if (w != 1 && w != 0) {
+    result.x /= w;
+    result.y /= w;
+  }
+
+  return result;
+}
+
 } // namespace react
 } // namespace facebook
diff --git a/ReactCommon/fabric/graphics/Transform.h b/ReactCommon/fabric/graphics/Transform.h
index 75eff7559..71c9c6b58 100644
--- a/ReactCommon/fabric/graphics/Transform.h
+++ b/ReactCommon/fabric/graphics/Transform.h
@@ -9,6 +9,7 @@
 
 #include <folly/Hash.h>
 #include <react/graphics/Float.h>
+#include <react/graphics/Geometry.h>
 
 namespace facebook {
 namespace react {
@@ -59,12 +60,23 @@ struct Transform {
   bool operator==(Transform const &rhs) const;
   bool operator!=(Transform const &rhs) const;
 
+  /*
+   * Matrix subscript.
+   */
+  Float &at(int x, int y);
+  Float const &at(int x, int y) const;
+
   /*
    * Concatenates (multiplies) transform matrices.
    */
   Transform operator*(Transform const &rhs) const;
 };
 
+/*
+ * Applies tranformation to the given point.
+ */
+Point operator*(Point const &point, Transform const &transform);
+
 } // namespace react
 } // namespace facebook