From 2be1ff3763eb044b609edafb83d6392b1c4cd204 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20Vondru=C5=A1?= <mosra@centrum.cz>
Date: Fri, 27 Apr 2012 02:29:09 +0200
Subject: [PATCH] Added Vector::lengthSquared() function.

The name is a little bit misleading, but it is for more efficient vector
length comparisons.
---
 src/Math/Test/VectorTest.cpp |  4 ++++
 src/Math/Test/VectorTest.h   |  1 +
 src/Math/Vector.h            | 18 +++++++++++++++++-
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/Math/Test/VectorTest.cpp b/src/Math/Test/VectorTest.cpp
index 38f13c919..0726925ea 100644
--- a/src/Math/Test/VectorTest.cpp
+++ b/src/Math/Test/VectorTest.cpp
@@ -93,6 +93,10 @@ void VectorTest::length() {
     QCOMPARE(Vector4(1.0f, 2.0f, 3.0f, 4.0f).length(), 5.4772256f);
 }
 
+void VectorTest::lengthSquared() {
+    QCOMPARE(Vector4(1.0f, 2.0f, 3.0f, 4.0f).lengthSquared(), 30.0f);
+}
+
 void VectorTest::normalized() {
     QVERIFY(Vector4(1.0f, 1.0f, 1.0f, 1.0f).normalized() == Vector4(0.5f, 0.5f, 0.5f, 0.5f));
 }
diff --git a/src/Math/Test/VectorTest.h b/src/Math/Test/VectorTest.h
index 70c7222e3..143ea01a3 100644
--- a/src/Math/Test/VectorTest.h
+++ b/src/Math/Test/VectorTest.h
@@ -30,6 +30,7 @@ class VectorTest: public QObject {
         void multiplyDivide();
         void addSubstract();
         void length();
+        void lengthSquared();
         void normalized();
         void product();
         void angle();
diff --git a/src/Math/Vector.h b/src/Math/Vector.h
index 66a88f8f7..11fa9da49 100644
--- a/src/Math/Vector.h
+++ b/src/Math/Vector.h
@@ -218,11 +218,27 @@ template<class T, size_t size> class Vector {
             return out;
         }
 
-        /** @brief %Vector length */
+        /**
+         * @brief %Vector length
+         *
+         * @see lengthSquared()
+         */
         inline T length() const {
             return sqrt(dot(*this, *this));
         }
 
+        /**
+         * @brief %Vector length squared
+         *
+         * More efficient than length() for comparing vector length with
+         * other values, because it doesn't compute the square root, just the
+         * dot product: @f$ a \cdot a < length \cdot length @f$ is faster
+         * than @f$ \sqrt{a \cdot a} < length @f$.
+         */
+        inline T lengthSquared() const {
+            return dot(*this, *this);
+        }
+
         /** @brief Normalized vector (of length 1) */
         inline Vector<T, size> normalized() const {
             return *this/length();