From 4d4dc91ff46e57c72b89a30b9ba5d86a26efee21 Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sun, 10 Aug 2014 16:57:34 -0700
Subject: [PATCH] Add Matrix4 Inverse and Transpose

Transpose is easy, with a bool flag to determine whether to access elements in row-major or column-major format. Inverse is more difficult, so this change only does translation inverses.
---
 src/basics/matrix.cc | 69 +++++++++++++++++++++++++++++++++++++++++---
 src/basics/matrix.hh | 16 ++++++++++
 test/test_basics.cc  | 18 ++++++++++++
 3 files changed, 99 insertions(+), 4 deletions(-)

diff --git a/src/basics/matrix.cc b/src/basics/matrix.cc
index 6c24450..5779794 100644
--- a/src/basics/matrix.cc
+++ b/src/basics/matrix.cc
@@ -65,7 +65,8 @@ Matrix4::Translation(Double x,
  * charles::basics::Matrix4::Matrix4 --
  */
 Matrix4::Matrix4()
-    : mData()
+    : mData(),
+      mTransposed(false)
 { }
 
 
@@ -73,6 +74,7 @@ Matrix4::Matrix4()
  * charles::basics::Matrix4::Matrix4 --
  */
 Matrix4::Matrix4(const Double data[16])
+    : mTransposed(false)
 {
     memcpy(mData, data, sizeof(Double) * 16);
 }
@@ -83,7 +85,13 @@ Matrix4::Matrix4(const Double data[16])
  */
 Matrix4::Matrix4(const Matrix4 &rhs)
     : Matrix4(rhs.mData)
-{ }
+{
+    /*
+     * Needs to be in the body instead of the initializer list because
+     * (apparently) delegating constructors must be the only thing in the list.
+     */
+    mTransposed = rhs.mTransposed;
+}
 
 
 /*
@@ -93,6 +101,7 @@ Matrix4&
 Matrix4::operator=(const Matrix4 &rhs)
 {
     memcpy(mData, rhs.mData, sizeof(Double) * 16);
+    mTransposed = rhs.mTransposed;
     return *this;
 }
 
@@ -138,7 +147,12 @@ Matrix4::operator()(UInt i,
         ss << "matrix index out of bounds: i = " << i << ", j = " << j;
         throw std::out_of_range(ss.str());
     }
-    return mData[i*4 + j];
+
+    if (!mTransposed) {
+        return mData[i*4 + j];
+    } else {
+        return mData[i + j*4];
+    }
 }
 
 
@@ -155,7 +169,11 @@ Matrix4::operator()(UInt i,
         ss << "matrix index out of bounds: i = " << i << ", j = " << j;
         throw std::out_of_range(ss.str());
     }
-    return mData[i*4 + j];
+    if (!mTransposed) {
+        return mData[i*4 + j];
+    } else {
+        return mData[i + j*4];
+    }
 }
 
 
@@ -255,6 +273,28 @@ Matrix4::operator*(const Vector4 &rhs)
 }
 
 
+/*
+ * charles::basics::Matrix4::Transpose --
+ */
+Matrix4&
+Matrix4::Transpose()
+{
+    mTransposed = !mTransposed;
+    return *this;
+}
+
+
+Matrix4&
+Matrix4::Inverse()
+{
+    /* XXX: Only translation matrices are supported right now. */
+    operator()(0,3) = -operator()(0,3);
+    operator()(1,3) = -operator()(1,3);
+    operator()(2,3) = -operator()(2,3);
+    return *this;
+}
+
+
 /*
  * charles::basics::operator* --
  */
@@ -266,6 +306,27 @@ operator*(Double lhs,
     return rhs * lhs;
 }
 
+
+/*
+ * charles::basics::Transposed --
+ */
+Matrix4
+Transposed(Matrix4 m)
+{
+    return m.Transpose();
+}
+
+
+/*
+ * charles::basics::Inverse --
+ */
+Matrix4
+Inverse(Matrix4 m)
+{
+    return m.Inverse();
+}
+
+
 } /* namespace mespace  */
 } /* namespace charles */
 
diff --git a/src/basics/matrix.hh b/src/basics/matrix.hh
index 2128e45..ba8309c 100644
--- a/src/basics/matrix.hh
+++ b/src/basics/matrix.hh
@@ -73,15 +73,31 @@ struct Matrix4
     Vector4 operator*(const Vector4 &rhs) const;
     /** @} */
 
+    Matrix4& Transpose();
+    Matrix4& Inverse();
+
 protected:
     /** The matrix data */
     Double mData[16];
+
+    /**
+     * `true` if the matrix has been transposed (i.e. should be indexed in
+     * column-major format).
+     */
+    bool mTransposed;
 };
 
 
 /** Scalar multiplication, scalar factor on the left. */
 Matrix4 operator*(Double lhs, const Matrix4 &rhs);
 
+
+/** Transpose the given matrix. */
+Matrix4 Transposed(Matrix4 rhs);
+
+/** Invert the given matrix. */
+Matrix4 Inverse(Matrix4 rhs);
+
 } /* namespace basics */
 } /* namespace charles */
 
diff --git a/test/test_basics.cc b/test/test_basics.cc
index dad6dae..a5b99bb 100644
--- a/test/test_basics.cc
+++ b/test/test_basics.cc
@@ -293,3 +293,21 @@ TEST_F(Matrix4Test, IdentityVectorMultiplication)
     EXPECT_EQ(p1.Y(), v1.Y());
     EXPECT_EQ(p1.Z(), v1.Z());
 }
+
+
+TEST_F(Matrix4Test, Transpose)
+{
+    Matrix4 t1 = Transposed(m1);
+    for (UInt i = 0; i < 4; i++) {
+        for (UInt j = 0; j < 4; j++) {
+            EXPECT_EQ(m1(i,j), t1(j,i));
+        }
+    }
+
+    t1.Transpose();
+    for (UInt i = 0; i < 4; i++) {
+        for (UInt j = 0; j < 4; j++) {
+            EXPECT_EQ(m1(i,j), t1(i,j));
+        }
+    }
+}