Math::Geometry: cleaned up Distance, removed use of Matrix.

The same functionality is now provided in Vector2::cross() which is
also more meaningful.

src/Math/Geometry/Distance.h

@@ -29,7 +29,6 @@
  */
 
 #include "Math/Functions.h"
-#include "Math/Matrix.h"
 #include "Math/Vector3.h"
 
 namespace Magnum { namespace Math { namespace Geometry {
@@ -46,14 +45,15 @@ class Distance {
          * @param point     Point
          *
          * The distance *d* is computed from point **p** and line defined by **a**
-         * and **b** using @ref Matrix::determinant() "determinant": @f[
-         *      d = \frac{|det(b - a a - point)|} {|b - a|}
+         * and **b** using @ref Vector2::cross() "perp-dot product": @f[
+         *      d = \frac{|(\boldsymbol b - \boldsymbol a)_\bot \cdot (\boldsymbol a - \boldsymbol p)|} {|\boldsymbol b - \boldsymbol a|}
          * @f]
          * Source: http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
          * @see linePointSquared(const Vector2&, const Vector2&, const Vector2&)
          */
         template<class T> inline static T linePoint(const Vector2<T>& a, const Vector2<T>& b, const Vector2<T>& point) {
-            return std::abs(Matrix<2, T>(b - a, a - point).determinant())/(b - a).length();
+            const Vector2<T> bMinusA = b - a;
+            return std::abs(Vector2<T>::cross(bMinusA, a - point))/bMinusA.length();
         }
 
         /**
@@ -67,8 +67,8 @@ class Distance {
          * compute the square root.
          */
         template<class T> inline static T linePointSquared(const Vector2<T>& a, const Vector2<T>& b, const Vector2<T>& point) {
-            Vector2<T> bMinusA = b - a;
-            return Math::pow<2>(Matrix<2, T>(bMinusA, a - point).determinant())/bMinusA.dot();
+            const Vector2<T> bMinusA = b - a;
+            return Math::pow<2>(Vector2<T>::cross(bMinusA, a - point))/bMinusA.dot();
         }
 
         /**
@@ -127,12 +127,12 @@ class Distance {
          * @see lineSegmentPointSquared()
          */
         template<class T> inline static T lineSegmentPoint(const Vector2<T>& a, const Vector2<T>& b, const Vector2<T>& point) {
-            Vector2<T> pointMinusA = point - a;
-            Vector2<T> pointMinusB = point - b;
-            Vector2<T> bMinusA = b - a;
-            T pointDistanceA = pointMinusA.dot();
-            T pointDistanceB = pointMinusB.dot();
-            T bDistanceA = bMinusA.dot();
+            const Vector2<T> pointMinusA = point - a;
+            const Vector2<T> pointMinusB = point - b;
+            const Vector2<T> bMinusA = b - a;
+            const T pointDistanceA = pointMinusA.dot();
+            const T pointDistanceB = pointMinusB.dot();
+            const T bDistanceA = bMinusA.dot();
 
             /* Point is before A */
             if(pointDistanceB > bDistanceA + pointDistanceA)
@@ -143,7 +143,7 @@ class Distance {
                 return std::sqrt(pointDistanceB);
 
             /* Between A and B */
-            return std::abs(Matrix<2, T>(bMinusA, -pointMinusA).determinant())/std::sqrt(bDistanceA);
+            return std::abs(Vector2<T>::cross(bMinusA, -pointMinusA))/std::sqrt(bDistanceA);
         }
 
         /**
@@ -153,12 +153,12 @@ class Distance {
          * other values, because it doesn't compute the square root.
          */
         template<class T> static T lineSegmentPointSquared(const Vector2<T>& a, const Vector2<T>& b, const Vector2<T>& point) {
-            Vector2<T> pointMinusA = point - a;
-            Vector2<T> pointMinusB = point - b;
-            Vector2<T> bMinusA = b - a;
-            T pointDistanceA = pointMinusA.dot();
-            T pointDistanceB = pointMinusB.dot();
-            T bDistanceA = bMinusA.dot();
+            const Vector2<T> pointMinusA = point - a;
+            const Vector2<T> pointMinusB = point - b;
+            const Vector2<T> bMinusA = b - a;
+            const T pointDistanceA = pointMinusA.dot();
+            const T pointDistanceB = pointMinusB.dot();
+            const T bDistanceA = bMinusA.dot();
 
             /* Point is before A */
             if(pointDistanceB > bDistanceA + pointDistanceA)
@@ -169,7 +169,7 @@ class Distance {
                 return pointDistanceB;
 
             /* Between A and B */
-            return Math::pow<2>(Matrix<2, T>(bMinusA, -pointMinusA).determinant())/bDistanceA;
+            return Math::pow<2>(Vector2<T>::cross(bMinusA, -pointMinusA))/bDistanceA;
         }
 
         /**
@@ -194,11 +194,11 @@ class Distance {
          * other values, because it doesn't compute the square root.
          */
         template<class T> static T lineSegmentPointSquared(const Vector3<T>& a, const Vector3<T>& b, const Vector3<T>& point) {
-            Vector3<T> pointMinusA = point - a;
-            Vector3<T> pointMinusB = point - b;
-            T pointDistanceA = pointMinusA.dot();
-            T pointDistanceB = pointMinusB.dot();
-            T bDistanceA = (b - a).dot();
+            const Vector3<T> pointMinusA = point - a;
+            const Vector3<T> pointMinusB = point - b;
+            const T pointDistanceA = pointMinusA.dot();
+            const T pointDistanceB = pointMinusB.dot();
+            const T bDistanceA = (b - a).dot();
 
             /* Point is before A */
             if(pointDistanceB > bDistanceA + pointDistanceA)