New collision detection

sdlpp/sdlpp_geometry_line.hpp

@@ -5,10 +5,12 @@
 #include "sdlpp_vector.hpp"
 #include "sdlpp_line.hpp"
 #include <algorithm>
+#include <iostream>
 
 namespace SDLPP {
-template<typename T>
-Vec2D<T> pointProjectionOnLine( const Vec2D<T> &point, const Line<T> &line ) {
+template < typename T >
+Vec2D< T > pointProjectionOnLine( const Vec2D< T > &point,
+                                  const Line< T > &line ) {
     /* from here -
      * https://stackoverflow.com/questions/849211/shortest-distance-between-a-point-and-a-line-segment
      */
@@ -21,10 +23,49 @@ Vec2D<T> pointProjectionOnLine( const Vec2D<T> &point, const Line<T> &line ) {
                                           length_squared ) );
     return line.getStart() + t * ( line.getEnd() - line.getStart() );
 }
-template<typename T>
-double pointLineDistance( const Vec2D<T> &point, const Line<T> &line ) {
+template < typename T >
+double pointLineDistance( const Vec2D< T > &point, const Line< T > &line ) {
     return vecDistance( point, pointProjectionOnLine( point, line ) );
 }
+template < typename T >
+int _determinant( const Line< T > &line, const Vec2D< T > &point ) {
+    auto res = ( line.getEnd().getX() - line.getStart().getX() ) *
+                   ( point.getY() - line.getStart().getY() ) -
+               ( line.getEnd().getY() - line.getStart().getY() ) *
+                   ( point.getX() - line.getStart().getX() );
+    if ( res < 0 )
+        return -1;
+    if ( res > 0 )
+        return 1;
+    return 0;
+}
+template < typename T >
+bool linesCross( const Line< T > &a, const Line< T > &b ) {
+    auto det_a_s = _determinant( a, b.getStart() );
+    auto det_a_e = _determinant( a, b.getEnd() );
+    if ( det_a_s == det_a_e && det_a_s != 0 )
+        return false;
+
+    // det_a_s == det_a_e == 0, means that lines have the same vector,
+    // we need to find out if they overlap
+    if ( det_a_s == det_a_e ) {
+        if ( a.getStart().getX() == a.getEnd().getX() ) {
+            // vertical lines
+            return a.bottomost().getY() > b.topmost().getY() &&
+                   a.topmost().getY() < b.bottomost().getY();
+        } else {
+            // horizontal lines
+            return a.leftmost().getX() < b.rightmost().getX() &&
+                   a.rightmost().getX() > b.leftmost().getX();
+        }
+    }
+
+    auto det_b_s = _determinant( b, a.getStart() );
+    auto det_b_e = _determinant( b, a.getEnd() );
+    if ( det_b_s == det_b_e )
+        return false;
+    return true;
+}
 } // namespace SDLPP
 
 #endif