More vec3 operations

include/utility.hpp

@@ -26,10 +26,16 @@ unsigned ij2index(unsigned i, unsigned j, unsigned Ny);
 
 std::array<float, 3> operator+=(std::array<float, 3>&, const std::array<float, 3>&);
 
+std::array<float, 3> operator-(std::array<float, 3>, const std::array<float, 3>&);
+
 std::array<float, 3> cross(const std::array<float, 3>&, const std::array<float, 3>&);
 
 std::array<float, 3> operator/=(std::array<float, 3>&, const float);
 
+float length(const std::array<float, 3>&);
+
+std::array<float, 3> normal(const std::array<float, 3>&, const std::array<float, 3>&, const std::array<float, 3>&);
+
 glm::mat4 scale_z(float z0, float factor);
 
 

src/utility.cpp

@@ -45,6 +45,13 @@ std::array<float, 3> operator+=(std::array<float, 3>& lhs, const std::array<floa
   return lhs;
 }
 
+std::array<float, 3> operator-(std::array<float, 3> lhs, const std::array<float, 3>& rhs) {
+	lhs[0] -= rhs[0];
+	lhs[1] -= rhs[1];
+	lhs[2] -= rhs[2];
+	return lhs;
+}
+
 std::array<float, 3> cross(const std::array<float, 3>& v, const std::array<float, 3>& w){
   std::array<float, 3> cp;
   cp[0] = v[1]*w[2] - v[2]*w[1];
@@ -62,6 +69,18 @@ std::array<float, 3> operator/=(std::array<float, 3>& v, const float d){
   return v;
 }
 
+float length(const std::array<float, 3>& v) {
+	return std::sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
+}
+
+std::array<float, 3> normal(const std::array<float, 3>& p1, const std::array<float, 3>& p2, const std::array<float, 3>& p3) {
+	std::array<float, 3> v1 = p2 - p1;
+	std::array<float, 3> v2 = p3 - p1;
+	std::array<float, 3> crs = cross(v1, v2);
+	crs /= length(crs);
+	return crs;
+}
+
 glm::mat4 scale_z(float z0, float factor){
   glm::mat4 transf (1.f);
   transf = glm::translate(glm::scale(glm::translate(transf, glm::vec3(0.f,0.f,-z0)), glm::vec3(1.,1.,factor)), glm::vec3(0.,0.,z0));