T4 Add Spring Force using Hooke's Law

Find getSpringForce

Search [TODO 1] in ClothSim.cpp, you are expected to find the following:

// TODO: calculate spring force
glm::vec3 ClothSim::getSpringForce(int direction, int id) {

	// the rest spring length
	float lenRest = 0;
	if (direction == DIRS.NORTH || direction == DIRS.SOUTH) lenRest = restLengthZ;
	else if(direction == DIRS.WEST || direction == DIRS.EAST) lenRest = restLengthX;
	else lenRest = restLengthXZ;

	// the spring vector
	glm::vec3 vSpring = mesh->vertices[id].pos - mesh->vertices[getId(direction, id)].pos;
	// the spring length
	float lenSpring = glm::length(vSpring); // distance
	
	// the unit vector of spring direction
	glm::vec3 vSpringUnit = vSpring /lenSpring;

	// [TODO 1]: calculate spring force vector based on Hooke's law F = -k delta_x
	// 1.1 calculate the length change delta_len
	// replace 0 with your formula
	float delta_len = 0;

	// 1.2 Use Hooke's law F = -k * delta_len * vSpringUnit
	// k : spring_factor
	// replace glm::vec3(0.0) with your formula 
	glm::vec3 spring_force = glm::vec3(0.0);
	return spring_force;
}