SAT.cpp

// checks for collisions using the separating axis theorem 
bool VWCar::isColliding(VWCollisionObject* colObj){
	int i;
	// define the axes: 2 from collision object 2 from car
	vector<ofxVec2f*> axes;
	axes.reserve(4);
	
	vector<ofxVec2f*>* objCorners = colObj->getCorners();
	
	if(objCorners->empty()){
		return false;
	}
	
	for(i = 0; i < 4; i++){
		ofxVec2f* axis = new ofxVec2f();
		axes.push_back(axis);
	}
	
	// cornersAbs is a vector that holds the coordinates for the corners of the car that is colliding 
	axes[0]->set(cornersAbs[0]->x - cornersAbs[1]->x, cornersAbs[0]->y - cornersAbs[1]->y);
	axes[1]->set(cornersAbs[0]->x - cornersAbs[3]->x, cornersAbs[0]->y - cornersAbs[3]->y);
	axes[2]->set(objCorners->at(0)->x - objCorners->at(1)->x, objCorners->at(0)->y - objCorners->at(1)->y);
	axes[3]->set(objCorners->at(0)->x - objCorners->at(3)->x, objCorners->at(0)->y - objCorners->at(3)->y);
	
	// perpendicular actually finds the normalized vector perpendicular to the one it operates on
	// for the sake of this algorithm it doesn't actually need to be normalized
	for(i = 0; i < 4; i++){
		axes[i]->perpendicular();
	}
	
	float minCar;
	float maxCar;
	float minObj;
	float maxObj;
	
	float scalarCar;
	float scalarObj;
	
	// for each axis project the objects onto the axis
	for(i = 0; i < 4; i++){
	
		// for each corner of the object dot it with the axis
		for (int j = 0; j < 4; j++) {
			scalarCar = ((cornersAbs[j]->x * axes[i]->x) + (cornersAbs[j]->y * axes[i]->y));
			scalarObj = ((objCorners->at(j)->x * axes[i]->x) + (objCorners->at(j)->y * axes[i]->y));
			
			if(j == 0){
				minCar = scalarCar;
				maxCar = scalarCar;
				minObj = scalarObj;
				maxObj = scalarObj;
			}
			
			// record the min and max for each object
			
			if(scalarCar < minCar){
				minCar = scalarCar;
			}
			
			if(scalarCar > maxCar){
				maxCar = scalarCar;
			}
			
			if(scalarObj < minObj){
				minObj = scalarObj;
			}
			
			if(scalarObj > maxObj){
				maxObj = scalarObj;
			}
		}
		
		// if they don't overlap then they aren't colliding
		if(minObj > maxCar || maxObj < minCar || minCar > maxObj || maxCar < minObj){
			
			// clean up
			while(!axes.empty()){
				ofxVec2f* temp = axes.at(axes.size()-1);
				axes.pop_back();
				delete temp;
			}
			
			return false;
		}
	}
		
	// clean up
	while(!axes.empty()){
		ofxVec2f* temp = axes.at(axes.size()-1);
		axes.pop_back();
		delete temp;
	}
	
	return true;
}