How to rotate a CGVector by a right angle? - ios

Question

I want to store direction of my sprite as CGVector,
I have only 4 possible vectors:
CGVector up = CGVectorMake(0, 100);
CGVector down = CGVectorMake(0, -100);
CGVector left = CGVectorMake(-100, 0);
CGVector right = CGVectorMake(100, 0);
and I have 2 events:
-(void) turnLeft;
-(void) turnRight;
in case that now (my_sprite.direction == CGVector(0,100)) and event turnRight happened how can I get CGVector(100, 0)???
P.S. I don't want to many if or switch statements, because in the future should be much more vectors.

Answer 1

Since you want the ability to use more directions in the future, It would be better to just store angle and speed.
- (void)applyDirectionChange{
CGFloat x = sinf(self.angle)*self.speed;
CGFloat y = cosf(self.angle)*self.speed;
self.direction = CGVectorMake(x,y);
}
- (void)turnRight{
self.angle += 90*M_PI/180;
[self applyDirectionChange];
}
- (void)turnLeft{
self.angle -= 90*M_PI/180;
[self applyDirectionChange];
}
if you still want to keep your constant vectors, put them in an array in the right order and have an current direction index pointing to the right vector:
//declarations
NSUInteger currentDirectionIndex;
NSUInteger numDirections;
CGVector[4] directions;
//initialize them somewhere
currentDirectionIndex = 0;
numDirections = 4;
directions[0] = up;
directions[1] = right;
directions[2] = down;
directions[3] = left;
//in your methods
- (void)turnRight{
currentDirectionIndex++;
if(currentDirectionIndex>=numDirections)
currentDirectionIndex = 0;
self.direction = directions[currentDirectionIndex];
}
- (void)turnLeft{
currentDirectionIndex--;
if(currentDirectionIndex<0)
currentDirectionIndex = numDirections-1;
self.direction = directions[currentDirectionIndex];
}

Answer 2

Let's rearrange your vectors into this order:
CGVector up = CGVectorMake( 0, 100);
CGVector right = CGVectorMake( 100, 0);
CGVector down = CGVectorMake( 0, -100);
CGVector left = CGVectorMake(-100, 0);
Now we can see that rotating a vector 90 degrees clockwise is the same as swapping the coordinates and then negating the Y coordinate:
CGVector vectorByRotatingVectorClockwise(CGVector in) {
CGVector out;
out.dx = in.dy;
out.dy = -in.dx;
return out;
}