How to get these methods to work with multi-touch? - ios

Question

I found this code on a tutorial which pretty much sets a left or right side BOOL to YES if the touch started on a specific side of the screen and then checks when the touch moves to see if it changes sides on the screen in order to make the other BOOL yes.
So I am now trying to implement multi-touch but I am not sure how it would work with the following code? Does anyone have any idea how I would go upon it?
-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
touchStartPoint = [touch locationInView:self.view];
if (touchStartPoint.x < 160.0) {
touchLeftDown = TRUE;
}
else if (touchStartPoint.x > 160.0) {
touchRightDown = TRUE;
}
}
-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint currentTouchPoint = [touch locationInView:self.view];
if (touchStartPoint.x < 160.0 && currentTouchPoint.x < 160.0) {
touchLeftDown = TRUE;
}
else if (touchStartPoint.x > 160.0 && currentTouchPoint.x > 160.0)
{
touchRightDown = TRUE;
}
}
-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
touchLeftDown = touchRightDown = FALSE;
}
Thanks!
Edit1:
These are what the bools are doing in the game loop, pretty much what I am trying to achieve is that if there is a touch on both sides at the same time, the TOUCH_INCREMENT will be 0 since the touches on each side will cancel each other out. How would I achieve that? Anyway this is the code I am talking about:
if (touchLeftDown == TRUE) {
touchStep -= TOUCH_INCREMENT;
}
else if (touchRightDown == TRUE) {
touchStep += TOUCH_INCREMENT;
}
else {
touchStep = SLOWDOWN_FACTOR * touchStep;
}
touchStep = MIN(MAX(touchStep, -MAX_ABS_X_STEP), MAX_ABS_X_STEP);
pos.x += touchStep;

Answer 1

You can probably make this work without the touchStartPoint (i)var. The important thing is to not use -anyObject and instead to inspect each touch. The following code modifications might work for you:
-(void) countTouches:(NSSet *)touches withEvent:(UIEvent *)event{
int leftTouches=0;
int rightTouches=0;
for (UITouch *touch in touches)
{
CGPoint location = [touch locationInView:touch.view];
//just in case some code uses touchStartPoint
touchStartPoint=location;
if (location.x < 160.0) {
leftTouches++;
}
else if (location.x > 160.0) {
rightTouches++;
}
}
//reset touch state
touchLeftDown=FALSE;
//set touch state if touch found
if(leftTouches>0){
touchLeftDown=TRUE;
}
touchRightDown=FALSE;
if(rightTouches>0){
touchRightDown=TRUE;
}
}
-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
[self countTouches:touches withEvent:event];
}
-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
[self countTouches:touches withEvent:event];
}
-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
touchLeftDown = touchRightDown = FALSE;
}
Here I have created a function that is called by touchesBegan and touchesMoved because they need to implement the same logic. You may see some unintended side effects if touchStartPoint is being used in the code somehow.