Cocos2d rotation on touches moved problem

Question

I have a spear like sprite. It rotation is decided by touchesMoved method. whenever the user slides his finger it points towards that touch. This is my method:

- (void)ccTouchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch* touch = [touches anyObject];
    CGPoint location = [touch locationInView: [touch view]];


    float angleRadians = atanf((float)location.y / (float)location.x);
    float angleDegrees = CC_RADIANS_TO_DEGREES(angleRadians);

    spear.rotation = -1 * angleDegrees;

}

This kinda works, but only from 0 to 45 degrees. and it goes opposite. So as I am moving from finger for bottom to top, it rotates clockwise (it should follow direction of fnger and rotate counter clockwise). From 45 to 90, it works fine (moves counter clickwise) but only if i start the touch in upper diagonal of the screen.

What am i doing wrong? Thanks

Answer 1

#define PTM_RATIO 32

- (void)ccTouchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

    for( UITouch *touch in touches ) {

        CGPoint location = [touch locationInView: [touch view]];

        location = [[CCDirector sharedDirector] convertToGL: location];

        b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);

        spriteBody->SetTransform(locationWorld,spriteBody->GetAngle());
    }
}

-(void) tick: (ccTime) dt
{

    //It is recommended that a fixed time step is used with Box2D for stability
    //of the simulation, however, we are using a variable time step here.
    //You need to make an informed choice, the following URL is useful
    //http://gafferongames.com/game-physics/fix-your-timestep/

    int32 velocityIterations = 8;
    int32 positionIterations = 1;

    // Instruct the world to perform a single step of simulation. It is
    // generally best to keep the time step and iterations fixed.
    m_world->Step(dt, velocityIterations, positionIterations);

    //  for (int i = 0; i < (int)birds.size(); i++)
    //      birds[i]->render();

    //Iterate over the bodies in the physics world
    for (b2Body* b = m_world->GetBodyList(); b; b = b->GetNext())
    {
        if (b->GetUserData() != NULL) {
            //Synchronize the AtlasSprites position and rotation with the corresponding body
            CCSprite *myActor = (CCSprite*)b->GetUserData();
            myActor.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
            myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
        }   
    }
}

Answer 2

Figured out what was wrong. I needed to change the CGPoint I got from the touches into GL point like this:

CGPoint location = [touch locationInView: [touch view]];

location = [[CCDirector sharedDirector] convertToGL: location];

Silly me. Should have thought about this before.

Answer 3

CGPoint touchLocation = [touch locationInView: [touch view]];
touchLocation = [[CCDirector sharedDirector] convertToGL:touchLocation];
touchLocation = [self convertToNodeSpace:touchLocation];    
GPoint diff = ccpSub(touchLocation, _player.position);

//rotate to face the touch
CGPoint diff = ccpSub(_player.position, touchLocation);
float angleRadians = atanf((float)diff.y / (float)diff.x);
float angleDegrees = CC_RADIANS_TO_DEGREES(angleRadians);
float cocosAngle = -1 * angleDegrees;

if(diff.x < 0)
{
            cocosAngle += 180;
}

id actionRotateTo = [CCRotateTo actionWithDuration:0.1 angle:cocosAngle];
[_player runAction:actionRotateTo];