I am using Box2d and Cocos2d to develop an iPhone game. I have a ball in the center of the screen with a simple boundary created using fixtures etc. What I want to do is add the functionality so that a user can "swipe" the ball to apply force and basically flick it across the screen.
I am using the following code to achieve this:
b2Vec2 force = b2Vec2(30, 30);
_body->ApplyLinearImpulse(force, _ballBodyDef->position);
If I apply a linear impulse during the init function the ball fires off in the correct direction and behaves as it should do. It doesnt do anything, however, if I put it into the handlePan function that is called when a gesture is done by the user. Here is the full code for the function: (Note that the NSLog writes out the correct information.
- (void)handlePanFrom:(UIPanGestureRecognizer *)recognizer {
if (recognizer.state == UIGestureRecognizerStateEnded) {
CGPoint velocity = [recognizer velocityInView:recognizer.view];
NSLog(#"Vel: %f, newPos: %f",velocity.x,velocity.y);
b2Vec2 force = b2Vec2(30, 30);
_body->ApplyLinearImpulse(force, _ballBodyDef->position);
}
}
The force you are applying in handlePanFrom is always b2Vec2(30, 30). It will never change with your current code, and is therefore not going to move in your direction.
Related
I'm having a bit of a problem solving this trivially-looking feature. In my game, at some point in a level, I stop the main game loop and want to zoom to the player sprite. The player sprite is added to a layer that contains this loop and run the code to zoom to this player.
It looks like this :
-(void) stopGameAndZoomToPlayer {
[gamePlayLoop_ invalidate];
zoomToPlayerLoop_ = [NSTimer scheduledTimerWithTimeInterval:1.0f/60.0f target:self selector:#selector(tickZoomToPlayerLoop:) userInfo:nil repeats:YES];
}
The tick method, is for now implemented like this :
-(void) tickZoomToPlayerLoop:(NSTimer*)timer {
if (self.scale > 4) {
[zoomToPlayerLoop_ invalidate];
}
[self setScale:self.scale+0.001];
CGSize winSize = [[CCDirector sharedDirector]winSize];
CGPoint targetPosition = playerSprite_.position;
float wantedX = ((winSize.width/2-targetPosition.x)/self.scale);
float wantedY = ((winSize.height/2-targetPosition.y)/self.scale);
CGPoint maximumCenter = ccp(wantedX,wantedY);
[self setPosition:maximumCenter];
}
Seems trivial right ? Yet, there's something I must be missing because the zoom, while slow, is offset vis-a-vis the player sprite. The player sprite, at the end of the tickZoomToPlayerLoop timer, appears in the top right corner of the screen ; it is not in the center (but not even centered of the top right corner of the viewport).
The way I see it, this code put the center of the main layer to the position of the player sprite. Then it scales. Actually the position shouldn't be in the zoom loop but I put it here because I'll need to handle the boundaries of the level layer, because as for now the user can see the black void of non playable zone, outside the level. Yet, even if the center of the main layer at the beginning of the loop seems to be the player sprite, when scaling, one can see it is not.
Does the scale is targeted to the center of a CCNode ? Is it offseted in any way ? Does the anchor point plays a part in the way the scaling is done ?
Some more infos :
the anchor point of the main layer is (0.5,0.5) - the default one
the position of the main layer is, at first before the timer, (0,0) - simply added when creating the scene
Scaling to my knowledge is effected by anchor points.
If all you need to do is zoom in way not use CCCamera?
[myLayer.camera setEyeX:0 eyeY:0 eyeZ:zoomValue];
You can change the eyeZ to zoom in and out.
I need a way to create a collide effect, without the actual collision between the two images. Let me explain in more detail... If I have one fixed image and one image that is moving both images are on the same x coordinate at different positions. Basically I want the images appear to be colliding.I would want to run a check on the moving image like this...
If (front of moving image is clear)
{[move forward];}
else
{[stop];}
How would I implement this in code??? So that right before the moving image collides into the fixed image it stops, so that they appear to have collided.This check would also be running on a 1/60 NSTimer.
Any advice is welcome. Thank you.
Assuming the object is moving from the left
#define PIXELS_PER_FRAME 1
-(CGFloat) getCurrentX:(UIImage*)image
{
return image.frame.origin.x + image.frame.size.width;
}
-(void) moveImageToStableImage
{
CGFloat xTarget = stableImage.frame.origin.x;
if([self getCurrentX:movingImage] < xTarget)
{
movingImage.frame.origin.x += PIXELS_PER_FRAME;
[self performSelector:#selector(moveImageToStableImage) withObject:nil afterDelay:1.0/60];
}
}
But truth be told in this situation you would probably just be better off using an animation
Me again. I have a simple question. I have an UIImageView like the one shown below.
alt text http://img683.imageshack.us/img683/1999/volumen.png
That UIimageView is supposed to be the knob to control the volume of my iphone project. My question is, how to know the positions of bar on the UIImageView when it is rotated? Because the volume needs to be 0.5 when the little bar on the cercle is vertical.
I got a piece of code which is (in the touchMoved method):
float dx = locationT.x - imgVVolume.center.x;
float dy = locationT.y - imgVVolume.center.y;
CGFloat angleDif = 0.0f;
movedRotationAngle = atan2(dy,dx);
if (beganRotationAngle == 0.0) {
beganRotationAngle = movedRotationAngle;
initialTransform = imgVVolume.transform;
}
else {
angleDif = beganRotationAngle - movedRotationAngle;
CGAffineTransform newTrans = CGAffineTransformRotate(initialTransform, -angleDif);
imgVVolume.transform = newTrans;
}
Help please.
It depends on what input mechanism you want to use to control the rotation.
If the knob is to rotate based on a single finger touch dragging from side to side then you can create a UIPanGestureRecognizer and attach it to the knob UIImageView. The translationInView: method returns a CGPoint which is the amount of X and Y movement from the touch-down point. You can feed that into a formula like the one you post to get an angle of rotation. You'll want to keep track of delta from last position and also check for stop limits (like 0..360) to prevent over-rotation.
OTOH, if you're going to use two finger rotation then you'll want to use a UIRotationGestureRecognizer and look for the rotation value. Just feed that into a CGAffineTransformRotate and set it to the UIImageView transform. That takes care of all of the above for you. Again, you'll want to check for stop limits.
I have a UIView doing a simple animation. It adjusts its y position from 100 to 130 and then reverses. I want it to keep repeating so I have the repeat counter set to 999. Upon user input, I want to take the same UIView and adjust the x position. This is done by means of another UIView animation. The problem is that when the 2nd animation starts, the 1st animation (that goes from 100 to 130 in the y direction) just ends abruptly (as I read that it should). Is there any way to get the final position of the y coordinate of that UIView before it was ended? I would ideally like to have the UIView stay in the same y position that it was in while I translate the x coordinates.
Summary: UIView moves in the y direction from 100-130, reverses and repeats until user input is received. Once received, animation is cut short and UIView jumps to y=130. I would like a way to find out what the final y value was before the animation was cut short, so when new animation with x translation is used, the UIView will not jump to 130, but remain the same position it was in when the 1st animation ended.
I can't seem to see anything that would let you do that. It appears to me that once you set the animation in motion with UIView, then it (and all current state changes) are out of your hands and will only be "returned" to your control and availability once the animation is done and at the designated end point. Is this correct? Any insight would be appreciated. Thank you for your time.
You're looking for the "presentation layer".
Each UIView is rendered using a Core Animation layer, which is accessible from UIView's layer property.
CALayer has a presentationLayer method, which returns a CALayer that represents "a close approximation to the version of the layer that is currently being displayed".
So, to get the current position of your view:
CGRect currentViewFrame = [[myView.layer presentationLayer] frame];
I'm not sure if this is exactly what you want, but UIView's setAnimationBeginsFromCurrentState: used inside a beginAnimations block will cause the x animation to start wherever the y is in progress.
Perhaps for what you are trying to accomplish it would benefit to exercise a little more control over the animation. For this task I would suggestion using an NSTimer scheduled at whatever interval works best for you (1/30 to 1/60) and just adjust the UIView position every time the timer fires. This way you can always access the X and Y components of the view's position.
Something like:
- (void)timerFired:(NSTimer *)timer {
CGPoint p = view.center;
if (p.y >= 130.0) {
positiveMovement = NO;
}
else if (p.y <= 100.0) {
positiveMovement = YES;
}
if (positiveMovement)
p.y++;
else
p.y--;
view.center = p;
}
positiveMovement would just be a BOOL instance variable. You could also then just directly adjust the X value of the view's position elsewhere with user input and it would update accordingly.
On iPhone, how to implement rotating image around the center point using finger touch ?
Just like wheel, if you put finger on the iPhone screen , then move suddenly, then the image becoming rotating around center point just like the wheel, after a while, it becomes more and more slow , finally stop.
Who can help to give some pieces of codes (Object-C) or some suggest ?
I was working with a "spin the bottle"-app yesterday. On the window I have a ImageView with an bottle that's suppose to response to touches and rotate the way the user swipes his finger. I struggled to get my ImageView to rotate during the touch-events (TouchesBegan, Touchesoved, TouchesEnd). I used this code in TouchesMoved to find out the angle in witch to rotate the image.
public override void TouchesMoved (NSSet touches, UIEvent evt)
{
PointF pt = (touches.AnyObject as UITouch).LocationInView(this);
float x = pt.X - this.Center.X;
float y = pt.Y - this.Center.Y;
double ang = Math.Atan2(x,y);
// yada yada, rotate image using this.Transform
}
THIS IS IMPORTANT! When the ImageView rotates, even the x & y-coordinates changes. So touching the same area all the time would give me different values in the pt and prePt-points. After some thinking, googeling and reading I came up with an simple solution to the problem. The "SuperView"-property of the ImageView.
PointF pt = (touches.AnyObject as UITouch).LocationInView(this.SuperView);
Having that small change in place made it alot easier, no i can use the UITouch-metohs LocationInView and PreviousLocationInView and get the right x & y coordinates. Her is parts of my code.
float deltaAngle;
public override void TouchesMoved (NSSet touches, UIEvent evt)
{
PointF pt = (touches.AnyObject as UITouch).LocationInView(this.Superview);
float x = pt.X - this.Center.X;
float y = pt.Y - this.Center.Y;
float ang = float.Parse(Math.Atan2(dx,dy).ToString());
//do the rotation
if (deltaAngle == 0.0) {
deltaAngle = ang;
}
else
{
float angleDif = deltaAngle - ang;
this.Transform = CGAffineTransform.MakeRotation(angleDif);
}
}
Hope that helped someone from spending hours on how to figure out how to freaking rotate a bottle! :)
I would use the affine transformations - yuou can assign a transformation to any layer or UI element using the transform property.
You can create a rotation transform using CGAffineTransform CGAffineTransformMakeRotation( CGFloat angle) which will return a transformation that rotates an element. The default rotation should be around the centerpoint.
Be aware, the rotation is limited to 360 degrees, so if you want to rotate something more than that (say through 720 degrees) - you have to break the rotation into several sequences.
You may find this SO article useful as well.
The transform property of a view or layer can be used to rotate the image displayed within. As far as the spinning part goes, you just track the location and movement of touches in your view with touchesBegan, touchesMoved, and touchesEnded.
Use the distance and time between the touches updates to calculate a speed, and use that to set a rotational velocity. Once you start the image spinning, update the position periodically (with an NSTimer, maybe), and reduce the rotational velocity by some constant.