i use following code to move my Box2D object into screen, but because gravity of my world or something else i dont know why my objects is forced to move down, i am new to box2d.
i want to move my object in entire world without gravity.
-(void) tick:(NSTimer *)timer {
int32 velocityIterations = 8;
int32 positionIterations = 1;
world->Step(1.0f/60.0f, velocityIterations, positionIterations);
for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
{
if (b->GetUserData() != NULL)
{
UIView *oneView = (UIView *)b->GetUserData();
CGPoint newCenter = CGPointMake(b->GetPosition().x * PTM_RATIO,self.view.bounds.size.height - b->GetPosition().y * PTM_RATIO);
oneView.center = newCenter;
CGAffineTransform transform = CGAffineTransformMakeRotation(- b->GetAngle());
oneView.transform = transform;
}
}
}
my accelerometer code is as follow.
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {
b2Vec2 gravity;
gravity.Set( acceleration.x * 1.81, acceleration.y * 1.81 );
world->SetGravity(gravity);
}
pleas if any one work around.
Thanks.
As i understand you want to move your object setting it's position. It's a bad idea because it will provide non-physical behavior of the bodies colliding with your object. That's because if you will only change the position of your body it's velocity for physics engine will be still zero and collision will be processed according to zero speed of your object.
A better solution is to use b2_kinematicBody type for your object. Then you will be able to control it's motion specifying it's velocity vector and physics will behave as expected. Also the gravity (and no other forces) will not be applied to your object because of it's type.
EDIT
//creation
b2BodyDef bDef;
bDef.type = b2_kinematicBody;
bDef.position.Set(5, 6);
b2Body *body = physWorld->CreateBody(&bDef);
//control
body->SetLinearVelocity(b2Vec2(3, 4));
Related
I'm using accelerometer in my first Cocos2D game and it work fine, i'm able to move the sprite using the below code however, when i change the orientation from landscapeLeft to landscapeRight, the sprite stops responding to Y coordination, and the sprite goes to the top of the screen and doesn't properly respond... I believe it's because of changing the device orientation, but i'm not sure since i'm pretty new to App Development, any help will be appreciated.
Here is the sample code i'm using...
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration
{
//this determines how sensitive the accelerometer reacts (higher = more sensitive)
NSUserDefaults *defaulObj = [NSUserDefaults standardUserDefaults];
float sensitivity = [defaulObj floatForKey:#"Sensitivity"]; //10.0f
if (!sensitivity) {
sensitivity = 6;
}
// this controls how quickly the velocity decelerates (lower = quicker to change direction)
float deceleration = 0.4f;
static float xVal = 0;
if (!self.isFlag) {
xVal = -acceleration.x;
self.isFlag = TRUE;
}
playerVelocity.x = playerVelocity.x * deceleration + (xVal + acceleration.x) * sensitivity;
playerVelocity.y = playerVelocity.y * deceleration + acceleration.y * sensitivity;
playerVelocity.y = playerVelocity.y*-1;
}
Perhaps this helps out, flips Y along your current device orientation.
float rotatedY = acceleration.y;
if ([UIApplication sharedApplication].statusBarOrientation==UIInterfaceOrientationLandscapeLeft) {
rotatedY *= -1;
}
then use rotatedY insteat of acceleration.y
I've been reading a book on the cocos2d framework for ios5 for a few days and have developed a small game that the book walks you through. To control the sprite in this game you use the accelerometer:
-(void) accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration
{
float deceleration = 0.4f;
float sensitivity = 6.0f;
float maxVelocity = 100;
// adjust velocity based on current accelerometer acceleration
playerVelocity.x = playerVelocity.x * deceleration + acceleration.x * sensitivity;
// we must limit the maximum velocity of the player sprite, in both directions (positive & negative values)
if (playerVelocity.x > maxVelocity)
{
playerVelocity.x = maxVelocity;
}
else if (playerVelocity.x < -maxVelocity)
{
playerVelocity.x = -maxVelocity;
}
// Alternatively, the above if/else if block can be rewritten using fminf and fmaxf more neatly like so:
// playerVelocity.x = fmaxf(fminf(playerVelocity.x, maxVelocity), -maxVelocity);
}
Now I'm wondering if I can change this code to allow the sprite to still accelerate/decelerate along the x axis, but to use touch input rather than the accelerometer, and to go faster the longer the touch is held down for? So a touch to the right would move the sprite to that spot slowly, if the touch is released, it stops moving to that spot. The longer a touch is held down, the faster the sprite moves.
is there anything in the framework to allow me to implement a rotation mechanism that allows my sprite to rotate to the position that the touch was in, so it looks like its facing the point thats been touched?
Well, afaik theres no method that will determine the angle to the touch and then rotate the sprite accordingly, but if you have the x and y coordinates of the sprite and the touch you can calculate it yourself fairly easily.
CGPoint spriteCenter; // this should represent the center position of the sprite
CGPoint touchPoint; //location of touch
float distanceX = touchPoint.x - spriteCenter.x;
float distanceY = touchPoint.y - spriteCenter.y;
float angle = atan2f(distanceY,distanceX); // returns angle in radians
// do whatever you need to with the angle
Once you have the angle you can set the rotation of the sprite.
I am making an iphone app where a ball will roll around the screen based on how the user tilts the device. If the device is lies flat on the table theoretically the ball would not move. If the device is tilted standing completely upward the I want the ball to roll straight down at maximum speed. The speed depends on how far from the flat position the device is tilted. Also, it also works for if the user tilts right or left or up or combinations of the four. I am using the accelerometer right now and the ball moves and it works okay, I am just not real familiar with physics. If someone has any suggestions on how to get this to work smoothly please let me know.
Thanks!
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration
{
float xx = -[acceleration x];
float yy = [acceleration y];
float z = -[acceleration z];
z = 1 - z;
NSString * zaxis = [NSString stringWithFormat:#"%f", z];
lblz.text = zaxis;
lbly.text = [NSString stringWithFormat:#"%f", yy];
lblx.text = [NSString stringWithFormat:#"%f", xx];
CGFloat newx;
CGFloat newy;
if (yy > 0)
{
newy = ball.center.y - ((1 - yy) * z);
}
else
{
newy = ball.center.y + ((1 - yy) * z);
}
if (xx > 0)
{
newx = ball.center.x - ((1 - xx) * z);
}
else
{
newx = ball.center.x + ((1 - xx) * z);
}
CGPoint newPoint = CGPointMake(newx, newy);
ball.center = newPoint;
If you want to make it look more realistic and leverage existing stuff, look at some of the existing physics engines and 2d frameworks, Box2d and Cocos2d, but there are many others.
I think the key thing you are messing here is the difference between acceleration and velocity. You want the 'amount of tilt' to work as an acceleration. Each frame the balls Velocity should change by the acceleration, then the balls position should change by the balls velocity.
So just in X it should be something like:
float accelX = acceleration.x;
mVel.x += accelX; \\mVel is a member variable you have to store
ball.center.x += mVel.x;
---More Complex version
Now the more I think about it, it might not be the 'amount of tilt' you want to be the acceleration. You might want the amount of tilt to be the 'Target Velocity.' But you still want to use an acceleration to get there.
mTargetVel.x = acceleration.x;
//Now apply an acceleration to the velocity to move towards the Target Velocity
if(mVel.x < mTargetVel.x) {
mVel.x += ACCEL_X; //ACCEL_X is just a constant value that works well for you
}
else if(mVel.x > mTargetVel.x) {
mVel.x -= ACCEL_X;
}
//Now update the position based on the new velocity
ball.center.x += mVel.x;
I'm adding an enemy like this:
-(void)addEnemy {
if ([spawnedEnemies count] < 25) {
CCSprite* sprite = [CCSprite spriteWithFile:#"white.png"];
float randomX = arc4random() % 480;
float randomY = arc4random() % 320;
sprite.position = ccp(randomX,randomY);
[spawnedEnemies addObject:sprite];
[self addChild:sprite];
[sprite runAction:[CCMoveTo actionWithDuration:5 position:player.position]];
} }
but if my player moves the sprite still moves to the last player position...
because of that i tried this in my tick:
-(void)tick:(ccTime)delta {
for (CCSprite *sp in spawnedEnemies) {
[sp stopAllActions];
[sp runAction:[CCMoveTo actionWithDuration:5
position:player.position]];
} }
but the enemies will only move if i stop moving (there just moving reallllllllyyyyyyyyy slow because every time i move it calls [sp stopAllActions]
What should I do now?
EDIT:*EDIT:*EDIT:*EDIT:*EDIT:*EDIT:*EDIT:*EDIT:*EDIT:
Now I'm doing this and the enemies are moving to the player even if the player is moving
but there's a problem: the nearer the enemy (is to the player) the slower they are moving...
How to solve this?
//function to apply a velocity to a position with delta
static CGPoint applyVelocity(CGPoint velocity, CGPoint position, float delta){
return CGPointMake(position.x + velocity.x * delta, position.y + velocity.y * delta);
}
-(void)tick:(ccTime)delta {
for (CCSprite *sp in spawnedEnemies) {
CGPoint m = ccpSub(player.position, sp.position);
sp.position = applyVelocity(m, sp.position, 1.0/60.0f);
}
}
I have four ideas:
Schedule a new update selector with a lower frequency and move the enemies in that method: [self schedule:#selector(moveEnemies) interval:0.1];
Only move the enemies when the player.position changes, maybe in your ccTouchesMoved-method.
Instead of using CCActions, set the position of the sprite directly, you need to do some vector-computations.
Use a physics-engine like Box2D (included in Cocos2D SDK). Then you can simply apply a force to each enemy to the direction of the player in each step.
EDIT:
In order to move the enemies with constant velocity, normalize the velocity vector m:
m = ccpMult(ccpNormalize(m), kSpeed);
kSpeed is a constant float value to adjust the speed.
Hope that helps...
I am trying to change my Sprite anchor point so that I can rotate over a 0.0f,0.0f anchorpoint. At first my object is rotation at the default anchor point (0.5f,0.5f). However later on I need it to rotate over a 0.0,0.0 AnchorPoint.
The problem is I cannot change the anchor point and change the position accordingly, so it stays on the same position, without the object appearing to quickly move and reposition to its original point.
Is there a way I can set the anchor point and the position of my Sprite at once, without it moving at all?. Thank you.
-Oscar
I found a solution to this with a UIView elsewhere, and rewrote it for cocos2d:
- (void)setAnchorPoint:(CGPoint)anchorPoint forSprite:(CCSprite *)sprite
{
CGPoint newPoint = CGPointMake(sprite.contentSize.width * anchorPoint.x, sprite.contentSize.height * anchorPoint.y);
CGPoint oldPoint = CGPointMake(sprite.contentSize.width * sprite.anchorPoint.x, sprite.contentSize.height * sprite.anchorPoint.y);
newPoint = CGPointApplyAffineTransform(newPoint, [sprite nodeToWorldTransform]);
oldPoint = CGPointApplyAffineTransform(oldPoint, [sprite nodeToWorldTransform]);
CGPoint position = sprite.position;
position.x -= oldPoint.x;
position.x += newPoint.x;
position.y -= oldPoint.y;
position.y += newPoint.y;
sprite.position = position;
sprite.anchorPoint = anchorPoint;
}
This is a good question, and I don't know the full answer yet.
As you may have noticed, the anchorPoint cannot be changed without affecting scale and rotation.
For scaled sprites:
You have to simultaneously change the anchorPoint and position of your sprite. See this question for a hint
For rotated sprites:
Intuition says you would need to simultaneously change anchorPoint, rotation, and position. (I have no idea how to compute this.)
NOTE: I'm still learning graphics programming, so I'm not 100% able to compute this stuff yet.
I've needed this a couple of times and decided to make a extension for CCNode, tested it abit and seems to work fine. Can be really useful to some :)
It's tested with 1.x but It should work fine in 2.x too. Supports transformed nodes and HD.
Just add this to your project and import whenever you need it - It will be added to all classes deriving from CCNode. (CCSprite, CCLayer)
Interface
#import "cocos2d.h"
#interface CCNode (Extensions)
// Returns the parent coordinate for an anchorpoint. Useful for aligning nodes with different anchorpoints for instance
-(CGPoint)positionOfAnchorPoint:(CGPoint)anchor;
// As above but using anchorpoint in points rather than percentage
-(CGPoint)positionOfAnchorPointInPoints:(CGPoint)anchor;
//Sets the anchorpoint, to not move the node set lockPosition to `YES`. Setting it to `NO` is equal to setAnchorPoint, I thought this would be good for readability so you always know what you do when you move the anchorpoint
-(void)setAnchorPoint:(CGPoint)a lockPosition:(BOOL)lockPosition;
#end
Implementation
#import "CCNode+AnchorPos.h"
#implementation CCNode (Extensions)
-(CGPoint)positionOfAnchorPoint:(CGPoint)anchor
{
float x = anchor.x * self.contentSizeInPixels.width;
float y = anchor.y * self.contentSizeInPixels.height;
CGPoint pos = ccp(x,y);
pos = CGPointApplyAffineTransform(pos, [self nodeToParentTransform]);
return ccpMult(pos, 1/CC_CONTENT_SCALE_FACTOR());
}
-(CGPoint)positionOfAnchorPointInPoints:(CGPoint)anchor;
{
CGPoint anchorPointInPercent = ccp(anchor.x/self.contentSize.width, anchor.y/self.contentSize.height);
return [self positionOfAnchorPoint:anchorPointInPercent];
}
-(void)setAnchorPoint:(CGPoint)a lockPosition:(BOOL)lockPosition
{
CGPoint tempPos = [self positionOfAnchorPoint:a];
self.anchorPoint = a;
if(lockPosition)
{
self.position = tempPos;
}
}
#end
Cocos2d-x + Fixed scale
YourClass.h
virtual cocos2d::Vec2 positionFromSprite(cocos2d::Vec2 newAnchorPoint, cocos2d::Sprite *sprite);
YourClass.m
Vec2 YourClass::positionFromSprite(Vec2 newAnchorPoint, cocos2d::Sprite *sprite) {
Rect rect = sprite->getSpriteFrame()->getRect();
Vec2 oldAnchorPoint = sprite->getAnchorPoint();
float scaleX = sprite->getScaleX();
float scaleY = sprite->getScaleY();
Vec2 newPoint = Vec2(rect.size.width * newAnchorPoint.x * scaleX, rect.size.height * newAnchorPoint.y * scaleY);
Vec2 oldPoint = Vec2(rect.size.width * oldAnchorPoint.x * scaleX, rect.size.height * oldAnchorPoint.y * scaleY);
Vec2 position = sprite->getPosition();
position.x -= oldPoint.x;
position.x += newPoint.x;
position.y -= oldPoint.y;
position.y += newPoint.y;
return position;
}