I have some code that causes the box2d physics simulation to stutter forever after this code is called once. I ran a performance test on it and OSSpinLockLock has a lot of time spent on it. b2Island::Solve and some other box2d functions are causing this to take up so much time. I'm not really sure what is going on here. The effects of this seem to be worse on maps with more overlapping static bodies then maps with less overlapping static bodies. The code that causes the stutter is the following:
for (b2Body*b = currentWorld->GetBodyList(); b!=nil; b = b->GetNext()) {
float distance = 0;
float strength = 0;
float force = 0;
float angle = 0;
CGPoint curPos = [Helper toPixels:b->GetWorldCenter()];
distance = ccpDistance(selfPos, curPos);
if (distance>maxDistance) {
distance = maxDistance - 0.01;
}
//strength = (maxDistance - distance) / maxDistance;
strength = (distance - maxDistance)/maxDistance;
force = strength * maxForce;
angle = atan2f(selfPos.y - curPos.y, selfPos.x - curPos.x);
//b2Vec2 forceVec = [Helper toMeters:force];
//CCLOG(#"strength = %f force = %f angle = %f distance = %f",strength,angle,force, distance);
b->ApplyLinearImpulse(b2Vec2(cosf(angle) * force, sinf(angle) * force), b->GetPosition());
BodyNode * bn = (BodyNode*)b->GetUserData();
if ([bn isKindOfClass:[Soldier class]]) {
((Soldier*)bn).health-=abs(force*(damage * kRocketDamageFactor)); //used to be 50
}
if ([bn isKindOfClass:[BaseAI class]]) {
((BaseAI*)bn).health-=abs(force*(damage * kRocketDamageFactor));
}
if ([bn isKindOfClass:[BaseLevelObject class]]) {
if (((BaseLevelObject*)bn).takesDamageFromBullets == YES) {
((BaseLevelObject*)bn).health-=abs(force*(damage * kRocketDamageFactor));
}
}
I suspect that the ApplyLinearImpulse part is what is causing the stutter because it is the only thing related to physics. I just commented out this whole loop and the stutter never came. But as soon as I exploded some other explosives with the same code, the stutter came. Do overlapping static b2body objects slow the physics simulation down?
The issue was caused by the code giving all the bodies that were farther away than the max distance a small tap towards the explosion. I'm not really sure why this would cause the physics simulation to stutter, but adding a continue statement in place of distance = maxDistance - 0.01; solved the problem.
Related
I wanted to create a space background so I make a for loop to create the stars. Here is the code:
for (int i = 0; i<100; i++) {
SKShapeNode *star= [SKShapeNode shapeNodeWithPath:Path.CGPath];
star.fillColor = [UIColor whiteColor];
star.physicsBody = nil;
int xposition = arc4random()%960;
int yposition = arc4random()%640;
star.position = CGPointMake(xposition, yposition);
float size = (arc4random()%3 + 1)/10.0;
star.xScale = size;
star.yScale = size;
star.alpha = (arc4random()%10 + 1 )/ 10.0;
star.zPosition = -2;
[self addChild:star];
}
But it takes a lot from my cpu. when the code is activated the cpu at top 78%.(I check the code in the iPhone simulator);
Somebody know how to fix it? thanks.
Your physics bodies continue to calculate even when off of the screen. You will need to remove them once they go out of the frame, otherwise everything will slow to a crawl. (And to echo what others have stated you will eventually need a real device).
From this document: Jumping Into Sprite Kit
You can implement the "Did Simulate Physics" method to get rid of the stars that fell from the bottom of the screen like so:
-(void)didSimulatePhysics
{
[self enumerateChildNodesWithName:#"star" usingBlock:^(SKNode *node, BOOL *stop) {
if (node.position.y < 0)
[node removeFromParent];
}];
}
Note that you will first need to set the name of your star shapes by using the name property like so:
star.name = "star"
Like many that post about this topic, I too am busy trying to write myself an accurate simulator for the movement of objects in a 2D gravitation field.
I decided early on that I would settle on Velocity Verlet Integration, as I want my objects to maintain stable orbits and conserve energy even if the timestep is rather large. So, what might the problem be?
Well, so far, everything seems to behave correctly, except for one component. When I try to calculate the correct velocity for a stable orbit at a certain distance, the resulting velocity sends them into odd elliptical orbits that quickly increase in magnitude each time.
So, to begin, here are the following methods that determine an objects next position, velocity, and acceleration in scene: (Objective C)
Acceleration:
-(CGVector)determineAccelerationFor:(SKObject *)object
{ // Ok, let's find Acceleration!
CGVector forceVector = (CGVector){0,0}; // Blank vector that we will add forces to
for (SKObject *i in self.sceneObjects)
{
if (![i isEqual:object]) // Just make sure we're not counting ourselves here
{
CGPoint distance = [self getDistanceBetween:i.position And:object.position];
float hypotenuse = sqrtf(powf(distance.x, 2)+ powf(distance.y, 2));
float force = ((self.gravity * object.mass * i.mass)/powf(hypotenuse, 3));
float xMagnitude = (force * distance.x);
float yMagnitude = (force * distance.y);
forceVector.dx += xMagnitude;
forceVector.dy += yMagnitude;
}
}
CGVector acceleration = (CGVector){forceVector.dx/object.mass, forceVector.dy/object.mass};
return acceleration;
}
Cool, so basically, I just take an object, add all the other forces that each other object imposes on it together then divide the X & Y factor by the mass of the current object to get the acceleration!
Next up is Velocity. Here I use the following equation:
The method for it is pretty straightforward too:
-(CGVector)determineVelocityWithCurrentVelocity:(CGVector)v OldAcceleration:(CGVector)ao NewAcceleration:(CGVector)a
{
float xVelocity = (v.dx + ((ao.dx + a.dx)/2) * self.timeStep);
float yVelocity = (v.dy + ((ao.dy + a.dy)/2) * self.timeStep);
CGVector velocity = (CGVector){xVelocity,yVelocity};
return velocity;
}
And finally, position! The equation for this is:
And it is determined with the following method!
-(CGPoint)determinePositionWithCurrentPosition:(CGPoint)x CurrentVelocity:(CGVector)v OldAcceleration:(CGVector)ao
{
float xPosition = (x.x + v.dx * self.timeStep + ((ao.dx * powf(self.timeStep, 2))/2));
float yPosition = (x.y + v.dy * self.timeStep + ((ao.dy * powf(self.timeStep, 2))/2));
CGPoint position = (CGPoint){xPosition,yPosition};
return position;
}
This is all called from the below method!!
-(void)refreshPhysics:(SKObject *)object
{
CGPoint position = [self determinePositionWithCurrentPosition:object.position CurrentVelocity:object.velocity OldAcceleration:object.acceleration]; // Determine new Position
SKAction *moveTo = [SKAction moveTo:position duration:0.0];
[object runAction:moveTo]; // Move to new position
CGVector acceleration = [self determineAccelerationFor:object]; // Determine acceleration off new position
CGVector velocity = [self determineVelocityWithCurrentVelocity:object.velocity OldAcceleration:object.acceleration NewAcceleration:acceleration];
NSLog(#"%# Old Velocity: %f, %f",object.name,object.velocity.dx,object.velocity.dy);
NSLog(#"%# New Velocity: %f, %f\n\n",object.name,velocity.dx,velocity.dy);
[object setAcceleration:acceleration];
[object setVelocity:velocity];
}
Okay, so those methods above dictate how objects are moved in scene. Now onto the initial issue, the ever present problem of achieving a stable orbit!
In order to determine what velocity an object should have to maintain an orbit, I use the following equation:
And I implement that as follows:
-(void)setObject:(SKObject *)object ToOrbit:(SKObject *)parent
{
float defaultSeparation = 200;
// Move Object to Position at right of parent
CGPoint defaultOrbitPosition = (CGPoint){parent.position.x + (parent.size.width/2)+ defaultSeparation,parent.position.y};
[object setPosition:defaultOrbitPosition];
// Determine Orbital Velocity
float velocity = sqrtf((self.gravity * parent.mass)/(parent.size.width/2+defaultSeparation));
CGVector vector = (CGVector){0,velocity};
[object setVelocity:vector];
}
And for some reason, despite this, I get abysmal results. Here is some of the output:
Information:
Gravity(constant) = 1000 (For test purposes)
Mass(Parent) = 5000 units
Mass(Satellite) = 1 units
Separation = 224 pixels
It determines that in order for the Satellite to Orbit the Parent, a velocity of:
149.403580 pixels/timeStep
is required. And that checks out on my calculator.
So this has left me a little confused as to what could be going wrong. I log all the output concerning new velocities and positions, and it does use the velocity I set it to, but that just doesn't seem to make a difference. If anyone could possible help spot what's going wrong here I would be immensely grateful.
If anyone believes I have left something out, tell me and I will edit this right away. Thanks!
I want to move an object from a random point just outside of the view in a Sprite Kit game.
The logical way of doing this would be to create a rectangle 100px (example) bigger than the view, and pick a random point on it's perimeter. Unfortunately, I don't know an easy way to do this.
How can I easily create a random point on the perimeter of a rectangle (which is slightly bigger than my view)?
Update
This should do what you want:
- (CGPoint)randomPointOutsideRect:(CGRect)rect withOffset:(CGFloat)offset {
NSUInteger random = arc4random_uniform(4);
UIRectEdge edge = 1 << random; // UIRectEdge enum values are defined with bit shifting
CGPoint randomPoint = CGPointZero;
if (edge == UIRectEdgeTop || edge == UIRectEdgeBottom) {
randomPoint.x = arc4random_uniform(CGRectGetWidth(rect)) + CGRectGetMinX(rect);
if (edge == UIRectEdgeTop) {
randomPoint.y = CGRectGetMinY(rect) - offset;
}
else {
randomPoint.y = CGRectGetMaxY(rect) + offset;
}
}
else if (edge == UIRectEdgeLeft || edge == UIRectEdgeRight) {
randomPoint.y = arc4random_uniform(CGRectGetHeight(rect)) + CGRectGetMinY(rect);
if (edge == UIRectEdgeLeft) {
randomPoint.x = CGRectGetMinX(rect) - offset;
}
else {
randomPoint.x = CGRectGetMaxX(rect) + offset;
}
}
return randomPoint;
}
This should be fairly straightforward, let me know if there's something unclear.
Basically, we pick one edge at random, then "fix" one axis and pick a random value on the other (within the width/height boundaries).
arc4random_uniform gives us only integers, but that's fine because floating point values in frames are bad when displaying stuff on screen.
There is probably a shorter way to write this; feel free to edit to improve, everyone.
Original answer
How can I easily create a point 100 pixels away from the edge of my view?
With CGRectOffset().
Assuming you want a CGPoint 100pt "higher" (ie. with a lower y) than your view, do:
CGRect viewFrame = // lets say for this example that your frame is at {{20, 40}, {300, 600}}
CGRect offsetFrame = CGRectOffset(viewFrame, 0, -100);
CGPoint offsetPoint = offsetFrame.origin
// offsetPoint = {20, -60}
I'm pretty new to iOS and cocos2d and I'm having a problem trying to create what I want the code to do. Let me give you the rundown first then i'll show what I've got.
What I got so far is a giant sprite in the middle and when that is touched, I want to have say 2000 of a different sprite generate from the center position and like a particle system, shoot off in all directions.
First off, I tried coding implementing the velocity code (written in Objective-c) over to Cocos2d and that didn't work. -code-
-(void)ccTouchBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
if(CGRectContainsPoint([[self getChildByTag:1] boundingBox], location))
{
for( int i = 0; i < 100; i++)
{
CCSprite *ballGuySprite = [CCSprite spriteWithFile:#"ball.png"];
[self addChild:ballGuySprite z:7];
ballGuySprite.position = ccp(((s.width + i *10) /2), (s.height + i *10) /2);
}
}
}
What that does is when I touch the first sprite, 100 of the other sprites are on top of each other leading to the top right corner.
The velocity code that I used when as followed and when I try to apply it to the sprite nothing happens. - Velocity code -
-(void) checkCollisionWithScreenEdges
{
if(ballGuysRect.origin.x <= 0)
{
ballVelocity.x = abs(ballVelocity.x);
}
if(ballGuysRect.origin.x >= VIEW_WIDTH - GUY_SIZE)
{
ballVelocity.x = -1 * abs(ballVelocity.x);
}
if(ballGuysRect.origin.y <= 0)
{
ballVelocity.y = abs(ballVelocity.y);
}
if(ballGuysRect.origin.y >= VIEW_HEIGHT - GUY_SIZE)
{
ballVelocity.y = -1 * abs(ballVelocity.y);
}
}
-(void) updateModelWithTime:(CFTimeInterval)timestamp
{
if(lastTime == 0.0)
{
lastTime = timestamp;
}
else
{
timeDelta = timestamp - lastTime;
lastTime = timestamp;
ballGuysRect.origin.x += ballVelocity.x * timeDelta;
ballGuysRect.origin.y += ballVelocity.y * timeDelta;
[self checkCollisionWithScreenEdges];
}
}
When I attach that code to the sprite, nothing happen.
I also tried adding a CCParticleExplosion which did do what I wanted but I still want to add a touch function to each individual sprite that's generated and they tend to just fade away.
So again, I'm still fairly new to this and if anyone could give any advice that would be great.
Thanks for your patients and time to read this.
Your code looks good to me, but you never seem to update the position of your sprites. Somewhere in updateModelWithTime I would expect you to set ballGuySprite.position = ballGuysRect.origin plus half of its height or width, respectively.
Also, I don't see how updateModelWithTime can control 100 different sprites. I see only one instance of ballGuysRect here. You will need a ballGuysRect for each sprite, e.g. an array.
Finally, I'd say that you don't really need ballGuysRect, ballVelocity, and the sprite. Ball could be a subclass of CCSprite, including a velocity vector. Then all you need to do is keep an array of Balls and manage those.
I am not sure what version of cocos2d you are using but a few things look a bit odd.
Your first problem appears to be that you are just using the same sprite over and over again.
Since you want so many different sprites shooting away, I would recommend that you use a CCSpriteBatchNode, as this should simplify things and speed things up.
The following code should help you get that set up and move them offscreen with CCMoveTo:
//in your header file:
CCSpriteBatchNode *batch;
//in your init method
batch = [CCSpriteBatchNode batchNodeWithFile:#"ball.png"];
//Then in your ccTouches method
for( int i = 0; i < 100; i++)
{
CCSprite *ballGuySprite = [CCSprite spriteWithFile:#"ball.png"];
[batch addChild:ballGuySprite z:7 tag:0];
ballGuySprite.position = ccp(where-ever the center image is located);
id actionMove = [CCMoveTo actionWithDuration:actualDuration
position:ccp(random off screen location)];
[ballGuySprite runAction:actionMove];
}
Also usually your update method looks something like the following:
-(void)update:(ccTime)delta{
//check for sprites that have moved off screen and disable them.
}
Hope this helps.
I'm animating a UIView by updating its anchorpoint 60 times a second using an NSTimer.
The location of the UIView changes depending on its angle, so it always appears to be down relative to the device...
However, the NSTimer doesn't fire precisely 60 times a second. It's always a little off, causing jerky animation. I've searched this a lot, I know a bit about delta time, but I don't know how to apply it to my situation.
Here's the movement code I'm using:
float rotation = 0;
if (leftSideIsBeingHeldDown) {
rotation += (0.05f/rotationFactor);
} else if (rightSideIsBeingHeldDown) {
rotation -= (0.05f/rotationFactor);
}
movementX += -sinf(rotation);
movementY += -cosf(rotation);
float finalX = 0.0001 * movementX;
float finalY = 0.0001 * movementY;
mapView.layer.anchorPoint = CGPointMake(finalX, finalY);
mapView.transform = CGAffineTransformMakeRotation(rotation);
Does anyone know how to apply delta time to this?
You might want to look into the CADisplayLink class which provides you a timer that is tied to the display refresh rate. It should be a better solution than an NSTimer in this case.
Additionally, you need to remember the time of each "tick" and calculate the rotation or movement that should have been done since the last tick. For example (pseudo-code):
- (void)displayLinkTick:(id)sender
{
NSTimeInterval timespan;
NSDate *now;
now = [NSDate date];
if (myPreviousTick) {
timespan = [now timeintervalSinceDate:myPreviousTick];
} else {
// The very first tick.
timespan = 0;
}
// Calculate the angle according to the timespan. You need a
// value that specifies how many degrees/radians you want to
// revolve per second and simply multiply that with the timespan.
angle += myRadiansPerSecond * timespan;
// You'd do the same with the position. I guess this involves
// minor vector math which I don't remember right now and am
// too lazy to look up. You need to have a distance per second
// which you multiply with the timespan. Together with the
// direction vector you can calculate the new position.
// At the end, remember when this tick ran.
[myPreviousTick release];
myPreviousTick = [now retain];
}
You want to record the time you last rotated, and the difference in time between then and now, and use that to work out a factor, which you can use to adjust the rotation and x/y values.
for example:
NSDate now = [NSDate now];
timeDiff = now - lastRotateTime;
factor = timeDiff / expectedTimeDiff;
x = x + xIncrement * factor;
y = y + yIncrement * factor;
angle = angle + angleIncrement * factor;
There are many better examples on game dev forums, which explain it in more detail.