I am making a game using Cocos2D and Kobold2D. In my game, I have a ship that I want to move to where the player taps, using this code:
KKInput * input = [KKInput sharedInput];
CGPoint tap = [input locationOfAnyTouchInPhase:KKTouchPhaseBegan];
if (tap.x != 0 && tap.y != 0)
{
[ship stopAllActions]; // Nullifies previous actions
int addedx = tap.x - ship.position.x;
int addedy = tap.y - ship.position.y;
int squaredx = pow(addedx, 2);
int squaredy = pow(addedy, 2);
int addedSquares = squaredx + squaredy;
int distance = pow(addedSquares, 0.5);
[ship runAction: [CCMoveTo actionWithDuration:distance/100 position:tap]];//makes ship move at a constant speed
}
The ship generally moves as I expect it to. However, if I tap near the ship, instead of smoothly moving to the tap location, it jumps to that location. How do I fix this?
Your logic is right but your calculation is lack precision.
Especially when you calc the fly time as distance/100. That means when distance < 100 the result is 0, so the ship is jumping to the destination.
Basically, you should use float instead of int when dealing with positions in cocos2d. And there are couple functions can do the work nicely.
You may change your code to this:
[ship stopAllActions]; // Nullifies previous actions
float distance = ccpDistance(tap, ship.position);
[ship runAction: [CCMoveTo actionWithDuration:distance/100.0f position:tap]];
First of All you can use the ccpDistance function of cocos2d to calculate distance between two point.
And it jumps because if u tap too near the distance is too small suppose 2 or 10 ... the you are dividing it on 100
e.g 5/100 = 0.05 which is too low that's why it jumps.
You need to handle it manually i think some thing like if(speed<1) speed++; adding 1 to speed. shortcut solution :)
Related
This is language-agnostic question, more about model of my game.
I have a snake game with elements, but I move the elements smoothly, they don't just move 1 block each time, but instead they move some amount of pixels every frame.
I have an update loop that calculates the positions of the element, but I am stuck on correct calculations.
I have heading for each element:
typedef NS_ENUM(int, kElementHeading)
{
kElementHeadingNorth = 1,
kElementHeadingSouth,
kElementHeadingEast,
kElementHeadingWest
};
I also have velocity (x, y) that determines in what direction snake is going. I have problem with snake movement, because my elements are in wrong positions. I managed to localize the thing for 2 elements, but my solution fails on more elements.
First solution I tried is to save point of rotation where the head changes direction. This worked, but due to different circumstances element can move different amount of pixels each turn. Often the element would skip the point. I tried increasing the zone where it should rotate, but it adds up error. I tried fixing this error, but element would still separate from snake (quite often).
On the second try I decided to keep the snake head in center of the screen and move the world around it. It worked good for 2 elements, as I just smoothly move the next element to desired position relatively to head. But this fails badly on more elements. If you make fast turns they start dancing and not following the path.
Third thing that I tried is leaving a path for other elements to follow. But that didn't work because I intend to keep my snake on center of the screen and technically it never moves to create a path.
I'm looking to replicate the movement pattern like in Nimble Quest (or any snake).
How should I implement snake elements moving to have no errors?
Here is my code for the first method, problem with it is that often the elements would fall off. The code is pretty self-explanatory. Rotation points are the places where to change direction.
CFTimeInterval delta = self.lastTime - currentTime;
CGPoint currentPosition = self.playerSnake.head.sprite.position;
CGPoint velocity = self.playerSnake.velocity;
self.playerSnake.head.sprite.position = CGPointMake(currentPosition.x + velocity.x * delta * CONSTANTSPEEDFACTOR , currentPosition.y + velocity.y * delta * CONSTANTSPEEDFACTOR);
for (SnakeElement *element in self.playerSnake.elements) {
CGPoint currentPositionE = element.sprite.position;
CGPoint velocityE = element.velocity;
element.sprite.position = CGPointMake(currentPositionE.x + velocityE.x * delta * CONSTANTSPEEDFACTOR , currentPositionE.y + velocityE.y * delta * CONSTANTSPEEDFACTOR);
}
BOOL markToDelete = NO;
NSDictionary *deleteDictionary;
for (NSDictionary *dict in self.playerSnake.rotationPoints) {
CGPoint positionCoordinate = CGPointFromString(dict[#"position"]);
CGPoint velocityNew = CGPointFromString(dict[#"velocity"]);
double newAngle = [dict[#"angle"] doubleValue];
for (SnakeElement *element in self.playerSnake.elements) {
int xDifference = element.sprite.position.x - positionCoordinate.x;
int yDifference = element.sprite.position.y - positionCoordinate.y;
if ((xDifference > -2 && xDifference < 2) && (yDifference > -2 && yDifference < 2) ) {
element.velocity = velocityNew;
element.sprite.position = CGPointMake(element.sprite.position.x + xDifference, element.sprite.position.y + yDifference);
SKAction *action = [SKAction rotateToAngle:newAngle duration:0.2 shortestUnitArc:YES];
[element.sprite runAction:action];
if ([element isEqual:[self.playerSnake.elements lastObject]]) {
markToDelete = YES;
deleteDictionary = dict;
}
}
}
}
[self.playerSnake.rotationPoints removeObject:deleteDictionary];
If I try increase the catch zone for the turning point, the elements tend to fall off more often then when it is 1 or 2 pixels wide. I'm not sure why this happens.
This is what I was suggesting you do in the comments in terms of handling your turning on points :
1.. calculate the distance that the element should move that frame based on speed and your elapsed time since last frame. (delta)
2.. calculate distance from element's current position to the turn point. This is the beforeDistance I spoke of in the comments
3.. calculate the distance the element should move towards the NEW target turning point AFTER the turn
afterDistance = distanceToMoveThisFrame - beforeDistance
4.. Calculate the new position for your element, starting at the current turning point towards the next target turning point of the element using afterDistance
If you follow this logic, you will NEVER overshoot or undershoot the turning point.
I'm making an app that (among other things) displays a simplified compass image that rotates according to the device's rotation. The problem is that simply doing this:
float heading = -1.0f * M_PI * trueHeading / 180.0f; //trueHeading is always between 0 and 359, never 360
self.compassNeedle.transform = CGAffineTransformMakeRotation(heading);
inside CLLocationManager's didUpdateHeading method makes the animation ugly and choppy.
I have already used Instruments to find out whether its simply my app not being able to render at more than 30-48 fps, but that's not the case.
How can I smooth out the image view's rotation so that it's more like Apple's own Compass app?
Instead of using the current instant value, try using the average of the last N values for the true heading. The value may be jumping around a lot in a single instant but settle down "in the average".
Assuming you have a member variable storedReadings which is an NSMutableArray:
-(void)addReading(float):newReading
{
[storedReadings addObject:[NSNumber numberWithFloat:newReading]];
while([storedReadings count] > MAX_READINGS)
{
[storedReadings removeObjectAtIndex:0];
}
}
then when you need the average value (timer update?)
-(float)calcReading
{
float result = 0.0f;
if([storedReadings count] > 0)
{
foreach(NSNumber* reading in storedReadings)
{
result += [reading floatValue];
}
result /= [storedReadings count];
}
return result;
}
You get to pick MAX_READINGS a priori.
NEXT LEVEL(S) UP
If the readings are not jumping around so much but the animation is still choppy, you probably need to do something like a "smooth" rotation. At any given time, you have the current angle you are displaying, theta (store this in your class, start it out at 0). You also have your target angle, call it target. This is the value you get from the smoothed calcReading function. The error is defined as the difference between the two:
error = target-theta;
Set up a timer callback with a period of something like 0.05 seconds (20x per second). What you want to do is adjust theta so that the error is driven towards 0. You can do this in a couple of ways:
thetaNext += kProp * (target - theta); //This is proportional feedback.
thetaNext += kStep * sign(target-theta); // This moves theta a fixed amount each update. sign(x) = +1 if x >= 0 and -1 if x < 0.
The first solution will cause the rotation to change sharply the further it is from the target. It will also probably oscillate a little bit as it swings past the "zero" point. Bigger values of kProp will yield faster response but also more oscillation. Some tuning will be required.
The second solution will be much easier to control...it just "ticks" the compass needle around each time. You can set kStep to something like 1/4 degree, which gives you a "speed" of rotation of about (1/4 deg/update) * (20 updates/seconds) = 5 degrees per second. This is a bit slow, but you can see the math and change kStep to suit your needs. Note that you may to "band" the "error" value so that no action is taken if the error < kStep (or something like that). This prevents your compass from shifting when the angle is really close to the target. You can change kStep when the error is small so that it "slides" into the ending position (i.e. kStep is smaller when the error is small).
For dealing with Angle Issues (wrap around), I "normalize" the angle so it is always within -Pi/Pi. I don't guarantee this is the perfect way to do it, but it seems to get the job done:
// Takes an angle greater than +/- M_PI and converts it back
// to +/- M_PI. Useful in Box2D where angles continuously
// increase/decrease.
static inline float32 AdjustAngle(float32 angleRads)
{
if(angleRads > M_PI)
{
while(angleRads > M_PI)
{
angleRads -= 2*M_PI;
}
}
else if(angleRads < -M_PI)
{
while(angleRads < -M_PI)
{
angleRads += 2*M_PI;
}
}
return angleRads;
}
By doing it this way, -pi is the angle you reach from going in either direction as you continue to rotate left/right. That is to say, there is not a discontinuity in the number going from say 0 to 359 degrees.
SO PUTTING THIS ALL TOGETHER
static inline float Sign(float value)
{
if(value >= 0)
return 1.0f;
return -1.0f;
}
//#define ROTATION_OPTION_1
//#define ROTATION_OPTION_2
#define ROTATION_OPTION_3
-(void)updateArrow
{
// Calculate the angle to the player
CGPoint toPlayer = ccpSub(self.player.position,self.arrow.position);
// Calculate the angle of this...Note there are some inversions
// and the actual image is rotated 90 degrees so I had to offset it
// a bit.
float angleToPlayerRads = -atan2f(toPlayer.y, toPlayer.x);
angleToPlayerRads = AdjustAngle(angleToPlayerRads);
// This is the angle we "wish" the arrow would be pointing.
float targetAngle = CC_RADIANS_TO_DEGREES(angleToPlayerRads)+90;
float errorAngle = targetAngle-self.arrow.rotation;
CCLOG(#"Error Angle = %f",errorAngle);
#ifdef ROTATION_OPTION_1
// In this option, we just set the angle of the rotated sprite directly.
self.arrow.rotation = CC_RADIANS_TO_DEGREES(angleToPlayerRads)+90;
#endif
#ifdef ROTATION_OPTION_2
// In this option, we apply proportional feedback to the angle
// difference.
const float kProp = 0.05f;
self.arrow.rotation += kProp * (errorAngle);
#endif
#ifdef ROTATION_OPTION_3
// The step to take each update in degrees.
const float kStep = 4.0f;
// NOTE: Without the "if(fabs(...)) check, the angle
// can "dither" around the zero point when it is very close.
if(fabs(errorAngle) > kStep)
{
self.arrow.rotation += Sign(errorAngle)*kStep;
}
#endif
}
I put this code into a demo program I had written for Cocos2d. It shows a character (big box) being chased by some monsters (smaller boxes) and has an arrow in the center that always points towards the character. The updateArrow call is made on a timer tick (the update(dt) function) regularly. The player's position on the screen is set by the user tapping on the screen and the angle is based on the vector from the arrow to the player. In the function, I show all three options for setting the angle of the arrow:
Option 1
Just set it based on where the player is (i.e. just set it).
Option 2
Use proportional feedback to adjust the arrow's angle each time step.
Option 3
Step the angle of the arrow each timestep a little bit if the error angle is more than the step size.
Here is a picture showing roughly what it looks like:
And, all the code is available here on github. Just look in the HelloWorldLayer.m file.
Was this helpful?
I am making an app in which I want to have some thing happen If an image moves over another point. such as
first I have an image moving horizontally across the screen,'
self.ball.center = CGPointMake(self.ball.center.x + self.gravity.x / 8.0 * 200.0, 9);
then when it gets to a certain place another image moves down from that spot.
CGPoint a = CGPointMake(9, 9);
if (CGPointEqualToPoint(ball.center,a)) {
balla.hidden = NO;
self.balla.center = CGPointMake(self.balla.center.x , (self.balla.center.y)- (self.gravity.y / 8.0 * 200.0));
}
the first time it works ok but when I put in the next statement to move another image down from another spot nothing happens.
CGPoint b = CGPointMake(86, 9);
if (CGPointEqualToPoint(ball.center,b)) {
ball2a.hidden = NO;
self.ball2a.center = CGPointMake(self.ball2a.center.x , (self.ball2a.center.y)- (self.gravity.y / 8.0 * 200.0));}
Any ideas as to why this isn't working
If you're moving the ball by adding some floating-point value offset, you might be "skipping over" the point b - you may never hit b, but rather appear slightly before it and then slightly after it.
Rather than testing if you're "equal" to the point, you could be better off comparing the distance between the ball and the point and seeing if it is inside some small radius. A simple euclidean distance could work.
CGFloat euclid_dist(CGPoint a, CGPoint b)
{
return sqrt((b.x-a.x)*(b.x-a.x) + (b.y-a.y)*(b.y-a.y));
}
You could then use this to see if you've "hit" the point:
if (euclid_dist(ball.center, b) < 0.1)
{
// React appropriately
}
In general it's problematic to test for equality between floating point numbers.
Playing around with SKSprites in the IOS SpriteKit, and I basically want to have a sprite randomly move a certain direction for a certain distance, then pick a new random direction and distance.. Simple enough, create a method that generates the random numbers then creates the animation and in the completion block of the animation have it callback the same routine.
THis does work, but it also keeps the animation from moving at the same velocity since the animations are all based on duration.. If the object has to move 100 it moves at 1/2 the speed it moves if the next random tells it to move 200... So how the heck do I have it move with a consistent speed?
#Noah Witherspoon is correct above - use Pythagorus to get a smooth speed:
//the node you want to move
SKNode *node = [self childNodeWithName:#"spaceShipNode"];
//get the distance between the destination position and the node's position
double distance = sqrt(pow((destination.x - node.position.x), 2.0) + pow((destination.y - node.position.y), 2.0));
//calculate your new duration based on the distance
float moveDuration = 0.001*distance;
//move the node
SKAction *move = [SKAction moveTo:CGPointMake(destination.x,destination.y) duration: moveDuration];
[node runAction: move];
Using Swift 2.x I've solved with this little method:
func getDuration(pointA:CGPoint,pointB:CGPoint,speed:CGFloat)->NSTimeInterval {
let xDist = (pointB.x - pointA.x)
let yDist = (pointB.y - pointA.y)
let distance = sqrt((xDist * xDist) + (yDist * yDist));
let duration : NSTimeInterval = NSTimeInterval(distance/speed)
return duration
}
With this method i can use an ivar myShipSpeed and directly call my actions for example :
let move = SKAction.moveTo(dest, duration: getDuration(self.myShip.position,pointB: dest,speed: myShipSpeed))
self.myShip.runAction(move,completion: {
// move action is ended
})
As an extension to #AndyOS's answer, if you're going to move only along one axis (X for example) you can simplify the math by doing this instead:
CGFloat distance = fabs(destination.x - node.position.x);
Im using a technique to control a sprite by rotating left/right and then accelerating forward. I have 2 questions regarding it. (The code it pasted together from different classes due to polymorphism. If it doesn't make sense, let me know. The movement works well and the off screen detection as well.)
When player moves off screen i call the Bounce method. I want the player not to be able to move off screen but to change direction and go back. This works on top and bottom but left and right edge very seldom. Mostly it does a wierd bounce and leaves the screen.
I would like to modify the accelerate algorithm so that i can set a max speed AND a acceleration speed. Atm the TangentalVelocity does both.
float TangentalVelocity = 8f;
//Called when up arrow is down
private void Accelerate()
{
Velocity.X = (float)Math.Cos(Rotation) * TangentalVelocity;
Velocity.Y = (float)Math.Sin(Rotation) * TangentalVelocity;
}
//Called once per update
private void Deccelerate()
{
Velocity.X = Velocity.X -= Friction * Velocity.X;
Velocity.Y = Velocity.Y -= Friction * Velocity.Y;
}
// Called when player hits screen edge
private void Bounce()
{
Rotation = Rotation * -1;
Velocity = Velocity * -1;
SoundManager.Vulture.Play();
}
//screen edge detection
public void CheckForOutOfScreen()
{
//Check if ABOVE screen
if (Position.Y - Origin.Y / 2 < GameEngine.Viewport.Y) { OnExitScreen(); }
else
//Check if BELOW screen
if (Position.Y + Origin.Y / 2 > GameEngine.Viewport.Height) { OnExitScreen(); }
else
//Check if RIGHT of screen
if (this.Position.X + Origin.X / 2 > GameEngine.Viewport.Width) { OnExitScreen(); }
else
//Check if LEFT of screen
if (this.Position.X - Origin.X / 2 < GameEngine.Viewport.X) { OnExitScreen(); }
else
{
if (OnScreen == false)
OnScreen = true;
}
}
virtual public void OnExitScreen()
{
OnScreen = false;
Bounce();
}
Let's see if I understood correctly. First, you rotate your sprite. After that, you accelerate it forward. In that case:
// Called when player hits screen edge
private void Bounce()
{
Rotation = Rotation * -1;
Velocity = Velocity * -1; //I THINK THIS IS THE PROBLEM
SoundManager.Vulture.Play();
}
Let's suposse your sprite has no rotation when it looks up. In that case, if it's looking right it has rotated 90º, and its speed is v = (x, 0), with x > 0. When it goes out of the screen, its rotation becomes -90º and the speed v = (-x, 0). BUT you're pressing the up key and Accelerate method is called so immediately the speed becomes v = (x, 0) again. The sprite goes out of the screen again, changes its velocity to v = (-x, 0), etc. That produces the weird bounce.
I would try doing this:
private void Bounce()
{
Rotation = Rotation * -1;
SoundManager.Vulture.Play();
}
and check if it works also up and bottom. I think it will work. If not, use two different Bounce methods, one for top/bottom and another one for left/right.
Your second question... It's a bit difficult. In Physics, things reach a max speed because air friction force (or another force) is speed-dependent. So if you increase your speed, the force also increases... at the end, that force will balance the other and the speed will be constant. I think the best way to simulate a terminal speed is using this concept. If you want to read more about terminal velocity, take a look on Wikipedia: http://en.wikipedia.org/wiki/Terminal_velocity
private void Accelerate()
{
Acceleration.X = Math.abs(MotorForce - airFriction.X);
Acceleration.Y = Math.abs(MotorForce - airFriction.Y);
if (Acceleration.X < 0)
{
Acceleration.X = 0;
}
if (Acceleration.Y < 0)
{
Acceleration.Y = 0;
}
Velocity.X += (float)Math.Cos(Rotation) * Acceleration.X
Velocity.Y += (float)Math.Sin(Rotation) * Acceleration.Y
airFriction.X = Math.abs(airFrictionConstant * Velocity.X);
airFriction.Y = Math.abs(airFrictionConstant * Velocity.Y);
}
First, we calculate the accelartion using a "MotorForce" and the air friction. The MotorForce is the force we make to move our sprite. The air friction always tries to "eliminate" the movement, so is always postive. We finally take absolute values because the rotation give us the direction of the vector. If the acceleration is lower than 0, that means that the air friction is greater than our MotorForce. It's a friction, so it can't do that: if acceleration < 0, we make it 0 -the air force reached our motor force and the speed becomes constant.
After that, the velocity will increase using the acceleration. Finally, we update the air friction value.
One thing more: you may update also the value of airFriction in the Deccelarate method, even if you don't consider it in that method.
If you have any problem with this, or you don't understand something (sometimes my English is not very good ^^"), say it =)