Make object move in a circle - ios

I'm a beginner at programming, and I've been trying to make an object orbit around another object (or just move in a circle). But I haven't succeeded very well. Any ideas?

You need some constants to specify radius and speed:
const float speed = 100.0f;
const float radius = 50.0f;
you also need some variable to store angle:
float angle;
- (void)updateObject:(NSTimeInterval)dt
{
angle += speed * dt;
angle = fmodf(angle, 360.0f);
float x = cosf(DEGREES_TO_RADIANS(angle)) * radius;
float y = sinf(DEGREES_TO_RADIANS(angle)) * radius;
float newXPosition = _yourSprite.position.x + x;
float newYPosition = _yourSprite.position.y + y;
//Assign the values to your sprite
_yourSprite.position = ...
}

Try connecting two nodes with SKPhysicsJointLimit, with the first node not movable (maybe not dynamic), set the linear damping of the second node to zero and disable gravitation forces on it. It also should not collide with any other object, of course.When the joint is stretched to its maximum and you apply an Impulse vertical to the connection between the two objects, the object should start orbiting around the other one.
I have not tested this one.

Related

(MATH ISSUE) Creating a SPIRAL out of points: How do I change "relative" position to absolute position

Recently I had the idea to make a pendulum out of points using Processing, and with a little learning I solved it easily:
int contador = 0;
int curvatura = 2;
float pendulo;
void setup(){
size(300,300);
}
void draw(){
background(100);
contador = (contador + 1) % 360; //"CONTADOR" GOES FROM 0 TO 359
pendulo = sin(radians(contador))*curvatura; //"PENDULO" EQUALS THE SIN OF CONTADOR, SO IT GOES FROM 1 TO -1 REPEATEDLY, THEN IS MULTIPLIED TO EMPHASIZE OR REDUCE THE CURVATURE OF THE LINE.
tallo(width/2,height/3);
println(pendulo);
}
void tallo (int x, int y){ //THE FUNTION TO DRAW THE DOTTED LINE
pushMatrix();
translate(x,y);
float _y = 0.0;
for(int i = 0; i < 25; i++){ //CREATES THE POINTS SEQUENCE.
ellipse(0,0,5,5);
_y+=5;
rotate(radians(pendulo)); //ROTATE THEM ON EACH ITERATION, THIS MAKES THE SPIRAL.
}
popMatrix();
}
So, in a brief, what I did was a function that changed every point position with the rotate fuction, and then I just had to draw the ellipses in the origin coordinates as that is the real thing that changes position and creates the pendulum ilussion.
[capture example, I just need 2 more points if you are so gentile :)]
[capture example]
[capture example]
Everything was OK that far. The problem appeared when I tried to replace the ellipses for a path made of vertices. The problem is obvious: the path is never (visually) made because all vertices would be 0,0 as they move along with the zero coordinates.
So, in order to make the path possible, I need the absolute values for each vertex; and there's the question: How do I get them?
What I know I have to do is to remove the transform functions, create the variables for the X and Y position and update them inside the for, but then what? That's why I cleared this is a maths issue, which operation I have to add in the X and Y variables in order to make the path and its curvature possible?
void tallo (int x, int y){
pushMatrix();
translate(x,y);
//NOW WE START WITH THE CHANGES. LET'S DECLARE THE VARIABLES FOR THE COORDINATES
float _x = 0.0;
float _y = 0.0;
beginShape();
for(int i = 0; i < 25; i++){ //CREATES THE DOTS.
vertex(_x,_y); //CHANGING TO VERTICES AND CALLING THE NEW VARIABLES, OK.
//rotate(radians(pendulo)); <--- HERE IS MY PROBLEM. HOW DO I CONVERT THIS INTO X AND Y COORDINATES?
//_x = _x + ????;
_y = _y + 5 /* + ???? */;
}
endShape();
popMatrix();
}
We need to have in mind that pendulo's x and y values changes in each iteration of the for, it doesn't has to add the same quantity each time. The addition must be progressive. Otherwise, we would see a straight line rotating instead of a curve accentuating its curvature (if you increase curvatura's value to a number greater than 20, you will notice the spiral)
So, rotating the coordinates was a great solution to it, now it's kind of a muddle to think the mathematical solution to the x and y coordinates for the spiral, my secondary's knowledges aren't enough. I know I have to create another variable inside the for in order to do this progression, but what operation should it have?
I would be really glad to know, maths
You could use simple trigonometry. You know the angle and the hypotenuse, so you use cos to get the relative x position, and sin to the y. The position would be relative to the central point.
But before i explain in detail and draw some explanations, let me propose another solution: PVectors
void setup() {
size(400,400);
frameRate(60);
center = new PVector(width/2, height/3); //defined here because width and height only are set after size()
}
void draw() {
background(255);
fill(0);
stroke(0);
angle = arc_magn*sin( (float) frameCount/60 );
draw_pendulum( center );
}
PVector center;
float angle = 0;
float arc_magn = HALF_PI;
float wire_length = 150;
float rotation_angle = PI/20 /60 ; //we divide it by 60 so the first part is the rotation in one second
void draw_pendulum(PVector origin){
PVector temp_vect = PVector.fromAngle( angle + HALF_PI);
temp_vect.setMag(wire_length);
PVector final_pos = new PVector(origin.x+temp_vect.x, origin.y+temp_vect.y );
ellipse( final_pos.x, final_pos.y, 40, 40);
line(origin.x, origin.y, final_pos.x, final_pos.y);
}
You use PVector class static method fromAngle( float angle ) that returns a unity vector of the given angle, then use .setMag() to define it's length.
Those PVector methods will take care of the trigonometry for you.
If you still want to know the math behind it, i can make another example.

SpriteKit move rotated physicsBody with applyImpulse

I want to move a physicsBody with the applyImpulse method in a direction based on the physicsBody rotation.
Foe example, the physicsBody is a square in shape, I call a "move" which will apply an impulse to make it move up vertically. I then call a method to rotate the physicsBody 45 degrees right. If I call the "move" method again, the physicsBody will move diagonally right and up.
I suggest that you follow Sprite Kit’s coordinate and rotation conventions. Specifically, your sprite image should be facing right at zero degrees (the default value), and a positive value is a counter-clockwise rotation. That said, here's one way to apply an impulse in the direction a sprite is facing:
// Specify the force to apply to the SKPhysicsBody
CGFloat r = 5;
// Create a vector in the direction the sprite is facing
CGFloat dx = r * cos (sprite.zRotation);
CGFloat dy = r * sin (sprite.zRotation);
// Apply impulse to physics body
[sprite.physicsBody applyImpulse:CGVectorMake(dx,dy)];
UPDATED:
Fixed with the below thanks to #0x141E
-(void)characterJump {
CGFloat radianFactor = 0.0174532925;
CGFloat rotationInDegrees = _body.zRotation / radianFactor;
CGFloat newRotationDegrees = rotationInDegrees + 90;
CGFloat newRotationRadians = newRotationDegrees * radianFactor;
CGFloat r = 500;
CGFloat dx = r * cos(newRotationRadians);
CGFloat dy = r * sin(newRotationRadians);
[_body.physicsBody applyImpulse:CGVectorMake(dx, dy)];
}

How to determine closest CGPoint with an angle and another CGPoint

I calculate angle between two CGPoints :
//calculate radian and degree
CGPoint diff = ccpSub(center, location);//return ccp(v1.x - v2.x, v1.y - v2.y);
float rads = atan2f( diff.y, diff.x);
float degs = -CC_RADIANS_TO_DEGREES(rads);
NSLog(#"Rad %.2f Degs %.2f",rads,degs);
Now In another function where I have a pre known CGPoint and the degree of above function, I want to calculate closest point that satisfies the degree.
I was thinking about maybe below code would help me but in below code start point and rotation point is known, in my situation I only know start point.
-(void) rotateAroundPoint:(CGPoint)rotationPoint angle:(CGFloat)angle {
CGFloat x = cos(CC_DEGREES_TO_RADIANS(-angle)) * (self.position.x-rotationPoint.x) - sin(CC_DEGREES_TO_RADIANS(-angle)) * (self.position.y-rotationPoint.y) + rotationPoint.x;
CGFloat y = sin(CC_DEGREES_TO_RADIANS(-angle)) * (self.position.x-rotationPoint.x) + cos(CC_DEGREES_TO_RADIANS(-angle)) * (self.position.y-rotationPoint.y) + rotationPoint.y;
Lets say I have a point 800,600 and I have a degree of 70, how can I calculate closest point with that point and that degree?
EDIT:::
Normally in my game sprites are moved with a button therefore all rotation,movement,speed etc are handled when button pressed [sprite moveToPreGivenPostion:CGPoint]
But now a compass is added and when user choose an angle on the compass I need to move the sprite in the direction of degree on compass, since [sprite moveToPreGivenPostion:CGPoint] already handles rotation and other stuff I just want to determine that what CGPoint should I send to moveToPreGivenPostion function.
As #trumpetlicks said you cant find the closest point like that, but I guess I understood what you want and that function -(void) rotateAroundPoint:(CGPoint)rotationPoint angle:(CGFloat)angle you are trying to use is perfectly fine to achieve what you want.
all you need to do is choose float radius.
you know your current point and lets say your radius is 1, basically you can calculate your previous point without a degree, assuming 0 degrees is left of your point and lets say your point is 200,200 with 1 radius 0 degree your previous point automatically becomes 199,200.
So now you have a reference point so now calculate the point you want to move your sprite:
//choose a feasable radius
float radius = 0.5;
//position_ is your preknown position as you said
//find a the point to roate
//position_.x-radius is always 0 degrees of your current point
CGFloat x = cos(rads) * ((position_.x-radius)-position_.x) - sin(rads) * ((position_.y)-position_.y) + position_.x;
CGFloat y = sin(rads) * ((position_.x-radius)-position_.x) + cos(rads) * ((position_.y)-position_.y) + position_.y;
//get the new point
CGPoint newLocation = ccp(x, y);

How to move 2 xna sprites away from eachother dynamically?

I have two items, lets call them Obj1 and Obj2... Both have a current position pos1 and pos2.. Moreover they have current velocity vectors speed1 and speed2 ... How can I make sure that if their distances are getting closer (with checking current and NEXT distance), they will move farther away from eachother ?
I have a signed angle function that gives me the signed angle between 2 vectors.. How can I utilize it to check how much should I rotate the speed1 and speed2 to move those sprites from eachother ?
public float signedAngle(Vector2 v1, Vector2 v2)
{
float perpDot = v1.X * v2.Y - v1.Y * v2.X;
return (float)Math.Atan2(perpDot, Vector2.Dot(v1, v2));
}
I check the NEXT and CURRENT distances like that :
float currentDistance = Vector2.Distance(s1.position, s2.position);
Vector2 obj2_nextpos = s2.position + s2.speed + s2.drag;
Vector2 obj1_nextpos = s1.position + s1.speed + s1.drag;
Vector2 s2us = s2.speed;
s2us.Normalize();
Vector2 s1us = s1.speed;
s1us.Normalize();
float nextDistance = Vector2.Distance(obj1_nextpos , obj2_nextpos );
Then depending whether they are getting bigger or smaller I want to move them away (either by increasing their current speed at the same direction or MAKING THEM FURTHER WHICH I FAIL)...
if (nextDistance < currentDistance )
{
float angle = MathHelper.ToRadians(180)- signedAngle(s1us, s2us);
s1.speed += Vector2.Transform(s1us, Matrix.CreateRotationZ(angle)) * esc;
s2.speed += Vector2.Transform(s2us, Matrix.CreateRotationZ(angle)) * esc;
}
Any ideas ?
if objects A and B are getting closer, one of the object components (X or Y) is opposite.
in this case Bx is opposite to Ax, so only have to add Ax to the velocity vector of object B, and Bx to velocity vector of object A
If I understood correctly, this is the situation and you want to obtain the two green vectors.
The red vector is easy to get: redVect = pos1 - pos2. redVect and greenVect2 will point to the same direction, so the only step you have is to scale it so its length will match speed2's one: finalGreenVect2 = greenvect2.Normalize() * speed2.Length (although I'm not actually sure about this formula). greenVect1 = -redVect so finalGreenVect1 = greenVect1.Normalize() * speed1.Length. Then speed1 = finalGreenVect1 and speed2 = finalGreenVect2. This approach will give you instant turn, if you prefer a smooth turn you want to rotate the speed vector by:
angle = signedAngle(speed) + (signedAngle(greenVect) - signedAngle(speed)) * 0.5f;
The o.5f is the rotation speed, adjust it to any value you need. I'm afraid that you have to create a rotation matrix then Transform() the speed vector with this matrix.
Hope this helps ;)

Algorithm for creating a circular path around a center mass?

I am attempting to simply make objects orbit around a center point, e.g.
The green and blue objects represent objects which should keep their distance to the center point, while rotating, based on an angle which I pass into method.
I have attempted to create a function, in objective-c, but it doesn't work right without a static number. e.g. (It rotates around the center, but not from the true starting point or distance from the object.)
-(void) rotateGear: (UIImageView*) view heading:(int)heading
{
// int distanceX = 160 - view.frame.origin.x;
// int distanceY = 240 - view.frame.origin.y;
float x = 160 - view.image.size.width / 2 + (50 * cos(heading * (M_PI / 180)));
float y = 240 - view.image.size.height / 2 + (50 * sin(heading * (M_PI / 180)));
view.frame = CGRectMake(x, y, view.image.size.width, view.image.size.height);
}
My magic numbers 160, and 240 are the center of the canvas in which I'm drawing the images onto. 50 is a static number (and the problem), which allows the function to work partially correctly -- without maintaining the starting poisition of the object or correct distance. I don't know what to put here unfortunately.
heading is a parameter that passes in a degree, from 0 to 359. It is calculated by a timer and increments outside of this class.
Essentially what I would like to be able to drop any image onto my canvas, and based on the starting point of the image, it would rotate around the center of my circle. This means, if I were to drop an image at Point (10,10), the distance to the center of the circle would persist, using (10,10) as a starting point. The object would rotate 360 degrees around the center, and reach it's original starting point.
The expected result would be to pass for instance (10,10) into the method, based off of zero degrees, and get back out, (15,25) (not real) at 5 degrees.
I know this is very simple (and this problem description is entirely overkill), but I'm going cross eyed trying to figure out where I'm hosing things up. I don't care about what language examples you use, if any. I'll be able to decipher your meanings.
Failure Update
I've gotten farther, but I still cannot get the right calculation. My new code looks like the following:
heading is set to 1 degree.
-(void) rotateGear: (UIImageView*) view heading:(int)heading
{
float y1 = view.frame.origin.y + (view.frame.size.height/2); // 152
float x1 = view.frame.origin.x + (view.frame.size.width/2); // 140.5
float radius = sqrtf(powf(160 - x1 ,2.0f) + powf(240 - y1, 2.0f)); // 90.13
// I know that I need to calculate 90.13 pixels from my center, at 1 degree.
float x = 160 + radius * (cos(heading * (M_PI / 180.0f))); // 250.12
float y = 240 + radius * (sin(heading * (M_PI / 180.0f))); // 241.57
// The numbers are very skewed.
view.frame = CGRectMake(x, y, view.image.size.width, view.image.size.height);
}
I'm getting results that are no where close to where the point should be. The problem is with the assignment of x and y. Where am I going wrong?
You can find the distance of the point from the centre pretty easily:
radius = sqrt((160 - x)^2 + (240 - y)^2)
where (x, y) is the initial position of the centre of your object. Then just replace 50 by the radius.
http://en.wikipedia.org/wiki/Pythagorean_theorem
You can then figure out the initial angle using trigonometry (tan = opposite / adjacent, so draw a right-angled triangle using the centre mass and the centre of your orbiting object to visualize this):
angle = arctan((y - 240) / (x - 160))
if x > 160, or:
angle = arctan((y - 240) / (x - 160)) + 180
if x < 160
http://en.wikipedia.org/wiki/Inverse_trigonometric_functions
Edit: bear in mind I don't actually know any Objective-C but this is basically what I think you should do (you should be able to translate this to correct Obj-C pretty easily, this is just for demonstration):
// Your object gets created here somewhere
float x1 = view.frame.origin.x + (view.frame.size.width/2); // 140.5
float y1 = view.frame.origin.y + (view.frame.size.height/2); // 152
float radius = sqrtf(powf(160 - x1 ,2.0f) + powf(240 - y1, 2.0f)); // 90.13
// Calculate the initial angle here, as per the first part of my answer
float initialAngle = atan((y1 - 240) / (x1 - 160)) * 180.0f / M_PI;
if(x1 < 160)
initialAngle += 180;
// Calculate the adjustment we need to add to heading
int adjustment = (int)(initialAngle - heading);
So we only execute the code above once (when the object gets created). We need to remember radius and adjustment for later. Then we alter rotateGear to take an angle and a radius as inputs instead of heading (this is much more flexible anyway):
-(void) rotateGear: (UIImageView*) view radius:(float)radius angle:(int)angle
{
float x = 160 + radius * (cos(angle * (M_PI / 180.0f)));
float y = 240 + radius * (sin(angle * (M_PI / 180.0f)));
// The numbers are very skewed.
view.frame = CGRectMake(x, y, view.image.size.width, view.image.size.height);
}
And each time we want to update the position we make a call like this:
[objectName rotateGear radius:radius angle:(adjustment + heading)];
Btw, once you manage to get this working, I'd strongly recommend converting all your angles so you're using radians all the way through, it makes it much neater/easier to follow!
The formula for x and y coordinates of a point on a circle, based on radians, radius, and center point:
x = cos(angle) * radius + center_x
y = sin(angle) * radius + center_y
You can find the radius with HappyPixel's formula.
Once you figure out the radius and the center point, you can simply vary the angle to get all the points on the circle that you'd want.
If I understand correctly, you want to do InitObject(x,y). followed by UpdateObject(angle) where angle sweeps from 0 to 360. (But use radians instead of degrees for the math)
So you need to track the angle and radius for each object.:
InitObject(x,y)
relative_x = x-center.x
relative_y = y-center.y
object.radius = sqrt((relative_x)^2, (relative_y)^2)
object.initial_angle = atan(relative_y,relative_x);
And
UpdateObject(angle)
newangle = (object.initial_angle + angle) % (2*PI )
object.x = cos(newangle) * object.radius + center.x
object.y = sin(newangle) * object.radius + center.y
dx=dropx-centerx; //target-source
dy=-(dropy-centery); //minus = invert screen coords to cartesian coords
radius=sqrt(dy*dy+dx*dx); //faster if your compiler optimizer is bad
if dx=0 then dx=0.000001; //hackpatchfudgenudge*
angle=atan(dy/dx); //set this as start angle for the angle-incrementer
Then go with the code you have and you'll be fine. You seem to be calculating radius from current position each time though? This, like the angle, should only be done once, when the object is dropped, or else the radius might not be constant.
*instead of handling 3 special cases for dx=0, if you need < 1/100 degree precision for the start angle go with those instead, google Polar Arctan.

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