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)];
}
Related
I have an app with a color wheel and I'm trying to pick a random color within the color wheel. However, I'm having problems verifying that the random point falls within the color wheel.
Here's the code as it currently is:
CGPoint randomPoint = CGPointMake(arc4random() % (int)colorWheel.bounds.size.width, arc4random() % (int)colorWheel.bounds.size.height);
UIColor *randomColor = [self colorOfPoint:randomPoint];
CGPoint pointInView = [colorWheel convertPoint:randomPoint fromView:colorWheel.window];
if (CGRectContainsPoint(colorWheel.bounds, pointInView)) {
NSLog(#"%#", randomColor);
}
else {
NSLog(#"out of bounds");
}
A couple of other methods of verifying the point that I've tried with no luck:
if (CGRectContainsPoint(colorWheel.frame, randomPoint)) {
NSLog(#"%#", randomColor);
}
if ([colorWheel pointInside:[self.view convertPoint:randomPoint toView: colorWheel] withEvent: nil]) {
NSLog(#"%#", randomColor);
}
Sometimes it'll output "out of bounds", and sometimes it'll just output that the color is white (the background around the color wheel is currently white but there's no white in the color wheel image).
The color wheel image is a circle, so I'm not sure if that's throwing off the test, although it seems like white pops up way too frequently for it to just be a transparent square outline around the image giving a white color.
If you want to generate a random point in a circle, you would do better to pick your point in polar coordinates and then convert it to Cartesian.
The polar coordinate space uses two dimesions, radius and angle. Radius is just the distance from the center, and angle usually starts at "due east" for 0, and goes around counter-clockwise up to 2π (that's in radians, 360˚ of course in degrees).
Presumably your wheel is divided into simple wedges, so the radius actually doesn't matter; you just need to pick a random angle.
uint32_t angle = arc4random_uniform(360);
// Radius will just be halfway from the center to the edge.
// This assumes the circle is exactly enclosed, i.e., diameter == width
CGFloat radius = colorWheel.bounds.size.width / 4;
This function will give you a Cartesian point from your polar coordinates. Wikipedia explains the simple math if you're interested.
/** Convert the polar point (radius, theta) to a Cartesian (x,y). */
CGPoint poltocar(CGFloat radius, CGFloat theta)
{
return (CGPoint){radius * cos(theta), radius * sin(theta)};
}
The function uses radians for theta, because sin() and cos() do, so change the angle to radians, and then you can convert:
CGFloat theta = (angle * M_PI) / 180.0
CGPoint randomPoint = poltocar(radius, theta);
One last step: this circle has its origin at the same place as the view, that is, in the corner, so you need to translate the point to use the center as the origin.
CGPoint addPoints(CGPoint lhs, CGPoint rhs)
{
return (CGPoint){lhs.x + rhs.x, lhs.y, rhs.y};
}
CGPoint offset = (CGPoint){colorWheel.bounds.size.width / 2,
colorWheel.bounds.size.height / 2};
randomPoint = addPoints(randomPoint, offset);
And your new randomPoint will always be within the circle.
I agree with #JoshCaswell's approach, but FYI, the reason the OP code is not working is that the test for inside a circle is incorrect.
The coordinate conversion is unnecessary, and the test against a rectangle is sure to be wrong. Instead, work out how far the random point is from the center and compare that with the radius.
CGFloat centerX = colorWheel.bounds.size.width / 2.0;
CGFloat centerY = colorWheel.bounds.size.height / 2.0;
CGFloat distanceX = centerX - randomPoint.x;
CGFloat distanceY = centerY - randomPoint.y;
CGFloat distance = distanceX*distanceX + distanceY*distanceY;
CGFloat radius = colorWheel.bounds.size.width / 2.0; // just a guess
CGFloat r2 = radius*radius;
// this compares the square of the distance with r^2, to save a sqrt operation
BOOL isInCircle = distance < r2;
I want to give Force to my SKSpriteNode at specific angle.
So, How to treat my CGVector for give force at specific angle?
I had searched for it but unfortunately not getting any good way.
What i wants to achieve :
My SKSpriteNode moving towards the screen. There are buttons on top like 30,45,60.
So if user press button(i.e. that Button contain "30") then i had to move my SKSpriteNode to 30 degree with same speed.
Please help me towards it if any of you can help me regarding this.
First, you will need to convert the angle in degrees to radians by multiplying it by pi / 180
CGFloat angleInRadians = angleInDegrees * M_PI / 180;
You can then determine the vector components in that direction by
CGFloat dx = cosf(angleInRadians);
CGFloat dy = sinf(angleInRadians);
and finally apply a force to the sprite with
[sprite.physicsBody applyForce:CGVectorMake(dx*scale, dy*scale)];
where scale determines how much force is applied.
Optionally, you can rotate the sprite to face in the same direction as its motion by
sprite.zRotation = angleInRadians + offset;
where offset is the difference in angle, in radians, between your sprite's image and zero degrees. For example, if your sprite is facing up when zRotation is zero, offset should be -M_PI_2.
In my iOS application I have a texture applied to a sphere rendered in OpenGLES1. The sphere can be rotated by the user. How can I track where a given point on the texture is in 2D space at any given time?
For example, given point (200, 200) on a texture that's 1000px x 1000px, I'd like to place a UIButton on top of my OpenGL view that tracks the point as the sphere is manipulated.
What's the best way to do this?
On my first attempt, I tried to use a color-picking technique where I have a separate sphere in an off-screen framebuffer that uses a black texture with a red square at point (200, 200). Then, I used glReadPixels() to track the position of the red square and I moved my button accordingly. Unfortunately, grabbing all the pixel data and iterating it 60 times a second just isn't possible for obvious performance reasons. I tried a number of ways to optimize this hack (eg: iterating only the red pixels, iterating every 4th red pixel, etc), but it just didn't prove to be reliable.
I'm an OpenGL noob, so I'd appreciate any guidance. Is there a better solution? Thanks!
I think it's easier to keep track of where your ball is instead of searching for it with pixels. Then just have a couple of functions to translate your ball's coordinates to your view's coordinates (and back), then set your subview's center to the translated coordinates.
CGPoint translatePointFromGLCoordinatesToUIView(CGPoint coordinates, UIView *myGLView){
//if your drawing coordinates were between (horizontal {-1.0 -> 1.0} vertical {-1 -> 1})
CGFloat leftMostGLCoord = -1;
CGFloat rightMostGLCoord = 1;
CGFloat bottomMostGLCoord = -1;
CGFloat topMostGLCoord = 1;
CGPoint scale;
scale.x = (rightMostGLCoord - leftMostGLCoord) / myGLView.bounds.size.width;
scale.y = (topMostGLCoord - bottomMostGLCoord) / myGLView.bounds.size.height;
coordinates.x -= leftMostGLCoord;
coordinates.y -= bottomMostGLCoord;
CGPoint translatedPoint;
translatedPoint.x = coordinates.x / scale.x;
translatedPoint.y =coordinates.y / scale.y;
//flip y for iOS coordinates
translatedPoint.y = myGLView.bounds.size.height - translatedPoint.y;
return translatedPoint;
}
CGPoint translatePointFromUIViewToGLCoordinates(CGPoint pointInView, UIView *myGLView){
//if your drawing coordinates were between (horizontal {-1.0 -> 1.0} vertical {-1 -> 1})
CGFloat leftMostGLCoord = -1;
CGFloat rightMostGLCoord = 1;
CGFloat bottomMostGLCoord = -1;
CGFloat topMostGLCoord = 1;
CGPoint scale;
scale.x = (rightMostGLCoord - leftMostGLCoord) / myGLView.bounds.size.width;
scale.y = (topMostGLCoord - bottomMostGLCoord) / myGLView.bounds.size.height;
//flip y for iOS coordinates
pointInView.y = myGLView.bounds.size.height - pointInView.y;
CGPoint translatedPoint;
translatedPoint.x = leftMostGLCoord + (pointInView.x * scale.x);
translatedPoint.y = bottomMostGLCoord + (pointInView.y * scale.y);
return translatedPoint;
}
In my app I choose to use the iOS coordinate system for my drawing too. I just apply a projection matrix to my whole glkView the reconciles the coordinate system.
static GLKMatrix4 GLKMatrix4MakeIOSCoordsWithSize(CGSize screenSize){
GLKMatrix4 matrix4 = GLKMatrix4MakeScale(
2.0 / screenSize.width,
-2.0 / screenSize.height,
1.0);
matrix4 = GLKMatrix4Translate(matrix4,-screenSize.width / 2.0, -screenSize.height / 2.0, 0);
return matrix4;
}
This way you don't have to translate anything.
I am trying to use applyImpulse to make a sprite jump to a specific height. In the example code below, the dynamic black circle jumps to the same height as the static red circle, but it only works with a kludge.
If my physics is right, the required initial vertical momentum to launch a projectile to height Y is given by mass * sqrt(2 * gravity * Y). Yet this formula results in the black circle moving very little.
Through trial and error, I have discovered that I can make the red circle jump more or less accurately by multiplying the vertical component of the impulse vector by 12.3, as illustrated in the code below.
This seems completely arbitrary and is driving me crazy. I am obviously doing something wrong. What's the right way to do this?
Here's what I think is the relevant bit of code:
let dy = mass * sqrt(
2 * -self.physicsWorld.gravity.dy
* (fixedCircle.position.y-jumpingCircle.position.y))
* 12.3
jumpingCircle.physicsBody?.applyImpulse(CGVectorMake(0, CGFloat(dy)))
Here's the GameScene.swift class in its entirety, should you wish to copy and paste...
import SpriteKit
class GameScene: SKScene {
var jumpingCircle = SKShapeNode()
var fixedCircle = SKShapeNode()
override func didMoveToView(view: SKView) {
self.scaleMode = .AspectFit
// Create an exterior physical boundary
self.physicsBody = SKPhysicsBody(edgeLoopFromRect:self.frame)
self.physicsWorld.gravity = CGVectorMake(0, -5);
// Create the jumping circle
jumpingCircle = SKShapeNode(circleOfRadius: 50)
jumpingCircle.position = CGPoint(x: 100,y: 0)
jumpingCircle.strokeColor = .blackColor()
jumpingCircle.physicsBody = SKPhysicsBody(circleOfRadius: 50)
jumpingCircle.physicsBody?.linearDamping = 0.0
self.addChild(jumpingCircle)
// Create the fixed circle
fixedCircle = SKShapeNode(circleOfRadius: 50)
fixedCircle.position = CGPoint(x: 100,y: 384)
fixedCircle.strokeColor = .redColor()
self.addChild(fixedCircle)
}
override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent) {
// to reach certain height, initial y velocity should by sqrt(2 * gravity * Y)
// momentum required to reach this velocity is mass * velocity
// therefore, vertical impulse should be given by mass * sqrt(2 * gravity * Y)
if let mass = jumpingCircle.physicsBody?.mass{
// calculate vertical impulse
// this formula "should work" but does not
// let dy = mass * sqrt(2 * -self.physicsWorld.gravity.dy * (fixedCircle.position.y-jumpingCircle.position.y))
// this formula "works", but has the arbitrary multiplier
let dy = mass * sqrt(2 * -self.physicsWorld.gravity.dy * (fixedCircle.position.y-jumpingCircle.position.y)) * 12.3
// apply the Impulse
jumpingCircle.physicsBody?.applyImpulse(CGVectorMake(0, CGFloat(dy)))
}
}
}
Figured it out.
SpriteKit apparently has an undocumented pixel-to-"meter" ratio of 150.
I discovered this when I realized the mass SpriteKit was automatically calculating for my circles was not 50*pi*r^2 as it should be. I worked backward from mass to calculate the radius SpriteKit was using, and it was 7500, which happens to be 50*150.
And 12.3? It just happens to be (approximately) the square root of 150.
So to make these physics simulations work, you have to consider this ratio. I'm calling it "pixel to unit" (PTU) because it has nothing to do with meters in spite of Apple's insistence that SpriteKit uses SI units. But because it's undocumented it seems possible to change, so I'm kicking off my simulation using the following line of code to determine the true PTU:
let ptu = 1.0 / sqrt(SKPhysicsBody(rectangleOfSize: CGSize(width:1,height:1)).mass)
This is an expensive operation, so it should only be called once. I'm calling it when setting up the initial Scene.
My impulse calculation is now as follows:
let dy = mass * sqrt(2
* -self.physicsWorld.gravity.dy
* (fixedCircle.position.y-jumpingCircle.position.y
* ptu))
And now the black circle jumps to perfect alignment with the red circle and I can go back to sleeping at night.
Instead of applyImpulse use velocity. Velocity will be more specific.
jumpingCircle.physicsBody?.velocity = CGVectorMake(jumpingCircle.physicsBody.velocity.dx, 300.0f);
Code not tested.
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.