At the beginning I have declared the nodes.
//Declaration of the ground nodes.
var groundImage: SKSpriteNode = SKSpriteNode()
var groundImage2: SKSpriteNode = SKSpriteNode()
In the viewDidLoad I have:
//Creates an instance of both sprites that are of the same image that are to be lined up against each other in the x axis creating the illution of continuity.
groundImage = SKSpriteNode(imageNamed: "Ground.png")
groundImage2 = SKSpriteNode(imageNamed: "Ground.png")
//Specifies the Z position of the images.
groundImage.zPosition = 3
groundImage2.zPosition = 3
//Scales the images to the correct size of the screen.
groundImage.size.width = self.frame.width
groundImage.size.height = self.groundImage.size.height / 2
groundImage2.size.width = self.frame.width
groundImage2.size.height = self.groundImage2.size.height / 2
//Specicies the x position of the images. By offsetting the second you create the illution of a long, continuous image.
groundImage.position.x = view.bounds.size.width * 0.5
groundImage2.position.x = view.bounds.size.width * 1.5
//Specifies the y postion of the images, obviously these are the same as they are not to be offset at any time.
groundImage.position.y = (view.bounds.size.height - view.bounds.size.height) + self.groundImage.size.height / 2
groundImage2.position.y = (view.bounds.size.height - view.bounds.size.height) + self.groundImage2.size.height / 2
//Not sure what this does yet.
groundImage.texture?.filteringMode = SKTextureFilteringMode.Nearest
groundImage2.texture?.filteringMode = SKTextureFilteringMode.Nearest
//Adds instances of the sprites to the scene.
self.addChild(groundImage)
self.addChild(groundImage2)
In the update method I have:
//This is how the image is moved relative the number specified. The number in the variable is how many pixels the frame is being moved each frame refresh.
groundImage.position.x -= gameSpeed
groundImage2.position.x -= gameSpeed
if (groundImage.position.x <= -self.view!.bounds.size.width / 2)
{
groundImage.position.x = self.view!.bounds.size.width * 1.5 // - 2
}
if (groundImage2.position.x <= -self.view!.bounds.size.width / 2)
{
groundImage2.position.x = self.view!.bounds.size.width * 1.5 // - 2
}
Any yet there is a slight gap between the two images when they are looping. This gap increases as I increase the speed they are looped at using a game speed variable.
Can anyone explain to me what I have done wrong please?
I have checked the images themselves are not causing the issue.
Thanks,
Steven
The gap is probably because the update method called about 60 times in a second (defaults is 60 fps if I am not wrong),
you should use SKAction to simply flip your images,
it will be much more efficient. Here is your starting point:
https://developer.apple.com/library/ios/documentation/GraphicsAnimation/Conceptual/SpriteKit_PG/AddingActionstoSprites/AddingActionstoSprites.html
I want to randomly generate the position for a sprite. I use the arc4random() method to get a range from 1 to 8.
var randomFactor = arc4random_uniform(8) + 1
sprite.position = CGPointMake(self.frame.width/8 * randomFactor, self.frame.height)
An error pops up telling me "UIInt32 is not convertible to UIInt8".
Is there a way to get around this or design the code differently to make it work? Like a solution where the random method isn't a UIInt32 but a UIInt8.
Thanks in advance.
You should convert 'randomFactor' to a CGFloat:
var randomFactor = arc4random_uniform(8) + 1
var x = self.frame.width / 8 * CGFloat(randomFactor)
var y = self.frame.height
var position = CGPointMake(x, y)
As my tile says that I want to get random number for origin (X-Axis & y-Axis) so in my whole screen in iPad landscape I have 1 rectangle, I want to get random number for origin which out of this rectangle, so obiously I want to get random number for X-Axis between max and min and same as for Y-Axis.
I tried with following answers but not helpful for me.
Generate Random Numbers Between Two Numbers in Objective-C
Generate a random float between 0 and 1
Generate random number in range in iOS?
For more clear see below image
In above image I just want to find random number (for origin) of GREEN screen. How can I achieve it ?
Edited
I had tried.
int randNum = rand() % ([max intValue] - [min intValue]) + [min intValue];
Same for both X-Axis & y-Axis.
If the blue exclusion rectangle is not "too large" compared to the green screen rectangle
then the easiest solution is to
create a random point inside the green rectangle,
check if the point lies inside the blue rectangle, and
repeat the process if necessary.
That would look like:
CGRect greenRect = ...;
CGRect blueRect = ...;
CGPoint p;
do {
p = CGPointMake(greenRect.origin.x + arc4random_uniform(greenRect.size.width),
greenRect.origin.y + arc4random_uniform(greenRect.size.height));
} while (CGRectContainsPoint(blueRect, p));
If I remember correctly, the expected number of iterations is G/(G - B), where G is
the area of the green rectangle and B is the area of the blue rectangle.
What if you first determined x within the green rectangle like this:
int randomX = arc4random()%greenRectangle.frame.size.width;
int randomY; // we'll do y later
Then check if this is inside the blue rectangle:
if(randomX < blueRectangle.frame.origin.x && randomX > (blueRectangle.frame.origin.x + blueRectangle.frame.size.width))
{
//in this case we are outside the rectangle with the x component
//so can randomly generate any y like this:
randomY = arc4random()%greenRectangle.frame.size.height;
}
//And if randomX is in the blue rectangle then we can use the space either before or after it:
else
{
//randomly decide if you are going to use the range to the left of blue rectangle or to the right
BOOL shouldPickTopRange = arc4random()%1;
if(shouldPickTopRange)
{
//in this case y can be any point before the start of blue rectangle
randomY = arc4random()%blueRectangle.frame.origin.y;
}
else
{
//in this case y can be any point after the blue rectangle
int minY = blueRectangle.frame.origin.y + blueRectangle.frame.size.height;
int maxY = greenRectangle.frame.size.height;
randomY = arc4random()%(maxY - minY + 1) + minY;
}
}
Then your random point would be:
CGPoint randomPoint = CGPointMake(randomX, randomY);
The only thing missing above is to check if your blue rectangle sits at y = 0 or at the very bottom of green rectangle.
[Apologies I did this with OS X, translation is straightforward]
A non-iterative solution:
- (NSPoint) randomPointIn:(NSRect)greenRect excluding:(NSRect)blueRect
{
// random point on green x-axis
int x = arc4random_uniform(NSWidth(greenRect)) + NSMinX(greenRect);
if (x < NSMinX(blueRect) || x > NSMaxX(blueRect))
{
// to the left or right of the blue, full height available
int y = arc4random_uniform(NSHeight(greenRect)) + NSMinY(greenRect);
return NSMakePoint(x, y);
}
else
{
// within the x-range of the blue, avoid it
int y = arc4random_uniform(NSHeight(greenRect) - NSHeight(blueRect)) + NSMinY(greenRect);
if (y >= NSMinY(blueRect))
{
// not below the blue, step over it
y += NSHeight(blueRect);
}
return NSMakePoint(x, y);
}
}
This picks a random x-coord in the range of green. If that point is outside the range of blue it picks a random y-coord in the range of green; otherwise it reduces the y range by the height of blue, produces a random point, and then increases it if required to avoid blue.
There are other solutions based on picking a uniform random point in the available area (green - blue) and then adjusting, but the complexity isn't worth it I think (I haven't done the stats).
Addendum
OK folk seem concerned over uniformity, so here is the algorithm mentioned in my last paragraph. We're picking an "point" with integer coords so the number of points to pick from is the green area minus the blue area. Pick a point randomly in this range. Now place it into one of the rectangles below, left, right or above the blue:
// convenience
int RectArea(NSRect r) { return (int)NSWidth(r) * (int)NSHeight(r); }
- (NSPoint) randomPointIn:(NSRect)greenRect excluding:(NSRect)blueRect
{
// not we are using "points" with integer coords so the
// bottom left point is 0,0 and the top right (width-1, height-1)
// you can adjust this to suit
// the number of points to pick from is the diff of the areas
int availableArea = RectArea(greenRect) - RectArea(blueRect);
int pointNumber = arc4random_uniform(availableArea);
// now "just" locate pointNumber into the available space
// we consider four rectangles, one each full width above and below the blue
// and one each to the left and right of the blue
int belowArea = NSWidth(greenRect) * (NSMinY(blueRect) - NSMinY(greenRect));
if (pointNumber < belowArea)
{
return NSMakePoint(pointNumber % (int)NSWidth(greenRect) + NSMinX(greenRect),
pointNumber / (int)NSWidth(greenRect) + NSMinY(greenRect));
}
// not below - consider to left
pointNumber -= belowArea;
int leftWidth = NSMinX(blueRect) - NSMinX(greenRect);
int leftArea = NSHeight(blueRect) * leftWidth;
if (pointNumber < leftArea)
{
return NSMakePoint(pointNumber % leftWidth + NSMinX(greenRect),
pointNumber / leftWidth + NSMinY(blueRect));
}
// not left - consider to right
pointNumber -= leftArea;
int rightWidth = NSMaxX(greenRect) - NSMaxX(blueRect);
int rightArea = NSHeight(blueRect) * rightWidth;
if (pointNumber < rightArea)
{
return NSMakePoint(pointNumber % rightWidth + NSMaxX(blueRect),
pointNumber / rightWidth + NSMinY(blueRect));
}
// it must be above
pointNumber -= rightArea;
return NSMakePoint(pointNumber % (int)NSWidth(greenRect) + NSMinX(greenRect),
pointNumber / (int)NSWidth(greenRect) + NSMaxY(blueRect));
}
This is uniform, but whether it is worth it you'll have to decide.
Okay. This was bothering me, so I did the work. It's a lot of source code, but computationally lightweight and probabilistically correct (haven't tested).
With all due respect to #MartinR, I think this is superior insofar as it doesn't loop (consider the case where the contained rect covers a very large portion of the outer rect). And with all due respect to #CRD, it's a pain, but not impossible to get the desired probabilities. Here goes:
// Find a random position in rect, excluding a contained rect called exclude
//
// It looks terrible, but it's just a lot of bookkeeping.
// Divide rect into 8 regions, like a tic-tac-toe board, excluding the center square
// Reading left to right, top to bottom, call these: A,B,C,D, (no E, it's the center) F,G,H,I
// The random point must be in one of these regions, choose by throwing a random dart, using
// cumulative probabilities to choose. The likelihood that the dart will be in regions A-I is
// the ratio of each's area to the total (less the center)
// With a target rect, correctly selected, we can easily pick a random point within it.
+ (CGPoint)pointInRect:(CGRect)rect excluding:(CGRect)exclude {
// find important points in the grid
CGFloat xLeft = CGRectGetMinX(rect);
CGFloat xCenter = CGRectGetMinX(exclude);
CGFloat xRight = CGRectGetMaxX(exclude);
CGFloat widthLeft = exclude.origin.x-CGRectGetMinX(rect);
CGFloat widthCenter = exclude.size.width;
CGFloat widthRight = CGRectGetMaxY(rect)-CGRectGetMaxX(exclude);
CGFloat yTop = CGRectGetMinY(rect);
CGFloat yCenter = exclude.origin.y;
CGFloat yBottom = CGRectGetMaxY(exclude);
CGFloat heightTop = exclude.origin.y-CGRectGetMinY(rect);
CGFloat heightCenter = exclude.size.height;
CGFloat heightBottom = CGRectGetMaxY(rect)-CGRectGetMaxY(exclude);
// compute the eight regions
CGFloat areaA = widthLeft * heightTop;
CGFloat areaB = widthCenter * heightTop;
CGFloat areaC = widthRight * heightTop;
CGFloat areaD = widthLeft * heightCenter;
CGFloat areaF = widthRight * heightCenter;
CGFloat areaG = widthLeft * heightBottom;
CGFloat areaH = widthCenter * heightBottom;
CGFloat areaI = widthRight * heightBottom;
CGFloat areaSum = areaA+areaB+areaC+areaD+areaF+areaG+areaH+areaI;
// compute the normalized probabilities
CGFloat pA = areaA/areaSum;
CGFloat pB = areaB/areaSum;
CGFloat pC = areaC/areaSum;
CGFloat pD = areaD/areaSum;
CGFloat pF = areaF/areaSum;
CGFloat pG = areaG/areaSum;
CGFloat pH = areaH/areaSum;
// compute cumulative probabilities
CGFloat cumB = pA+pB;
CGFloat cumC = cumB+pC;
CGFloat cumD = cumC+pD;
CGFloat cumF = cumD+pF;
CGFloat cumG = cumF+pG;
CGFloat cumH = cumG+pH;
// now pick which region we're in, using cumulatvie probabilities
// whew, maybe we should just use MartinR's loop. No No, we've come too far!
CGFloat dart = uniformRandomUpTo(1.0);
CGRect targetRect;
// top row
if (dart < pA) {
targetRect = CGRectMake(xLeft, yTop, widthLeft, heightTop);
} else if (dart >= pA && dart < cumB) {
targetRect = CGRectMake(xCenter, yTop, widthCenter, heightTop);
} else if (dart >= cumB && dart < cumC) {
targetRect = CGRectMake(xRight, yTop, widthRight, heightTop);
}
// middle row
else if (dart >= cumC && dart < cumD) {
targetRect = CGRectMake(xRight, yCenter, widthRight, heightCenter);
} else if (dart >= cumD && dart < cumF) {
targetRect = CGRectMake(xLeft, yCenter, widthLeft, heightCenter);
}
// bottom row
else if (dart >= cumF && dart < cumG) {
targetRect = CGRectMake(xLeft, yBottom, widthLeft, heightBottom);
} else if (dart >= cumG && dart < cumH) {
targetRect = CGRectMake(xCenter, yBottom, widthCenter, heightBottom);
} else {
targetRect = CGRectMake(xRight, yBottom, widthRight, heightBottom);
}
// yay. pick a point in the target rect
CGFloat x = uniformRandomUpTo(targetRect.size.width) + CGRectGetMinX(targetRect);
CGFloat y = uniformRandomUpTo(targetRect.size.height)+ CGRectGetMinY(targetRect);
return CGPointMake(x, y);
}
float uniformRandomUpTo(float max) {
return max * arc4random_uniform(RAND_MAX) / RAND_MAX;
}
Try this code, Worked for me.
-(CGPoint)randomPointInRect:(CGRect)r
{
CGPoint p = r.origin;
p.x += arc4random_uniform((u_int32_t) CGRectGetWidth(r));
p.y += arc4random_uniform((u_int32_t) CGRectGetHeight(r));
return p;
}
I don't like piling onto answers. However, the provided solutions do not work, so I feel obliged to chime in.
Martin's is fine, and simple... which may be all you need. It does have one major problem though... finding the answer when the inner rectangle dominates the containing rectangle could take quite a long time. If it fits your domain, then always choose the simplest solution that works.
jancakes solution is not uniform, and contains a fair amount of bias.
The second solution provided by dang just plain does not work... because arc4_random takes and returns uint32_t and not a floating point value. Thus, all generated numbers should fall into the first box.
You can address that by using drand48(), but it's not a great number generator, and has bias of its own. Furthermore, if you look at the distribution generated by that method, it has heavy bias that favors the box just to the left of the "inner box."
You can easily test the generation... toss a couple of UIViews in a controller, add a button handler that plots 100000 "random" points and you can see the bias clearly.
So, I hacked up something that is not elegant, but does provide a uniform distribution of random numbers in the larger rectangle that are not in the contained rectangle.
You can surely optimize the code and make it a bit easier to read...
Caveat: Will not work if you have more than 4,294,967,296 total points. There are multiple solutions to this, but this should get you moving in the right direction.
- (CGPoint)randomPointInRect:(CGRect)rect
excludingRect:(CGRect)excludeRect
{
excludeRect = CGRectIntersection(rect, excludeRect);
if (CGRectEqualToRect(excludeRect, CGRectNull)) {
return CGPointZero;
}
CGPoint result;
uint32_t rectWidth = rect.size.width;
uint32_t rectHeight = rect.size.height;
uint32_t rectTotal = rectHeight * rectWidth;
uint32_t excludeWidth = excludeRect.size.width;
uint32_t excludeHeight = excludeRect.size.height;
uint32_t excludeTotal = excludeHeight * excludeWidth;
if (rectTotal == 0) {
return CGPointZero;
}
if (excludeTotal == 0) {
uint32_t r = arc4random_uniform(rectHeight * rectWidth);
result.x = r % rectWidth;
result.y = r /rectWidth;
return result;
}
uint32_t numValidPoints = rectTotal - excludeTotal;
uint32_t r = arc4random_uniform(numValidPoints);
uint32_t numPointsAboveOrBelowExcludedRect =
(rectHeight * excludeWidth) - excludeTotal;
if (r < numPointsAboveOrBelowExcludedRect) {
result.x = (r % excludeWidth) + excludeRect.origin.x;
result.y = r / excludeWidth;
if (result.y >= excludeRect.origin.y) {
result.y += excludeHeight;
}
} else {
r -= numPointsAboveOrBelowExcludedRect;
uint32_t numPointsLeftOfExcludeRect =
rectHeight * excludeRect.origin.x;
if (r < numPointsLeftOfExcludeRect) {
uint32_t rowWidth = excludeRect.origin.x;
result.x = r % rowWidth;
result.y = r / rowWidth;
} else {
r -= numPointsLeftOfExcludeRect;
CGFloat startX =
excludeRect.origin.x + excludeRect.size.width;
uint32_t rowWidth = rectWidth - startX;
result.x = (r % rowWidth) + startX;
result.y = r / rowWidth;
}
}
return result;
}
I'm in the course of developing a metronome for iPad. I'm using CGAffineTransformRotate for the metronomeArm animation, NSTimer(I'm not interested in great precision) for sound and a UIPanGestureRecognizer for dragging the metronomeWeight on the metronomeArm.
My problem is that I don't know how to update the bpm by dragging the weight using the pan. For now I have this : metronomeWeight.center.y is 240 and the default bpm for this position is 80.The weight goes from top 140 to a maximum of 450. I have implemented this method but it is not correct :
-(void)updateBPM
{
CGFloat weightYPosition = metronomeWeight.center.y;
NSUInteger newBPM = (weightYPosition/3);
self.bpm = newBPM;
}
and the selector for the pan is this :
-(void)handlePan:(UIPanGestureRecognizer*)gesture
{
CGPoint translation = [gesture translationInView:metronomeArm];
CGPoint location = [gesture locationInView:metronomeArm];
NSLog(#"miscarea pe oy are valoare de: %f", location.y);
CGPoint newCenter = CGPointMake(metronomeArm.frame.size.width/2, gesture.view.center.y + translation.y );
if (newCenter.y >= 140 && newCenter.y <= 450)
{
gesture.view.center = newCenter;
[gesture setTranslation:CGPointZero inView:metronomeArm];
[self updateBPMFromWeightLocation];
tempoLabel.text = [NSString stringWithFormat:#"%d", self.bpm];
NSLog(#"metronomeWeight position : %f ",metronomeWeight.center.y);
}
}
The sound and animation update but not as desired, meaning that the lower limit bpm should be 225 and the upper one should be 1. In my case they are 150 and 46 respectively.
My calculations are not good, so it will be fantastic if you can help me solve this problem... I have looked at apple's metronome project for days and can't understand how they do this...
Thanks
The new updateBPM method thanks to #zimmryan suggestion
-(void)updateBPMFromWeightLocation
{
CGFloat weightYPosition = metronomeWeight.center.y;
float lengthInM = ((weightYPosition - 140) * 0.00041333);
float time = 2 * M_PI * sqrt(lengthInM / 9.8);
NSUInteger newBPM = floor(60.0 / time);
self.bpm = newBPM;
}
From my understanding of physics and calculus, the equation for the period of a pendulum is T=2pi sqrt(l/g) where T is time in seconds, l is length in meters, and g is gravity.
You are picking a base point of 290 (pixels) and a BPM of 120. A BPM of 120 converts to a period of .5 seconds. So T = .5. Solving the equation you get .062 for l, or 6.2cm.
But your length is not in cm it is in pixels s now you have to convert it. Since your range is from 140 to 350, your zero point is 350. So first you take 350 - 390 to get an offset of 60. Now create your equation of 60pixels * k = .062 so your k = .001033
Your final function should read
-(void)updateBPM
{
CGFloat weightYPosition = metronomeWeight.center.y;
float lengthInM = ((350 - weightYPosition) * .001033);
float time = 2 * M_PI * sqrt(lengthInM / 9.8);
NSUInteger newBPM = floor(60 / time);
self.bpm = newBPM;
}
or
-(void)updateBPM
{
self.bpm = floor(60 / (2 * M_PI * sqrt(((350 - metronomeWeight.center.y) * .001033) / 9.8)));
}
I have 7 movieclips on stage I want to tween around an ellipse from different start points. I am having lots of trouble doing this.... I used a circle formula at first and then divided the y value by the width of the ellipse over the height. This sort of worked but after every rotation the y value was a little of. That code is:
this._x += (Math.cos(angle * Math.PI/180) * radius);
this._y += (Math.sin(angle * Math.PI/180) *radius)/1.54;
I also have trouble finding the angle of the start point, if it is off they won't travel in the same ellipse but they all have different starting angles.
Any clues?
Calculate the incidvidual offsets using this snippet:
// assuming you have your buttons in an array called buttons
for (var i:Number = 0; i < buttons.length; i++){
buttons[i].angleOffset = 360 / buttons.length * i;
}
Set the position each update instead of moving, that way you wont get any drift.
Update each object using this code, incrementing the angle var to get it to spin.
this._x = offsetX + Math.sin((angle + angleOffset) * Math.PI/180) * radius;
this._y = offsetY + Math.cos((angle + angleOffset) * Math.PI/180) * radius / 1.54;
This is almost soved, this piece of script will take the items of the array buttons (can add as many as you want), space them around the ellipse you set (origin + radius), and tween them around it according to the speed you set. The only problem is the spacing isn't even and some are close and some far apart and I don't understand why.
var angle:Number = 0;
var originX:Number = 200;
var originY:Number = 200;
var radiusX:Number = 267.5;
var radiusY:Number = 100;
var steps:Number = 360;
var speed:Number = 3.1415/steps;
var buttons:Array = new Array(this.age,this.ethnicity,this.sex,this.social,this.ability,this.orientation,this.faith);
for (i=0;i<buttons.length;i++) {
buttons[i].onEnterFrame = function() {
moveButtons(this);
controllButtons(this);
};
buttons[i]._order = (360/buttons.length) * (i+1);
}
function moveButtons(e) {
e._anglePhase = angle+e._order;
e._x = originX+Math.sin(e._anglePhase)*radiusX;
e._y = originY+Math.cos(e._anglePhase)*radiusY;
}
function controllButtons(e) {
angle += speed;
if (angle>=360) {
angle -= 360;
}
}
Please note I got the base of this script from http://www.actionscript.org/forums/showthread.php3?t=161830&page=2 converted it to AS2 and made it work from an array.