CODEWITHSUNDEEP
iosobjective-cgeometryuibezierpath
samouray
samouray

Reputation: 578

Objective C - how to know if point is inside a quarter of circle?

I drew a quarter of a circle inside a rectangle.

Rectangle:

UIView *Rectangle  = [[UIView alloc] initWithFrame:CGRectMake(0,0,[[UIScreen mainScreen] bounds].size.width,[[UIScreen mainScreen] bounds].size.height-292)];
    Rectangle.backgroundColor = [UIColor lightGrayColor];
    Rectangle.layer.zPosition = -5;

Quarter of Cirlce:

CGPoint center;
center.x = 0;
center.y = 0;
float radius = [[UIScreen mainScreen] bounds].size.width;

UIBezierPath *circle = [UIBezierPath bezierPathWithArcCenter:center
                                                      radius:radius
                                                  startAngle:0
                                                    endAngle:M_PI
                                                   clockwise:YES];
CAShapeLayer *circleLayer = [CAShapeLayer layer];
[circleLayer setPath:[circle CGPath]];

Then I added the rectangle in the view and added the circle inside the rectangle:

[self.view addSubview:Rectangle];
[Rectangle.layer addSublayer:circleLayer];

Then I started drawing little rectangles of 1 width and 1 height that I consider as points, and randomly added them into the view with a for loop, coloring the points inside the circle with green and points outside of the circle with red

int compteurPointsinCercle  = 0 ;
    int compteurPointsOutCercle  = 0 ;
    float       XcenterCircle   =   center.x;
    float       YcenterCircle   =   center.y;

    for (int i = 0 ; i < 50000 ; i++ )
    {

        float xvalue = arc4random_uniform([[UIScreen mainScreen] bounds].size.width);
        float yvalue = arc4random_uniform([[UIScreen mainScreen] bounds].size.height-292);

              // (x - center_x)^2 + (y - center_y)^2 < radius^2
        float valeurPoint = (xvalue - XcenterCircle)*2 + (yvalue -YcenterCircle)*2;

        NSLog(@"(Inside for), valeurPoint is : %f",valeurPoint);


        if ( valeurPoint <  (radius*2) )
        {
            // Point is inside of circle (green color)
            compteurPointsinCercle++;
            UIView *Rectangle2  = [[UIView alloc] initWithFrame:CGRectMake(xvalue,yvalue,1,1)];
            Rectangle2.backgroundColor = [UIColor greenColor];
            [self.view addSubview:Rectangle2];
        }
        else if ( valeurPoint > (radius*2) )
        {
            // Point is outside of circle (red color)
            compteurPointsOutCercle++;
            UIView *Rectangle2  = [[UIView alloc] initWithFrame:CGRectMake(xvalue,yvalue,1,1)];
            Rectangle2.backgroundColor = [UIColor redColor];
            [self.view addSubview:Rectangle2];
        }


    }

I test if the point is inside the circle using this : 

 float valeurPoint = (xvalue - XcenterCircle)*2 + (yvalue -YcenterCircle)*2;

where xvalue and yvalue are the coordinates of the point that will be created, and XcenterCircle and YcenterCircle are the coordiantes of the center of the circle.

I have something wrong because it gives me this result (it dosent test correctly if the point is inside the circle or not: a part of the points inside of the circle are considered outside):

enter image description here

can you tell me what I am doing wrong here ? and how can I exactly the points inside the circle ?

Upvotes: 0

Views: 868

Answers (1)

Sulthan
Sulthan

Reputation: 130102

* is not power operation, it is multiplication.

float valeurPoint = (xvalue - XcenterCircle) * (xvalue - XcenterCircle) + (yvalue -YcenterCircle)*(yvalue -YcenterCircle);

if ( valeurPoint <  (radius * radius) )

Should fix your problem

or using the pow function:

float valeurPoint = pow((xvalue - XcenterCircle), 2) + pow((yvalue -YcenterCircle), 2);

You can also use hypot function directly (although the performance can be slightly worse because of sqrt calculation)

float distance = hypotf((xvalue - XcenterCircle), (yvalue -YcenterCircle));

if (distance < radius)

EDIT: Thanks @Alex for suggestion. The best solution is to use the native method -[UIBerierPath containsPoint:]. Then you won't have to calculate the distance at all.

Upvotes: 2

Related Questions