text labels drawn in CGRect form an elliptical arc when images drawn using the same coordinates form a circular arc

问题

I am new to Core Graphics and trying to understand why text labels I draw in CGRect form an elliptical arc when images I draw using the same coordinates form a circular arc.

The original code by Arthur Knopper creates circles wherever the screen is touched. By removing the touches method, I have been able to generate a series of small circles (dots) along a circular arc (uber circle). Each dot is centred on the perimeter of the uber circle (as shown below).

In order to label each dot I use the same point coordinates I used for placing the dot. However text labels form an elliptical arc even though dots form a circular arc (as shown below). Labels are also hidden by the dots when dots are filled. The reason for this is a complete mystery.

As a novice I am probably missing something basic in Core Graphics. If anyone could explain what that is and what I need to do to make both arcs circular and place labels on top of the dots I’d be most grateful.

Thanks.

Here is the code.

    circleView.h

    NSMutableArray  *totalCircles;

    int            dotCount, limit;

    float         uberX, uberY, uberRadius, uberAngle, labelX,
                    labelY,dotRadius, dotsFilled, sectors, x, y;

    CGPoint         dotPosition;
    CGRect          boxBoundary;
    CGContextRef    context;
}

- (void)demo;

@end

And ...

-@implementation iOSCircleView

- (id)initWithFrame:(CGRect)frame   {
    self = [super initWithFrame:frame];
    if (self) {

        // Initialization code
        totalCircles            = [[NSMutableArray alloc] init];

        // Set background color
        self.backgroundColor    = [UIColor whiteColor];
    }
    return self;
}   // frame a view for drawing



- (void)drawRect:(CGRect)rect       {
     [self demo];
}


- (void)demo                        {
        context          = UIGraphicsGetCurrentContext();
        CGContextSetLineWidth(context, 0.5);

        uberX           =   120;
        uberY           =   160;
        uberRadius      =   30;
        sectors         =   16;
        uberAngle       =   (2.0 * PI) / sectors;

        dotRadius       =   20;
        dotsFilled      =   FALSE;

        for (dotCount   = 1; dotCount <= sectors; dotCount++)
        {
            // Create a new iOSCircle Object
            iOSCircle *newCircle    = [[iOSCircle alloc] init];
            newCircle.circleRadius  = dotRadius;
            [self setSectorDotCoordinates];        // make new point for each dot
            dotPosition             = CGPointMake(x,y);         // create each dot

            NSLog(@"Circle%i: %@", dotCount, NSStringFromCGPoint(dotPosition));

            [self autoLabel];                      // text hides behind the dots

            newCircle.circleCentre  = dotPosition; // place each dot on the frame
            [totalCircles addObject:newCircle];
            [self setNeedsDisplay];
        }

        CGContextSetShadowWithColor(context, CGSizeMake(-3 , 2), 4.0, [UIColor clearColor].CGColor);
        dotCount = 1;
        for (iOSCircle *circle in totalCircles) {
            CGContextAddArc(context, circle.circleCentre.x, circle.circleCentre.y, circle.circleRadius, 0.0, M_PI * 2.0, YES);               // draw the circles

            NSLog(@"Dot %i Filled %i ", dotCount, dotsFilled);
            switch (dotsFilled) {
                case 1:
                    CGContextSetFillColorWithColor(context, [[UIColor cyanColor] CGColor]);
                    //CGContextDrawPath(context, kCGPathFillStroke);
                    break;
                    default:
                    //CGContextStrokePath(context);    // draw dot outline
                    break;
            }
            dotCount++;
        }
    }   //  draw circular dots in circular patterns

- (void)setSectorDotCoordinates     {

    x           = uberX + (uberRadius * cos(uberAngle *dotCount) * 2);
    y           = uberY + (uberRadius * sin(uberAngle *dotCount) * 2);    
}   // calculate dot coordinates along a circular arc

- (void)autoLabel {
    CGContextSetStrokeColorWithColor(context, [[UIColor blackColor] CGColor]);
    boxBoundary = CGRectMake(x-dotRadius, y-dotRadius, x+dotRadius, y+dotRadius);
    [[NSString stringWithFormat:@"%i",dotCount] drawInRect:boxBoundary withFont:[UIFont systemFontOfSize:24] lineBreakMode:NSLineBreakByCharWrapping alignment:NSTextAlignmentCenter];
}

回答1:

Change the boxBoundary in autoLabel, CGRectMake creates a rectangle with one point coordinates and width and height, not two points:

(void)autoLabel { 
 CGContextSetStrokeColorWithColor(context, [[UIColor blackColor] CGColor]);
 boxBoundary = CGRectMake(x-dotRadius, y-dotRadius, dotRadius*2, dotRadius*2); 
 [[NSString stringWithFormat:@"%i",dotCount] drawInRect:boxBoundary 
                                             withFont:[UIFont systemFontOfSize:24] 
                                        lineBreakMode:NSLineBreakByCharWrapping alignment:NSTextAlignmentCenter]; 
}

In your code the "boxes" containing the texts where bigger and bigger when you where going to the right. (the width and height were not fixed)

来源：https://stackoverflow.com/questions/28165369/text-labels-drawn-in-cgrect-form-an-elliptical-arc-when-images-drawn-using-the-s

标签

ios

objective-c

cgrect