CircularTextView (as seen in the iOS app Blackbox)

CircularTextView.h

//
//  CircularTextView.h
//  Wormhole
//
//  Created by Ryan McLeod on 5/5/15.
//  Copyright (c) 2015 Ryan McLeod. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface CircularTextView : UIView

@property (strong, nonatomic) NSAttributedString *attributedText;
@property CGFloat inset;

@end

CircularTextView.m

//
//  CircularTextView.m
//  Wormhole
//
//  Created by Ryan McLeod on 5/5/15.
//  Copyright (c) 2015 Ryan McLeod. All rights reserved.
//

#import "CircularTextView.h"
#import <CoreText/CoreText.h>

@implementation CircularTextView

@synthesize attributedText = _attributedText;

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        NSAssert((self.bounds.size.width == self.bounds.size.height), @"%@ can only draw using a square frame!", [self class]);
    }
    return self;
}

- (NSAttributedString*) attributedText {
    return _attributedText;
}

- (void) setAttributedText:(NSAttributedString *)attributedText {
    _attributedText = attributedText;
    [self setNeedsDisplay];
}

// Modified from: https://invasivecode.com/weblog/core-text
- (void) drawRect:(CGRect)rect {
    
    [super drawRect:rect];
    
    if (!self.attributedText) {
        return;
    }
    
    CGFloat radius = self.bounds.size.width/2.f;
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
    
    CGContextTranslateCTM(context, radius, radius);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextRotateCTM(context, M_PI_2);
 
    CTLineRef line = CTLineCreateWithAttributedString((CFAttributedStringRef)self.attributedText);
    CFIndex glyphCount = CTLineGetGlyphCount(line);
    CFArrayRef runArray = CTLineGetGlyphRuns(line);
    CFIndex runCount = CFArrayGetCount(runArray);
    
    NSMutableArray *widthArray = [[NSMutableArray alloc] init];
    
    CFIndex glyphOffset = 0;
    for (CFIndex i = 0; i < runCount; i++) {
        CTRunRef run = (CTRunRef)CFArrayGetValueAtIndex(runArray, i);
        CFIndex runGlyphCount = CTRunGetGlyphCount((CTRunRef)run);
        for (CFIndex runGlyphIndex = 0; runGlyphIndex < runGlyphCount; runGlyphIndex++) {
            NSNumber *widthValue = [NSNumber numberWithDouble:CTRunGetTypographicBounds((CTRunRef)run, CFRangeMake(runGlyphIndex, 1), NULL, NULL, NULL)];
            NSAssert(widthValue, @"widthValue was nil");
            [widthArray insertObject:widthValue atIndex:(runGlyphIndex + glyphOffset)];
        }
        glyphOffset = runGlyphCount + 1;
    }
    
    CGFloat lineLength = CTLineGetTypographicBounds(line, NULL, NULL, NULL);
    
    NSMutableArray *angleArray = [[NSMutableArray alloc] init];
    
    CGFloat prevHalfWidth =  [[widthArray objectAtIndex:0] floatValue] / 2.0;
    NSNumber *angleValue = [NSNumber numberWithDouble:(prevHalfWidth / lineLength) * 2 * M_PI];
    NSAssert(angleValue, @"angleValue was nil");
    [angleArray insertObject:angleValue atIndex:0];
    
    for (CFIndex lineGlyphIndex = 1; lineGlyphIndex < glyphCount; lineGlyphIndex++) {
        CGFloat halfWidth = [[widthArray objectAtIndex:lineGlyphIndex] floatValue] / 2.0;
        CGFloat prevCenterToCenter = prevHalfWidth + halfWidth;
        // spread over whole circle:
        // NSNumber *angleValue = [NSNumber numberWithDouble:(prevCenterToCenter / lineLength) * 2 * M_PI];
        // actually spaced in a way that makes sense:
        NSNumber *angleValue = [NSNumber numberWithDouble:(atan2(prevCenterToCenter/2.f, radius) * 2)];
        
        NSAssert(angleValue, @"angleValue was nil");
        [angleArray insertObject:angleValue atIndex:lineGlyphIndex]; // 15-4
        prevHalfWidth = halfWidth;
    }
    
    
    // Warning: This will not work as expected for strings with mixed fonts/sizes!
    // Calculate line height from the first run in the string
    CTFontRef fontRef = CFAttributedStringGetAttribute((CFAttributedStringRef)self.attributedText, 0, kCTFontAttributeName, NULL);
    CGFloat lineHeight = 0.0;
    lineHeight = CTFontGetAscent(fontRef) + CTFontGetDescent(fontRef) + CTFontGetLeading(fontRef);
    
    // TODO: use actual height of font
    CGPoint textPosition = CGPointMake(0.0, radius - lineHeight - self.inset);
    CGContextSetTextPosition(context, textPosition.x, textPosition.y);
    
    glyphOffset = 0;
    for (CFIndex runIndex = 0; runIndex < runCount; runIndex++) {
        CTRunRef run = (CTRunRef)CFArrayGetValueAtIndex(runArray, runIndex);
        CFIndex runGlyphCount = CTRunGetGlyphCount(run);
        CTFontRef runFont = CFDictionaryGetValue(CTRunGetAttributes(run), kCTFontAttributeName);
        for (CFIndex runGlyphIndex = 0; runGlyphIndex < runGlyphCount; runGlyphIndex++) {
            
            CFRange glyphRange = CFRangeMake(runGlyphIndex, 1);
            
            CGContextRotateCTM(context, -[[angleArray objectAtIndex:(runGlyphIndex + glyphOffset)] floatValue]); // 16-4
            
            CGFloat glyphWidth = [[widthArray objectAtIndex:(runGlyphIndex + glyphOffset)] floatValue];
            CGFloat halfGlyphWidth = glyphWidth / 2.0;
            CGPoint positionForThisGlyph = CGPointMake(textPosition.x - halfGlyphWidth, textPosition.y); // 17-4
            
            textPosition.x -= glyphWidth;
            
            CGAffineTransform textMatrix = CTRunGetTextMatrix(run);
            textMatrix.tx = positionForThisGlyph.x; textMatrix.ty = positionForThisGlyph.y;
            CGContextSetTextMatrix(context, textMatrix);
            
            CGFontRef cgFont = CTFontCopyGraphicsFont(runFont, NULL);
            CGGlyph glyph; CGPoint position;
            CTRunGetGlyphs(run, glyphRange, &glyph);
            CTRunGetPositions(run, glyphRange, &position);
            
            CGContextSetFont(context, cgFont);
            CGContextSetFontSize(context, CTFontGetSize(runFont));
            
            CGContextSetRGBFillColor(context, 0.9, 0.9, 0.9, 1.0);
            CGContextShowGlyphsAtPositions(context, &glyph, &position, 1); 
            
            CGFontRelease(cgFont);
        }
        glyphOffset += runGlyphCount;
    }

    CFRelease(line);
}

@end