react-native/ReactCommon/fabric/textlayoutmanager/platform/ios/NSTextStorage+FontScaling.m

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#import "NSTextStorage+FontScaling.h"

typedef NS_OPTIONS(NSInteger, RCTTextSizeComparisonOptions) {
  RCTTextSizeComparisonSmaller = 1 << 0,
  RCTTextSizeComparisonLarger = 1 << 1,
  RCTTextSizeComparisonWithinRange = 1 << 2,
};

@implementation NSTextStorage (FontScaling)

- (void)scaleFontSizeToFitSize:(CGSize)size
               minimumFontSize:(CGFloat)minimumFontSize
               maximumFontSize:(CGFloat)maximumFontSize {
  CGFloat bottomRatio = 1.0 / 128.0;
  CGFloat topRatio = 128.0;
  CGFloat ratio = 1.0;

  NSAttributedString *originalAttributedString = [self copy];

  CGFloat lastRatioWhichFits = 0.02;

  while (true) {
    [self scaleFontSizeWithRatio:ratio
                 minimumFontSize:minimumFontSize
                 maximumFontSize:maximumFontSize];

    RCTTextSizeComparisonOptions comparsion = [self compareToSize:size
                                                   thresholdRatio:0.01];

    if ((comparsion & RCTTextSizeComparisonWithinRange) &&
        (comparsion & RCTTextSizeComparisonSmaller)) {
      return;
    } else if (comparsion & RCTTextSizeComparisonSmaller) {
      bottomRatio = ratio;
      lastRatioWhichFits = ratio;
    } else {
      topRatio = ratio;
    }

    ratio = (topRatio + bottomRatio) / 2.0;

    CGFloat kRatioThreshold = 0.005;
    if (ABS(topRatio - bottomRatio) < kRatioThreshold ||
        ABS(topRatio - ratio) < kRatioThreshold ||
        ABS(bottomRatio - ratio) < kRatioThreshold) {
      [self replaceCharactersInRange:(NSRange){0, self.length}
                withAttributedString:originalAttributedString];

      [self scaleFontSizeWithRatio:lastRatioWhichFits
                   minimumFontSize:minimumFontSize
                   maximumFontSize:maximumFontSize];
      return;
    }

    [self replaceCharactersInRange:(NSRange){0, self.length}
              withAttributedString:originalAttributedString];
  }
}

- (RCTTextSizeComparisonOptions)compareToSize:(CGSize)size
                               thresholdRatio:(CGFloat)thresholdRatio {
  NSLayoutManager *layoutManager = self.layoutManagers.firstObject;
  NSTextContainer *textContainer = layoutManager.textContainers.firstObject;

  [layoutManager ensureLayoutForTextContainer:textContainer];

  // Does it fit the text container?
  NSRange glyphRange = [layoutManager glyphRangeForTextContainer:textContainer];
  NSRange truncatedGlyphRange = [layoutManager
      truncatedGlyphRangeInLineFragmentForGlyphAtIndex:glyphRange.length - 1];

  if (truncatedGlyphRange.location != NSNotFound) {
    return RCTTextSizeComparisonLarger;
  }

  CGSize measuredSize =
      [layoutManager usedRectForTextContainer:textContainer].size;

  // Does it fit the size?
  BOOL fitsSize =
      size.width >= measuredSize.width && size.height >= measuredSize.height;

  CGSize thresholdSize = (CGSize){
      size.width * thresholdRatio,
      size.height * thresholdRatio,
  };

  RCTTextSizeComparisonOptions result = 0;

  result |=
      (fitsSize) ? RCTTextSizeComparisonSmaller : RCTTextSizeComparisonLarger;

  if (ABS(measuredSize.width - size.width) < thresholdSize.width) {
    result = result | RCTTextSizeComparisonWithinRange;
  }

  return result;
}

- (void)scaleFontSizeWithRatio:(CGFloat)ratio
               minimumFontSize:(CGFloat)minimumFontSize
               maximumFontSize:(CGFloat)maximumFontSize {
  [self beginEditing];

  [self
      enumerateAttribute:NSFontAttributeName
                 inRange:(NSRange){0, self.length}
                 options:
                     NSAttributedStringEnumerationLongestEffectiveRangeNotRequired
              usingBlock:^(
                  UIFont *_Nullable font, NSRange range, BOOL *_Nonnull stop) {
                if (!font) {
                  return;
                }

                CGFloat fontSize =
                    MAX(MIN(font.pointSize * ratio, maximumFontSize),
                        minimumFontSize);

                [self addAttribute:NSFontAttributeName
                             value:[font fontWithSize:fontSize]
                             range:range];
              }];

  [self endEditing];
}

@end