ios - 使用 CoreText 呈现字符串时的字距调整问题

Question

我正在尝试使用 CoreText api 呈现字符串。每个字符都在 CAShapeLayer 中呈现，我正在为每个字符获取图层偏移(x 坐标)，如下所示:

let offset = CTLineGetOffsetForStringIndex(line, glyphIndex, nil)

但是生成的偏移量似乎不符合字母之间的字距调整。这是我的意思的图像 - 顶部标签是 UILabel，底部是我的自定义渲染:

如您所见，我的自定义标签中的“A”字母离“W”字母更远。

如果有任何帮助，我将不胜感激。提前致谢。

Answer 1

万一有人遇到同样的问题，我使用了这个地方的方法:https://github.com/MichMich/XMCircleType/blob/master/XMCircleType/Views/XMCircleTypeView.m , kerningForCharacter 函数。这是函数本身:

- (float)kerningForCharacter:(NSString *)currentCharacter afterCharacter:(NSString *)previousCharacter
{
    //Create a unique cache key
    NSString *kerningCacheKey = [NSString stringWithFormat:@"%@%@", previousCharacter, currentCharacter];

    //Look for kerning in the cache dictionary
    NSNumber *cachedKerning = [self.kerningCacheDictionary objectForKey:kerningCacheKey];

    //If kerning is found: return.
    if (cachedKerning) {
        return [cachedKerning floatValue];
    }

    //Otherwise, calculate.
    float totalSize = [[NSString stringWithFormat:@"%@%@", previousCharacter, currentCharacter] sizeWithAttributes:self.textAttributes].width;
    float currentCharacterSize = [currentCharacter sizeWithAttributes:self.textAttributes].width;
    float previousCharacterSize = [previousCharacter sizeWithAttributes:self.textAttributes].width;

    float kerning = (currentCharacterSize + previousCharacterSize) - totalSize;

    //Store kerning in cache.
    [self.kerningCacheDictionary setValue:@(kerning) forKey:kerningCacheKey];

    //Return kerning.
    return kerning;
}