如何找到获得所需的lineHeight或其他指标所需的UIFont pointSize?

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问题描述

您可以向 UIFont 实例询问其 lineHeight 指标:

You can ask a UIFont instance for its lineHeight metric:

UIFont *const font = [UIFont systemFontOfSize: 10];
CGFloat lineHeight = [font lineHeight];

如果我想要特定的lineHeight(例如20)，如何创建具有该大小的UIFont?

If I want a particular lineHeight, (20, say), how can I create a UIFont with that size?

答案

令我惊讶的是，我的有限分析表明可以使用线性插值.这是 UIFont 上的类别，它将执行所需的操作:

Answer

My limited analysis suggests, surprisingly to me, that linear interpolation can be used. Here's a category on UIFont that will do what's needed:

@interface UIFont (FontWithLineHeight)
+(UIFont*) systemFontWithLineHeight: (CGFloat) lineHeight;
@end

具有实现方式:

@implementation UIFont (FontWithLineHeight)
+(UIFont*) systemFontWithLineHeight:(CGFloat)lineHeight
{
  const CGFloat lineHeightForSize1 = [[UIFont systemFontOfSize: 1] lineHeight];
  const CGFloat pointSize = lineHeight / lineHeightForSize1;
  return [UIFont systemFontOfSize: pointSize];
}
@end

像这样使用:

UIFont *const font = [UIFont systemFontWithLineHeight: 20];
NSLog(@"%f", [font lineHeight]);

哪个输出:

2014-01-08 16:04:19.614 SpikeCollectionView[6309:60b] 20.000000

要求的是什么.

似乎 UIFont 的 lineHeight 与 pointSize 呈线性比例关系.换句话说，如果将 pointSize 设置为两倍，则 lineHeight 的设置也将为两倍.如果将 pointSize 减半，则还将 lineHeight 减半.这意味着可以使用插值来找到将提供给定 lineHeight 或其他指标的 pointSize .

It seems that the lineHeight of a UIFont scales linearly with the pointSize. In other words, if you make the pointSize twice as much, then the lineHeight will be twice as much too. If you halve the pointSize you also halve the lineHeight. This means that interpolation can be used to find the pointSize that will provide a given lineHeight or other metric.

以下代码显示线性度:

const CGFloat lineHeight1 = [[UIFont systemFontOfSize: 1] lineHeight];
const CGFloat lineHeight10 = [[UIFont systemFontOfSize: 10] lineHeight];
const CGFloat lineHeight100 = [[UIFont systemFontOfSize: 100] lineHeight];
const CGFloat ratio1_10 = lineHeight10 / lineHeight1;
const CGFloat ratio10_100 = lineHeight100 / lineHeight10;
NSLog(@"%f", ratio1_10);
NSLog(@"%f", ratio10_100);

输出为:

2014-01-08 15:56:39.326 SpikeCollectionView[6273:60b] 9.999999
2014-01-08 15:56:39.329 SpikeCollectionView[6273:60b] 10.000001

警告

我仅针对iOS 7上的系统字体对此进行了测试.其他字体在缩放至它们的pointSize时可能无法显示其指标的线性缩放.如果有人可以确认这是否可以保证或什么时候不起作用，那将是奇妙的.如果您尝试将其用于其他 UIFont ，但此方法不起作用，请注释或扩展此答案，或添加另一个答案.

Caution

I've only tested this for the system font on iOS 7. Other fonts may not exhibit linear scaling of their metrics under scalings to their pointSize. If someone could confirm whether this is guaranteed or when it won't work, that would be marvellous. If you try this for other UIFont and it doesn't work, please comment or extend this answer, or add another.

如果不能保证指标的线性缩放，则必须搜索所需的 pointSize .您将需要一个求根"数字算法.伊利诺伊算法适用于此.

If linear scaling of the metrics is not guaranteed, it would be necessary to search for the required pointSize. You will need a "root finding" numeric algorithm. The Illinois Algorithm would work for this.

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PointSize