Question

我必须为配镜师编程看看测试。所以他们需要数字确切地具有特定的高度。他有一个iPad将其流式传输到电视上。我知道我必须考虑电视的PPI。这是我的代码：

func calcPoints() -> Float {
    // he gives the Visus with a TextField
    let visus = Float(textFieldVisus.text!)
    // Here you put in the PPI of the device
    let ppi = Float(textFieldDPI.text!)
    // Calculate the lenght of the Number
    let lenght = ((0.29 * 5) / visus!) * 5
    // Calculate the Points (because TextFiels work with Points)
    let points = ((ppi! / 25.4) * lenght) * 0.75
    // here you divide with 2 because you have a retina Display on the IPad
    return (points / 2)
}

func passeUIan() {
    // Now i can give the Points to the TextField
    textField1.bounds.size.width = CGFloat(calcPoints())
    textField1.bounds.size.height = CGFloat(calcPoints())
    textField1.font = UIFont(name: (textField1.font?.fontName)!, size: CGFloat(calcPoints()))
}

但是当我测量电视上的长度时，这是错误的。 Normaly它必须是7.25mm，但它大约是9mm。我不知道出了什么问题。我从2个星期开始搜索这个问题...

Answer 1

您需要先熟悉different font metrics。字体大小通常（但不总是）上升和下降之间的差异。为了您的目的，大写字母的高度称为“上限高度”，小写字母的高度称为“x高度”。

没有将字体大小转换为上限高度或x高度的公式。他们的关系不同于字体，甚至是字体内的变体（粗体，斜体，小型大写字母，显示，书籍）。

下面的函数使用二进制搜索来查找与您所需高度（以英寸为单位）匹配的磅值：

// desiredHeight is in inches
func pointSize(inFontName fontName: String, forDesiredCapHeight desiredHeight: CGFloat, ppi: CGFloat) -> CGFloat {
    var minPointSize: CGFloat = 0
    var maxPointSize: CGFloat = 5000
    var pointSize = (minPointSize + maxPointSize) / 2

    // Finding for exact match may not be possible. UIFont may round off
    // the sizes. If it's within 0.01 in (0.26 mm) of the desired height,
    // we consider that good enough
    let tolerance: CGFloat = 0.01

    while let font = UIFont(name: fontName, size: pointSize) {
        let actualHeight = font.capHeight / ppi * UIScreen.main.scale

        if abs(actualHeight - desiredHeight) < tolerance {
            return pointSize
        } else if actualHeight < desiredHeight {
            minPointSize = pointSize
        } else {
            maxPointSize = pointSize
        }

        pointSize = (minPointSize + maxPointSize) / 2
    }

    return 0
}

示例：在Helvetica中找到使大写字母高1英寸的磅值。（326是iPhone 6 / 6S / 7的PPI，我曾经测试过）：

let size = pointSize(inFontName: "Helvetica", forDesiredCapHeight: 1, ppi: 326)
label.font = UIFont(name: fontName, size: size)
label.text = "F"

（提示：UILabel处理字体大小比UITextField更好

在TextField中显示文本的高度

1 个答案: