在sizeToFit之后将字形对齐到UITextView的顶部

Question

我正在开发的应用程序支持数百种不同的字体。其中一些字体，特别是脚本字体，具有重要的上升和下降。当使用某些字体在sizeToFit()上调用UITextView时，我最终得到了显着的顶部和底部填充（左侧图像）。目标是最终得到右侧的图像，以便最高的字形与文本视图的边界框的顶部齐平。

这是上图中的日志：

Point Size: 59.0
Ascender:  70.21
Descender:  -33.158
Line Height:  103.368
Leading: 1.416
TextView Height: 105.0

我的第一个想法是查看文本第一行中每个字形的高度，然后计算容器顶部和最高字形顶部之间的偏移量。然后我可以使用textContainerInset相应地调整上边距。

我在我的UITextView子类中尝试过类似的东西：

for location in 0 ..< lastGlyphIndexInFirstLine {
    let glphyRect = self.layoutManager.boundingRect(forGlyphRange: NSRange(location: location, length: 1), in: self.textContainer)
    print(glphyRect.size.height) // prints 104.78399999999999 for each glyph
}

不幸的是，这不起作用，因为boundRect(forGlyphRange:in:)似乎没有返回字形本身的矩形（我猜这总是相同的值，因为它返回行片段的高度？）。

这是解决这个问题最简单的方法吗？如果是，我如何计算文本视图顶部与第一行文本中最高字形顶部之间的距离？

Answer 1

使用TextKit似乎不可能，但可以直接使用CoreText。具体来说，CGFont的getGlyphBBoxes以字形空间为单位返回正确的矩形，然后可以将其转换为相对于字体大小的点。

感谢this answer让我意识到getGlyphBBoxes以及记录如何将结果rect转换为积分。

以下是完整的解决方案。这假设您有一个UITextView子类，事先具有以下设置：

self.contentInset = .zero
self.textContainerInset = .zero
self.textContainer.lineFragmentPadding = 0.0

此函数现在将返回从文本视图边界顶部到最高使用字形顶部的距离：

private var distanceToGlyphs: CGFloat {
    // sanity
    guard
        let font = self.font,
        let fontRef = CGFont(font.fontName as CFString),
        let attributedText = self.attributedText,
        let firstLine = attributedText.string.components(separatedBy: .newlines).first
    else { return 0.0 }

    // obtain the first line of text as an attributed string
    let attributedFirstLine = attributedText.attributedSubstring(from: NSRange(location: 0, length: firstLine.count)) as CFAttributedString

    // create the line for the first line of attributed text
    let line = CTLineCreateWithAttributedString(attributedFirstLine)

    // get the runs within this line (there will typically only be one run when using a single font)
    let glyphRuns = CTLineGetGlyphRuns(line) as NSArray
    guard let runs = glyphRuns as? [CTRun] else { return 0.0 }

    // this will store the maximum distance from the baseline
    var maxDistanceFromBaseline: CGFloat = 0.0

    // iterate each run
    for run in runs {
        // get the total number of glyphs in this run
        let glyphCount = CTRunGetGlyphCount(run)

        // initialize empty arrays of rects and glyphs
        var rects = Array<CGRect>(repeating: .zero, count: glyphCount)
        var glyphs = Array<CGGlyph>(repeating: 0, count: glyphCount)

        // obtain the glyphs
        self.layoutManager.getGlyphs(in: NSRange(location: 0, length: glyphCount), glyphs: &glyphs, properties: nil, characterIndexes: nil, bidiLevels: nil)

        // obtain the rects per-glyph in "glyph space units", each of which needs to be scaled using units per em and the font size
        fontRef.getGlyphBBoxes(glyphs: &glyphs, count: glyphCount, bboxes: &rects)

        // iterate each glyph rect
        for rect in rects {
            // obtain the units per em from the font ref so we can convert the rect
            let unitsPerEm = CGFloat(fontRef.unitsPerEm)

            // sanity to prevent divide by zero
            guard unitsPerEm != 0.0 else { continue }

            // calculate the actual distance up or down from the glyph's baseline
            let glyphY = (rect.origin.y / unitsPerEm) * font.pointSize

            // calculate the actual height of the glyph
            let glyphHeight = (rect.size.height / unitsPerEm) * font.pointSize

            // calculate the distance from the baseline to the top of the glyph
            let glyphDistanceFromBaseline = glyphHeight + glyphY

            // store the max distance amongst the glyphs
            maxDistanceFromBaseline = max(maxDistanceFromBaseline, glyphDistanceFromBaseline)
        }
    }

    // the final top margin, calculated by taking the largest ascender of all the glyphs in the font and subtracting the max calculated distance from the baseline
    return font.ascender - maxDistanceFromBaseline
}

您现在可以将文本视图的顶部contentInset设置为-distanceToGlyphs以获得所需的结果。