Paint.FontMetrics

top, bottom, ascent, decent 皆以baseline为基准计算，所以top, ascent为负数

• top：给定文本大小的字体中最高字形在基线之上的最大距离。
• ascent：高于基线的推荐距离。
• decent：对于单独间隔的文本，建议低于基线的距离。
• bottom：在给定文本大小下，字体中最低字形低于基线的最大距离。
• leading：建议在文本行之间添加的额外空间。（行距）

字体高度一般用 decent - ascent

效果图（Y为baseline）

效果图

20211223_132023658_0.png

override fun onDraw(canvas: Canvas?) {
    super.onDraw(canvas)
    canvas?.also {
        val str = "abcdefg字体?∑"
        val x = 300f
        val y = 200f
        val textPaint = Paint()
        textPaint.textSize = 75f
        textPaint.color = 0xff3060f0.toInt()
        val fontMetrics = textPaint.getFontMetrics()
        it.drawText(str, x, y, textPaint)
        paint.textSize = 45f
        paint.color = 0xff303030.toInt()
        it.drawLine(x, 0f, x, height.toFloat(), paint)
        it.drawLine(x, y, width.toFloat(), y, paint)
        it.drawText("XY", 10f, 60f, paint)

        paint.color = 0xff30f030.toInt()
        it.drawLine(x, y+fontMetrics.top, width.toFloat(), y+fontMetrics.top, paint)
        it.drawLine(x, y+fontMetrics.bottom, width.toFloat(), y+fontMetrics.bottom, paint)
        it.drawText("Y+Top", 10f, 120f, paint)
        it.drawText("Y+Bottom", 10f, 180f, paint)

        paint.color = 0xfff030f0.toInt()
        it.drawLine(x, y+fontMetrics.ascent, width.toFloat(), y+fontMetrics.ascent, paint)
        it.drawLine(x, y+fontMetrics.descent, width.toFloat(), y+fontMetrics.descent, paint)
        it.drawText("Y+ascent", 10f, 240f, paint)
        it.drawText("Y+decent", 10f, 300f, paint)
        
        Log.e(TAG, "onDraw() X:\t" + x)
        Log.e(TAG, "onDraw() Y:\t" + y)
        Log.e(TAG, "onDraw() fontMetrics ascent:\t" + fontMetrics.ascent)
        Log.e(TAG, "onDraw() fontMetrics bottom:\t" + fontMetrics.bottom)
        Log.e(TAG, "onDraw() fontMetrics descent:\t" + fontMetrics.descent)
        Log.e(TAG, "onDraw() fontMetrics leading:\t" + fontMetrics.leading)
        Log.e(TAG, "onDraw() fontMetrics top:\t" + fontMetrics.top)
    }
}