[Android]Android字体高度的研究

android自定义View绘制的时候，会有很多情况下要与字体打交道，涉及到字体宽度、高度的时候要特别注意一下几个概念，见图：

baseLine：一行文字的底线。

Ascent：字符顶部到baseLine的距离。

Descent：字符底部到baseLine的距离。

Leading：字符行间距。

public class TestOnDraw extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);MyView v = new MyView(this);this.setContentView(v);}}class MyView extends View{public MyView(Context context) {super(context);}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);Paint p = new Paint();p.setColor(Color.WHITE);p.setTextSize(50);p.setAntiAlias(true);FontMetrics fm = p.getFontMetrics();System.out.println("top = "+ fm.top);System.out.println("ascent = "+ fm.ascent);System.out.println("descent = "+ fm.descent);System.out.println("bottom = "+ fm.bottom);System.out.println("leading = "+ fm.leading);        int textHeight = (int) (Math.ceil(fm.descent - fm.ascent) + 2);        System.out.println("textHeight = "  + textHeight);                float width =500;        float baseline = 100f;        float offsetAscent = baseline + fm.ascent;        float offsetDescent = baseline +fm.descent;        float offsetTop = baseline + fm.top;        float offsetBottom = baseline + fm.bottom;                canvas.drawText("中国 bp Android", 0, baseline, p);canvas.drawLine(0, baseline, width, baseline, p);//baselinecanvas.drawLine(0, offsetAscent, width, offsetAscent, p);//ascentcanvas.drawLine(0, offsetDescent, width, offsetDescent, p);//descentcanvas.drawLine(0, offsetTop, width, offsetTop, p);//topcanvas.drawLine(0, offsetBotton, width, offsetBottom, p);//bottom}}

运行效果：

[Android]Android字体高度的研究

这是程序的输出结果：

得出结论： canvas drawText() 的startX是从左下角的baseline的底线开始绘画的，如果我们要得到字体的高度需要关注descent - ascent (ascent线在baseline上面，所以是负数)

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