Android使用FontMetrics对象计算位置坐标

canvas绘制文本时，使用fontmetrics对象，计算位置的坐标。

public static class fontmetrics {
  /**
   * the maximum distance above the baseline for the tallest glyph in 
   * the font at a given text size.
   */
  public float  top;
  /**
   * the recommended distance above the baseline for singled spaced text.
   */
  public float  ascent;
  /**
   * the recommended distance below the baseline for singled spaced text.
   */
  public float  descent;
  /**
   * the maximum distance below the baseline for the lowest glyph in 
   * the font at a given text size.
   */
  public float  bottom;
  /**
   * the recommended additional space to add between lines of text.
   */
  public float  leading;
}

它的各基准线可以参考下图：

上图其实是通过代码画出来的，具体代码如下：

/** 绘制fontmetrics对象的各种线 */
mpaint.reset();
mpaint.setcolor(color.white);
mpaint.settextsize(80);
// fontmetrics对象
fontmetrics fontmetrics = mpaint.getfontmetrics();
string text = "abcdefg";
// 计算每一个坐标
float textwidth = mpaint.measuretext(text);
float basex = 30;
float basey = 700;
float topy = basey + fontmetrics.top;
float ascenty = basey + fontmetrics.ascent;
float descenty = basey + fontmetrics.descent;
float bottomy = basey + fontmetrics.bottom;
// 绘制文本
canvas.drawtext(text, basex, basey, mpaint);
// baseline描画
mpaint.setcolor(color.red);
canvas.drawline(basex, basey, basex + textwidth, basey, mpaint);
mpaint.settextsize(20);
canvas.drawtext("base", basex + textwidth, basey, mpaint);
// base描画
canvas.drawcircle(basex, basey, 5, mpaint);
// topline描画
mpaint.setcolor(color.ltgray);
canvas.drawline(basex, topy, basex + textwidth, topy, mpaint);
canvas.drawtext("top", basex + textwidth, topy, mpaint);
// ascentline描画
mpaint.setcolor(color.green);
canvas.drawline(basex, ascenty, basex + textwidth, ascenty, mpaint);
canvas.drawtext("ascent", basex + textwidth, ascenty + 10, mpaint);
// descentline描画
mpaint.setcolor(color.yellow);
canvas.drawline(basex, descenty, basex + textwidth, descenty, mpaint);
canvas.drawtext("descent", basex + textwidth, descenty, mpaint);
// buttomline描画
mpaint.setcolor(color.magenta);
canvas.drawline(basex, bottomy, basex + textwidth, bottomy, mpaint);
canvas.drawtext("buttom", basex + textwidth, bottomy + 10, mpaint);

相信通过以上程序，能够很好的理解topline，buttomline，baseline，ascentline，descentline。
另外：paint类有两个方法

/**
 * return the distance above (negative) the baseline (ascent) based on the
 * current typeface and text size.
 *
 * @return the distance above (negative) the baseline (ascent) based on the
 *     current typeface and text size.
 */
public native float ascent();
 
/**
 * return the distance below (positive) the baseline (descent) based on the
 * current typeface and text size.
 *
 * @return the distance below (positive) the baseline (descent) based on
 *     the current typeface and text size.
 */
public native float descent();

ascent()：the distance above the baseline（baseline以上的height）
descent()：the distance below the baseline（baseline以下的height）

所以ascent() + descent() 可以看成文字的height。

到此为止，怎么获取文字的height和width都已经揭晓了：

获取height ： mpaint.ascent() + mpaint.descent()

获取width ： mpaint.measuretext(text)

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。