Android中FontMetrics對象的各種基准線

Android中FontMetrics對象的各種基准線(以及怎麼獲取文字的width和height) 。

Canvas 作為繪制文本時，使用FontMetrics對象，計算位置的坐標。

1. public static class FontMetrics {
2. /**
3. * The maximum distance above the baseline for the tallest glyph in
4. * the font at a given text size.
5. */
6. public float top;
7. /**
8. * The recommended distance above the baseline for singled spaced text.
9. */
10. public float ascent;
11. /**
12. * The recommended distance below the baseline for singled spaced text.
13. */
14. public float descent;
15. /**
16. * The maximum distance below the baseline for the lowest glyph in
17. * the font at a given text size.
18. */
19. public float bottom;
20. /**
21. * The recommended additional space to add between lines of text.
22. */
23. public float leading;
24. }

它的各基准線可以參考下圖：

上圖其實是通過代碼畫出來的，具體代碼如下：

1. /** 繪制FontMetrics對象的各種線 */
2. mPaint.reset();
3. mPaint.setColor(Color.WHITE);
4. mPaint.setTextSize(80);
5. // FontMetrics對象
6. FontMetrics fontMetrics = mPaint.getFontMetrics();
7. String text = "abcdefg";
8. // 計算每一個坐標
9. float textWidth = mPaint.measureText(text);
10. float baseX = 30;
11. float baseY = 700;
12. float topY = baseY + fontMetrics.top;
13. float ascentY = baseY + fontMetrics.ascent;
14. float descentY = baseY + fontMetrics.descent;
15. float bottomY = baseY + fontMetrics.bottom;
16. // 繪制文本
17. canvas.drawText(text, baseX, baseY, mPaint);
18. // BaseLine描畫
19. mPaint.setColor(Color.RED);
20. canvas.drawLine(baseX, baseY, baseX + textWidth, baseY, mPaint);
21. mPaint.setTextSize(20);
22. canvas.drawText("base", baseX + textWidth, baseY, mPaint);
23. // Base描畫
24. canvas.drawCircle(baseX, baseY, 5, mPaint);
25. // TopLine描畫
26. mPaint.setColor(Color.LTGRAY);
27. canvas.drawLine(baseX, topY, baseX + textWidth, topY, mPaint);
28. canvas.drawText("top", baseX + textWidth, topY, mPaint);
29. // AscentLine描畫
30. mPaint.setColor(Color.GREEN);
31. canvas.drawLine(baseX, ascentY, baseX + textWidth, ascentY, mPaint);
32. canvas.drawText("ascent", baseX + textWidth, ascentY + 10, mPaint);
33. // DescentLine描畫
34. mPaint.setColor(Color.YELLOW);
35. canvas.drawLine(baseX, descentY, baseX + textWidth, descentY, mPaint);
36. canvas.drawText("descent", baseX + textWidth, descentY, mPaint);
37. // ButtomLine描畫
38. mPaint.setColor(Color.MAGENTA);
39. canvas.drawLine(baseX, bottomY, baseX + textWidth, bottomY, mPaint);
40. canvas.drawText("buttom", baseX + textWidth, bottomY + 10, mPaint);

相信通過以上程序，能夠很好的理解topLine，buttomLine，baseLine，ascentLine，descentLine。

另外：Paint類有兩個方法

1. /**
2. * Return the distance above (negative) the baseline (ascent) based on the
3. * current typeface and text size.
4. *
5. * @return the distance above (negative) the baseline (ascent) based on the
6. * current typeface and text size.
7. */
8. public native float ascent();
10. /**
11. * Return the distance below (positive) the baseline (descent) based on the
12. * current typeface and text size.
13. *
14. * @return the distance below (positive) the baseline (descent) based on
15. * the current typeface and text size.
16. */
17. 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。

到此為止，怎麼獲取文字的height和width都已經揭曉了：

獲取height ： mPaint.ascent() + mPaint.descent()

獲取width ： mPaint.measureText(text)