Android字符串进阶之三：字体属性及丈量（FontMetrics）(转)_Android

Android字符串进阶之三：字体属性及测量（FontMetrics）(转)

转载自:http://mikewang.blog.51cto.com/3826268/871765/

最近的一个模块正好用到字体的相关内容，整理出来。

(一) 字体的几个参数，以Android API文档定义为准，见下图

要点如下：

1. 基准点是baseline

2. Ascent是baseline之上至字符最高处的距离

3. Descent是baseline之下至字符最低处的距离

4. Leading文档说的很含糊，其实是上一行字符的descent到下一行的ascent之间的距离

5. Top指的是指的是最高字符到baseline的值，即ascent的最大值

6. 同上，bottom指的是最下字符到baseline的值，即descent的最大值

Note:网上有很多错误的图，如果有疑问，就参看文档，区分对错。

为了帮助理解，我特此搜索了不同的示意图。对照示意图，会很容易理解FontMetrics的参数。

pic-1

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pic-6

(二) 测试

?1，测试的代码直接使用网上的代码，因为重复着众多，无所给出原始出处，故不注出。

我增加了Bitmap作为输出显示，完整代码如下：

public class FontMetricsDemoActivity extends Activity {     private Canvas canvas;      /** Called when the activity is first created. */     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);                  Paint textPaint = new Paint( Paint.ANTI_ALIAS_FLAG);         textPaint.setTextSize( 55);         textPaint.setColor( Color.WHITE);          // FontMetrics对象         FontMetrics fontMetrics = textPaint.getFontMetrics();         String text = "abcdefghijklmnopqrstu";                            // 计算每一个坐标         float baseX = 0;         float baseY = 100;         float topY = baseY + fontMetrics.top;         float ascentY = baseY + fontMetrics.ascent;         float descentY = baseY + fontMetrics.descent;         float bottomY = baseY + fontMetrics.bottom;         float leading = baseY + fontMetrics.leading;                           Log.d("fontMetrics", "baseX    is:" + 0);         Log.d("fontMetrics", "baseY    is:" + 100);         Log.d("fontMetrics", "topY     is:" + topY);         Log.d("fontMetrics", "ascentY  is:" + ascentY);         Log.d("fontMetrics", "descentY is:" + descentY);         Log.d("fontMetrics", "bottomY  is:" + bottomY);         Log.d("fontMetrics", "leading  is:" + leading);                            Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.fontmetrics);         Bitmap mutableBitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);                  canvas  = new Canvas(mutableBitmap);                            // 绘制文本         canvas.drawText(text, baseX, baseY, textPaint);          // BaseLine描画         Paint baseLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);                  baseLinePaint.setColor( Color.RED);         canvas.drawLine(0, baseY, canvas.getWidth(), baseY, baseLinePaint);          // Base描画         canvas.drawCircle( baseX, baseY, 5, baseLinePaint);          // TopLine描画         Paint topLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);         topLinePaint.setColor( Color.LTGRAY);         canvas.drawLine(0, topY, canvas.getWidth(), topY, topLinePaint);          // AscentLine描画         Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);         ascentLinePaint.setColor( Color.GREEN);         canvas.drawLine(0, ascentY, canvas.getWidth(), ascentY, ascentLinePaint);          // DescentLine描画         Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);         descentLinePaint.setColor( Color.YELLOW);         canvas.drawLine(0, descentY, canvas.getWidth(), descentY, descentLinePaint);          // ButtomLine描画         Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);         bottomLinePaint.setColor( Color.MAGENTA);         canvas.drawLine(0, bottomY, canvas.getWidth(), bottomY, bottomLinePaint);                   ImageView imageView = (ImageView) findViewById(R.id.imageView1);         imageView.setImageBitmap(mutableBitmap);              } }

?log显示如下：

Note1：注意到各个数值都是整数，这是建立在baseY=100的情况下，去掉baseY,重新运行代码，log如下：

Note2: 参照线为baseline，即baseline=0的情况下，其他各线的数值。leading = 0,即行间距=0

2，以上是根据paint设置，获取相关的FontMetrics属性，并且只绘制了一行字符串，我们猜想，如果是多行，是否可以获得行间距leanding，代码如下：

//test_multiply_lines         TextView textView = (TextView) findViewById(R.id.textView1);         String textMultiLines = "abcdefghijklmnopqrstuabcdefghijklmnopqrstuabcdefghijklmnopqrstuabcdefghijklmnopqrstuabcdefghijklmnopqrstu";         textView.setTextSize(55);         textView.setText(textMultiLines);                  FontMetrics fontMetrics2 = textView.getPaint().getFontMetrics();                            // 计算每一个坐标          float topY = fontMetrics2.top;         float ascentY = fontMetrics2.ascent;         float descentY =  fontMetrics2.descent;         float bottomY = fontMetrics2.bottom;         float leading =  fontMetrics2.leading;                            Log.d("fontMetrics", "topY     is:" + topY);         Log.d("fontMetrics", "ascentY  is:" + ascentY);         Log.d("fontMetrics", "descentY is:" + descentY);         Log.d("fontMetrics", "bottomY  is:" + bottomY);         Log.d("fontMetrics", "leading  is:" + leading);

log如下：

Note：显然，即使是多行的情况下，仍不能获得leading。

3，如果text是单行，获得各个属性将会怎样，代码如下：

String text = "abcdefghijklmnopqrstu";         TextView textView = (TextView) findViewById(R.id.textView1);         textView.setTextSize(55);         textView.setText(text);                  FontMetrics fontMetrics = textView.getPaint().getFontMetrics();          // 计算每一个坐标         float baseX = 0;         float baseY = 100;         float topY = baseY + fontMetrics.top;         float ascentY = baseY + fontMetrics.ascent;         float descentY = baseY + fontMetrics.descent;         float bottomY = baseY + fontMetrics.bottom;         float leading =  fontMetrics.leading;                            Log.d("fontMetrics", "topY     is:" + fontMetrics.top);         Log.d("fontMetrics", "ascentY  is:" + fontMetrics.ascent);         Log.d("fontMetrics", "descentY is:" + fontMetrics.descent);         Log.d("fontMetrics", "bottomY  is:" + fontMetrics.bottom);         Log.d("fontMetrics", "leading  is:" + fontMetrics.leading);

log如下图所示：

Note：与多行获得的属性都相同。

结论：

A:虽然paint和textView所设置的textSize均为55，且为相同的字符串，但是两个获得的FontMetrics属性值并不相同。但是，我们发现，做除法之后，均为1.5倍关系。做出猜测，即Paint下，为mdpi对应的size，而TextView的size已经关联到了显示屏幕本身的320dip。所以获得属性值均为整1.5倍数

B:各种情况下，均未获得leading值。

另转?androd之绘制文本（FontMetrics）:

Canvas 作为绘制文本时，使用FontMetrics对象，计算位置的坐标。

它的思路和java.awt.FontMetrics的基本相同。

FontMetrics对象

它以四个基本坐标为基准，分别为：

?FontMetrics.top
?FontMetrics.ascent
?FontMetrics.descent
?FontMetrics.bottom

该图片将如下(代码画出来的图)

Paint textPaint = new Paint( Paint.ANTI_ALIAS_FLAG);  textPaint.setTextSize( 35);  textPaint.setColor( Color.WHITE);    // FontMetrics对象  FontMetrics fontMetrics = textPaint.getFontMetrics();    String text = "abcdefghijklmnopqrstu";    // 计算每一个坐标  float baseX = 0;  float baseY = 100;  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, textPaint);    // BaseLine描画  Paint baseLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);>  baseLinePaint.setColor( Color.RED);  canvas.drawLine(0, baseY, getWidth(), baseY, baseLinePaint);    // Base描画  canvas.drawCircle( baseX, baseY, 5, baseLinePaint);    // TopLine描画  Paint topLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);  topLinePaint.setColor( Color.LTGRAY);  canvas.drawLine(0, topY, getWidth(), topY, topLinePaint);    // AscentLine描画  Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);  ascentLinePaint.setColor( Color.GREEN);  canvas.drawLine(0, ascentY, getWidth(), ascentY, ascentLinePaint);    // DescentLine描画  Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);  descentLinePaint.setColor( Color.YELLOW);  canvas.drawLine(0, descentY, getWidth(), descentY, descentLinePaint);    // ButtomLine描画  Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);  bottomLinePaint.setColor( Color.MAGENTA);  canvas.drawLine(0, bottomY, getWidth(), bottomY, bottomLinePaint);