Android字符串进阶之三：字体属性及测量（FontMetrics）

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

 

pic-2

 

pic-3

 

pic-4

 

pic-5

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);