Canvas&Paint[]Paint：drawText位置

【参考链接】

drawText()详解http://blog.****.net/harvic880925/article/details/50423762

在绘制文本时，drawText要指定(x，y)坐标。但是这个(x，y)坐标并不是文本矩形的左上角坐标，默认x是文本的最左边，y是文本的baseline.

并且这里可以看到文本左侧并没有完全靠齐，这其实也是后面getTextBound()和measureText()的差距

x

根据paint. setTextAlign()的设置，将TextAlign线放置到x坐标上

可选的值有PAINT.ALIGN.LEFT、PAINT.ALIGN.RIGHT、PAINT.ALIGN.CENTER

Canvas&Paint[]Paint：drawText位置

y

设置的值作为字符串的baseline线。

对于一个文本，一共有5条横线，可以通过paint.getFontMatrics()得到其余4条线相对于baseline线的偏移

paintAll.setTextSize(80);

//获取文本的其他线到baseline的距离
paintAll.setColor(Color.parseColor("#0000FF"));
Paint.FontMetricsfontMetrics = paintAll.getFontMetrics();//这个要在设置完setTextSize()以后调用
canvas.drawLine(0, yBaseline+fontMetrics.ascent, 800, yBaseline+fontMetrics.ascent, paintAll);
canvas.drawLine(0, yBaseline+fontMetrics.descent, 800, yBaseline+fontMetrics.descent, paintAll);
canvas.drawLine(0, yBaseline+fontMetrics.top, 800, yBaseline+fontMetrics.top, paintAll);
canvas.drawLine(0, yBaseline+fontMetrics.bottom, 800, yBaseline+fontMetrics.bottom, paintAll);

//绘制文本
paintAll.setColor(Color.parseColor("#000000"));
paintAll.setTextAlign(Paint.Align.CENTER);
canvas.drawText(text, 300, yBaseline, paintAll);

Canvas&Paint[]Paint：drawText位置

所以如果要将文本以(x,y)点为左上角进行配置，x需要设置成x+ascent

如何在绘制之前，得到文本的长宽信息呢

Paint提供了两个方法getTextBounds()和measureText()，这两个方法也是需要在setTextSize()以后才有效

getTextBounds()用于获取文本的外包矩形，但是其值是相对于x=0/LEFT，y=0/baseline时的

measureText()用于获取文本的测量宽度，这个宽度才是绘制时使用的宽度，跟上面的外包矩形的宽度并不一样（要稍微大一些）

private String text="shadowfaxg";
private int yBaseline=300;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    Bitmap bmp=Bitmap.createBitmap(800, 800, Bitmap.Config.ARGB_8888);
    Canvas canvas=new Canvas(bmp);

    //默认画笔
    Paint paintAll=new Paint();
    paintAll.setAlpha(255);//不透明度//完全不透明
    paintAll.setAntiAlias(true);
    paintAll.setColor(Color.parseColor("#000000"));//黑色//默认就是黑色
    paintAll.setStyle(Paint.Style.FILL);

    paintAll.setColor(Color.parseColor("#FF0000"));
    canvas.drawLine(yBaseline, 0, yBaseline, 800, paintAll);
    canvas.drawLine(0, yBaseline, 800, yBaseline, paintAll);

    paintAll.setTextSize(80);

    //获取文本的其他线到baseline的距离
    paintAll.setColor(Color.parseColor("#0000FF"));
    Paint.FontMetrics fontMetrics =paintAll.getFontMetrics();//这个要在设置完setTextSize()以后调用
    canvas.drawLine(0, yBaseline+fontMetrics.ascent, 800, yBaseline+fontMetrics.ascent, paintAll);
    canvas.drawLine(0, yBaseline+fontMetrics.descent, 800, yBaseline+fontMetrics.descent, paintAll);
    canvas.drawLine(0, yBaseline+fontMetrics.top, 800, yBaseline+fontMetrics.top, paintAll);
    canvas.drawLine(0, yBaseline+fontMetrics.bottom, 800, yBaseline+fontMetrics.bottom, paintAll);

    //getTextBounds()
    Rect rect=new Rect();
    paintAll.getTextBounds(text, 0, text.length(), rect);
    int width1=(rect.right-rect.left);
    Log.e("shadowfaxghh", "width1="+width1);

    //measureText()//稍微大一些
    float width2 = paintAll.measureText(text);
    Log.e("shadowfaxghh", "width2="+width2);

    int offset = 300;

    paintAll.setColor(Color.GREEN);
    canvas.drawRect(offset, rect.top+yBaseline, width2+offset, rect.bottom+yBaseline, paintAll);

    paintAll.setColor(Color.MAGENTA);
    canvas.drawRect(rect.left, rect.top, rect.right, rect.bottom, paintAll);
    canvas.drawRect(rect.left+offset, rect.top+yBaseline, rect.right+offset, rect.bottom+yBaseline, paintAll);

    //绘制文本
    paintAll.setColor(Color.parseColor("#000000"));
    paintAll.setTextAlign(Paint.Align.LEFT);
    canvas.drawText(text, 300, yBaseline, paintAll);

    ImageView iv = (ImageView)findViewById(R.id.iv);
    iv.setImageBitmap(bmp);
}

Canvas&Paint[]Paint：drawText位置

Canvas&Paint[]Paint：drawText位置

x

y

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