关于Android Canvas.drawText方法中的坐标参数的正确解释

canvas.drawText("www.jcodecraeer.com", x, y, paint);  x和y参数是指定字符串中心的坐标吗？还是左上角的坐标？这个问题的直观印象应该是左上角的坐标，但是安卓的处理有点另类，我都怀疑安卓的设计者是不是脑壳有问题了。
x默认是‘www.jcodecraeer.com’这个字符串的左边在屏幕的位置，如果设置了paint.setTextAlign(Paint.Align.CENTER);那就是字符的中心，y是指定这个字符baseline在屏幕上的位置。

API的解释：

public void drawText (String text, float x, float y, Paint paint)
Since: API Level 1 Draw the text, with origin at (x,y), using the specified paint.
The origin is interpreted based on the Align setting in the paint.

起始点的具体位置决定于paint的align设置。
Parameters
text The text to be drawn
x The x-coordinate of the origin of the text being drawn 
y The y-coordinate of the origin of the text being drawn 
paint The paint used for the text (e.g. color, size, style)

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

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);

drawText画字符串是baseline对齐的。所以要特别注意这点，不然画文字可能画到其它地方而误以为没有画出来。

如果baseline对齐的话：底端的Y坐标是：(行高-字体高度)/2+字体高度 ，但是字符串并不居中，经过测试如果：(行高-字体高度)/2+字体高度-6 ，就稍微居中了一点。 以上的方法只是一个取巧的做法，网上也没有找到设置文字居中的方法。

按上面办法会有误差。加上那段距离应该就行了:

1 2 3 4 5

FontMetrics fontMetrics = mPaint.getFontMetrics(); float fontTotalHeight = fontMetrics.bottom - fontMetrics.top; float offY = fontTotalHeight / 2 - fontMetrics.bottom; float newY = baseY + offY; canvas.drawText(text, baseX, newY, paint);