canvas.drawText()文字居中和靠左

• 文字居中：

paint.setTextAlign(Paint.Align.Center);
canvas.drawText(txt,viewW/2.0f,0f,paint);

• 文字靠左

paint.setTextAlign(Paint.Align.Left);
canvas.drawText(txt,0f,0f,paint);

参考：Android Canvas的drawText()和文字居中方案