官方文档:
public void drawText (String text, float x, float y, Paint paint)
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)
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方案一:以baseline为基准
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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:
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);
**
方案二:以目标矩形为参照物
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Canvas绘图,drawText里的origin是以baseline为基准的,直接以目标矩形的bottom传进drawText,字符位置会偏下。这样写代码:
@Override
public void onDraw (Canvas canvas) {
Rect targetRect = new Rect(50, 50, 1000, 200);
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStrokeWidth(3);
paint.setTextSize(80);
String testString = "测试:ijkJQKA:1234";
paint.setColor(Color.CYAN);
canvas.drawRect(targetRect, paint);
paint.setColor(Color.RED);
canvas.drawText(testString, targetRect.left, targetRect.bottom, paint);
}
首先自己动手做实验,自己定一个baseline,然后把文字画上去,再画上FontMetrics的几条线。FontMetrics里是字体图样的信息,有float型和int型的版本,都可以从Paint中获取。它的每个成员数值都是以baseline为基准计算的,所以负值表示在baseline之上。实验代码:
@Override
public void onDraw (Canvas canvas) {
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStrokeWidth(3);
paint.setTextSize(80);
FontMetricsInt fmi = paint.getFontMetricsInt();
String testString = "测试:ijkJQKA:1234";
Rect bounds1 = new Rect();
paint.getTextBounds("测", 0, 1, bounds1);
Rect bounds2 = new Rect();
paint.getTextBounds("测试:ijk", 0, 6, bounds2);
// 随意设一个位置作为baseline
int x = 200;
int y = 400;
// 把testString画在baseline上
canvas.drawText(testString, x, y, paint);
// bounds1
paint.setStyle(Style.STROKE); // 画空心矩形
canvas.save();
canvas.translate(x, y); // 注意这里有translate。getTextBounds得到的矩形也是以baseline为基准的
paint.setColor(Color.GREEN);
canvas.drawRect(bounds1, paint);
canvas.restore();
// bounds2
canvas.save();
paint.setColor(Color.MAGENTA);
canvas.translate(x, y);
canvas.drawRect(bounds2, paint);
canvas.restore();
// baseline
paint.setColor(Color.RED);
canvas.drawLine(x, y, 1024, y, paint);
// ascent
paint.setColor(Color.YELLOW);
canvas.drawLine(x, y+fmi.ascent, 1024, y+fmi.ascent, paint);
// descent
paint.setColor(Color.BLUE);
canvas.drawLine(x, y+fmi.descent, 1024, y+fmi.descent, paint);
// top
paint.setColor(Color.DKGRAY);
canvas.drawLine(x, y+fmi.top, 1024, y+fmi.top, paint);
// bottom
paint.setColor(Color.GREEN);
canvas.drawLine(x, y+fmi.bottom, 1024, y+fmi.bottom, paint);
}
红线是baseline,最上面的灰线是FontMetrics.top,最下面的绿线是FontMetrics.bottom。(绿色的bottom和蓝色的descent非常接近)
从图中可知,字符本身是在灰线和绿线之间居中的,知道这个就好办了。网上说的使用paint.getTextBounds的方法都不靠谱,可以看到对一个“测”字和6个字得到的bounds是不同的,图中的矩形能很好地表示这个函数得到的是字符的边界,而不是字体的边界。
FontMetrics.top的数值是个负数,其绝对值就是字体绘制边界到baseline的距离。
所以如果是把文字画在 FontMetrics高度的矩形中, drawText就应该传入 -FontMetrics.top。
要画在targetRect的居中位置,baseline的计算公式就是:
targetRect.centerY() - (FontMetrics.bottom - FontMetrics.top) / 2 - FontMetrics.top
优化后即:
(targetRect.bottom + targetRect.top - fontMetrics.bottom - fontMetrics.top) / 2
所以最开始的代码应该改成(顺便加入水平居中):
@Override
public void onDraw (Canvas canvas) {
Rect targetRect = new Rect(50, 50, 1000, 200);
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStrokeWidth(3);
paint.setTextSize(80);
String testString = "测试:ijkJQKA:1234";
paint.setColor(Color.CYAN);
canvas.drawRect(targetRect, paint);
paint.setColor(Color.RED);
FontMetricsInt fontMetrics = paint.getFontMetricsInt();
// 转载请注明出处:http://blog.csdn.net/hursing
int baseline = (targetRect.bottom + targetRect.top - fontMetrics.bottom - fontMetrics.top) / 2;
// 下面这行是实现水平居中,drawText对应改为传入targetRect.centerX()
paint.setTextAlign(Paint.Align.CENTER);
canvas.drawText(testString, targetRect.centerX(), baseline, paint);
}
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方案三:以某个点为基准居中
**
float offset = Math.abs(textPaint.descent() + textPaint.ascent()) / 2
canvas.drawText(str, x, y + offset, paint);
前两种解决方案来自下面两篇博客
http://blog.youkuaiyun.com/hursing
http://blog.youkuaiyun.com/lvxiangan/article/details/8540774