圆圈中心的文字

Question

There is a circle (planet), drawn through fillOval(). I need to write the text (number) on the circle, so that it must be always aligned exactly in the center. There is a center of the circle and its radius. I understand that I need to calculate the width and length of the text (tried by getStringBounds), but does not work correctly.

protected void paintComponent(Graphics g){
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g.create();
    for (Planet planet : planets) {
        g2d.setColor(planet.getColor());
        g2d.fillOval((int) planet.getX() - planet.getRadius(), (int) planet.getY() - planet.getRadius(),
        planet.getRadius() * 2, planet.getRadius() * 2);
        g.setFont(new Font("Serif", Font.PLAIN, 20));
        g.setColor(Color.black);
        String s = String.valueOf(250);
        FontMetrics fm = g.getFontMetrics();
        double textWidth = fm.getStringBounds(s, g).getWidth();
        g.setColor(Color.white);
        g.drawString(s, (int) ((int) planet.getX() - textWidth/2), ((int) planet.getY() + fm.getMaxAscent() / 2));}}

Answer 1

You're using planet.getX()-planet.getRadius() and planet.getY() - planet.getRadius() to calculate your centered point of the circle.

Then you have to add the Text you want to paint at the centered position, which is calculated

planet.getX() - planet.getRadius() - textWidth/2 //or centered point - textWidth/2

which is your x-coordinate and

planet.getY() - planet.getRadius() + fm.getMaxAscent() / 2 //or centered point + fm.getMaxAscent()/2

which will be the y-coordinate.

But you are using planet.getX() - textWidth/2

This origin point has to be the center of the circle, not planet.getX()

Answer 2

In the past I've had to use both the ascent/descent values to calculate actual font height and it looks like you're only using ascent. Something to consider: not all strings will have the same max ascent/descent for a given font, so while the string "Dojo" may appear to be properly vertically aligned, the strings "cujo" and "coco" might not.

Another suggestion: instead of calculating the half-width of your text and using that to offset your drawing starting position, why not just center justify the text?