trouble with: FontMetrics.getStringBounds() and Rectangle.contains()

[rippon]

Ultimately, I want to have strings moving around a space (for which I presume JPanel is best) as targets for the user to click on. A string will occupy a rectangular space and my code will need to determine whether the user clicked inside that rectangle, i.e. hit the target.

Towards that end, I'm just trying to write some simple code to confirm that I can indeed correctly identify a point as being within a rectangle. My code draws a string ("hallo world") at (x,y)-position (50,50). Therefore, the point (51,51) should definitely (I think) lie *within* the rectangle bounding my string. But my code produces the output "No!" when it should be "Yes!".

Please help. Thanks.

       public void paintComponent(Graphics g){
            Rectangle stringBounds;
            
            super.paintComponent(g);
            g.setFont(myFont);
            myGraphics = g;
            myFontMetrics = g.getFontMetrics();
            stringToDraw = "hallo world";
            myGraphics.drawString(stringToDraw, 50, 50);
            stringBounds = myFontMetrics.
                    getStringBounds(stringToDraw, myGraphics).getBounds();
            if (stringBounds.contains(new Point(51,51))){
                messageBox.setText("Yes!");
            }
            else  messageBox.setText("No!");
        }

[DarrylBurke]

Your assumptions are wrong. The Graphics reference uses the String bounds from FontMetrics to lay out the text. The FontMetrics instance has no clue that the String was translated to [50, 50] by the Graphics drawString method.

It rather looks like you're a victim of a very common but erroneous interpretation of a Graphics object as a painting surface. Try thinking of the Graphics as a brush or pen that paints on a surface -- which is the GraphicsContext.

And since this topic is related to Java 2D rather than Swing, I shall move it there.

db

[rippon]

Thanks. I'd be very grateful if you (or anyone) could show me some code that would achieve what I'm trying to.

[spring]

you "hello world" shoud in that place, (50,50) is the baseline of the str, the Rectangle of "hello world" on Container is (50, 50+stringBounds.getY(),stringBounds.getWidth(),str ingBounds.getHeight()), stringBounds.getY() is negative。

[ozzyman]

Wouldn't it be easier if you knew the text position before-hand to keep track of it and check if it intersects with a mouse click?

1. Create your font

Font f = new Font("Tahoma", Font.BOLD, 24);

2. Create glyph vectors from the some text String

GlyphVector gv = f.createGlyphVector(getFontMetrics(f).getFontRende rContext(), "Some text message");

3. Convert glyph vectors to a shape

Shape s = gv.getOutline();

4. Throw section 2-3 into a method you can call back to return the shape

private Font f = new Font(...);

public Shape getShapeFromString(String message) {
    //methods 2-3;
    ...
    return s;
}

5. Create a new method to test whether the mouse intersected with a shape

public boolean hitMessage(Shape s, int mouseX, int mouseY) {
    //allow some in-accuracy by converting the point mouseX, mouseY into a 10 by 10 Rectangle2D
    Rectangle2D r2d = new Rectangle2D.Double(mouseX-5, mouseY-5, 10, 10);
    return s.intersects(r2d);
}

I think the rest is fairly simple for you.

[camickr]

Just use a JLabel and add the MouseListener to the label. You move the label around the screen by invoking setLocation().