Re: How to detect if mouse pointer is over a type of object.

RichT wrote:
Hi all once again :)

This question is really of two parts.

part one
I am constructing an arrow using a line as the tail of the arrow and a filled polygon for the arrow head which is an array of three pairs of
x, y points used to construct the arrow.

an example of this arrow may look something like this
|\
-----------------| \
|/

So my first question is how can I create some sort of bounding shape around this shape so that when I click on any part of the arrow it becomes selected, or if this will prove too hard just clicking the arrow head to select the shape.

What I ideally would like is once the mouse pointer is clicked on the arrow little selection handles would be drawn at the x0 of the line segment and at each point of the points of the arrow head perhaps using a 3x3 filled rectangle as each handle.

I think I know how to create and position these handles as I have a reference to the necessary x0,y0,x1,y1 points of the arrow tail and each of the vertices of the arrowhead.

Part two is related I believe to part one as once I have figured out how to bound the arrow shape, I want to be able to detect if I click on this shape with the left or right mouse button.

I believe I can do this by using the if rectangle.contains(Point) Method???? but not too sure?, a better way if it exists would be to check if the object under the mouse pointer when clicked is a type of a class.

I will include the code for constructing the arrow below, in case my explanation is not too clear.

Hope someone can help or point me in the right direction

Rich

Code below.

import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class ArrowPanel extends JPanel {

FixedHeadArrow arrow;
ArrayList<FixedHeadArrow> arrowList = new ArrayList<FixedHeadArrow>();

public ArrowPanel() {
addMouseListener(new MouseAdapter() {

@Override
public void mousePressed(MouseEvent e) {
arrow = new FixedHeadArrow();
arrow.x0 = e.getX();
arrow.y0 = e.getY();
arrow.x1 = arrow.x0;
arrow.y1 = arrow.y0;
arrowList.add(arrow);
}

@Override
public void mouseReleased(MouseEvent e) {
arrow.x1 = e.getX();
arrow.y1 = e.getY();
}
});
addMouseMotionListener(new MouseMotionAdapter() {
@Override
public void mouseDragged(MouseEvent e) {
arrow.x1 = e.getX();
arrow.y1 = e.getY();
repaint();
}
});
}

@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
for (FixedHeadArrow fha : arrowList) {
fha.draw(g);
}
}

public static void main(String[] args) {
ArrowPanel arrowPanel = new ArrowPanel();
JFrame f = new JFrame();
f.add(arrowPanel);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(400, 400);
f.setLocationRelativeTo(null); // centre
f.setVisible(true);
}

public class FixedHeadArrow {
private static final double HEAD_LENGTH = 10;
private static final double HEAD_WIDTH = 5; // actually half the width
private static final double TAN = HEAD_WIDTH / HEAD_LENGTH;
int x0;
int y0;
int x1;
int y1;
private int xHeadPoints[] = new int[3];
private int yHeadPoints[] = new int[3];

public void draw(Graphics g) {
int dx = x1 - x0;
int dy = y1 - y0;
double lineLength = Math.sqrt(dx * dx + dy * dy);
double ratio = HEAD_LENGTH / lineLength;
xHeadPoints[0] = x0 + (int) Math.round((1 - ratio) * dx + (ratio * dy) * TAN);
yHeadPoints[0] = y0 + (int) Math.round((1 - ratio) * dy - (ratio * dx) * TAN);
xHeadPoints[1] = x0 + (int) Math.round((1 - ratio) * dx - (ratio * dy) * TAN);
yHeadPoints[1] = y0 + (int) Math.round((1 - ratio) * dy + (ratio * dx) * TAN);
// 3rd point of arrow head is line end
xHeadPoints[2] = x1;
yHeadPoints[2] = y1;
g.drawLine(x0, y0, x1, y1);
g.fillPolygon(xHeadPoints, yHeadPoints, 3);
for (int x = 0; x < xHeadPoints.length; ++x) {
System.out.println("x Point: " + xHeadPoints[x] + " y Points: " + yHeadPoints[x]);
}
}
}
}

Here is a simple example, when you put the mouse over the shape it changes color. If you press the mouse when you are on the shape it changes to a unfilled polygon.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test7 extends JPanel {
int x[] = { 80,100,81,81,80,80,60,80 };
int y[] = { 40,60,60,120,120,60,60,40 };
Polygon poly = new Polygon(x,y,x.length);
boolean fillFlag = true;
boolean overFlag;


public test7() {
setPreferredSize(new Dimension(400,300));

// if mouse is clicked on poly, toggle fill flag
addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent me) {
if (poly.contains(me.getX(),me.getY())) {
fillFlag = !fillFlag;
repaint();
}
}
});

// if mouse is over poly change its color
addMouseMotionListener(new MouseAdapter() {
public void mouseMoved(MouseEvent me) {
if (poly.contains(me.getX(),me.getY())) {
overFlag = true;
} else
overFlag = false;
repaint();
}
});
}

public void paintComponent(Graphics g2D) {
Graphics2D g = (Graphics2D)g2D;

g.setColor(Color.WHITE);
g.fillRect(0,0,getWidth(),getHeight());

if (overFlag)
g.setColor(Color.GREEN);
else
g.setColor(Color.RED);

if (fillFlag)
g.fillPolygon(poly);
else
g.drawPolygon(poly);
}

public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
test7 t7 = new test7();
f.add(t7,BorderLayout.CENTER);
f.pack();
f.setVisible(true);
}
});
}
}

--

Knute Johnson
email s/nospam/knute2008/

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