Drawing Program

When the user clicks the mouse, a new oval is created on the display. The user can drag around any oval.

import java.awt.*;
import objectdraw.*;
/*
 * A simple drawing program that allows the user to place dots,
 * drag them around and delete them by dragging them to the trash.
 */
public class DrawingProgram extends WindowController {

    // Size of shape to draw
    private static final int SIZE = 20;

    // The variable to hold the last shape created
    private FilledOval selectedShape;
    
    // All the shapes added so far
    private ShapeCollection shapes = new ShapeCollection();

    // Used to support the usual dragging algorithm
    private boolean dragging;
    private Location lastMouse;
    
    // Used to generate random colors
    private RandomIntGenerator colorGen = new RandomIntGenerator (0, 255);

    /**
     * When the user clicks the mouse, draw a small filled oval.
     * @param point the location where the user clicked
     */
    public void onMouseClick (Location point) {
        // Create a shape
        selectedShape = new FilledOval(point, SIZE, SIZE, canvas);
        Color shapeColor = new Color (colorGen.nextValue(), colorGen.nextValue(), colorGen.nextValue());
        selectedShape.setColor (shapeColor);
        shapes.addShape (selectedShape);
    }

    /* 
     * Select the object pressed on and start a drag of that object
     * @param loc where the user pressed the mouse button down
     */
    public void onMousePress(Location loc) {
        // Select the new object and initialize the drag.
        selectedShape = shapes.getShapeAt (loc);
        if (selectedShape != null) {
            dragging = true;
            lastMouse = loc;
        }
    }
    
    /* 
     * Drag the shape with the mouse. 
     * @param loc where the mouse is 
     */
    public void onMouseDrag(Location loc) {
        if (dragging) {
            // Move the shape and the selection border around the shape
            selectedShape.move(loc.getX() - lastMouse.getX(), loc.getY() - lastMouse.getY());
            lastMouse = loc;
        }
    }

    /* 
     * Stop a drag.  If the user dragged a shape to the trash, remove the shape
     * @param point where the mouse is.
     */
    public void onMouseRelease(Location point) {
        dragging = false;
    }

}

import objectdraw.*;
/**
 * A collection of shapes
 * 
 * @author Barbara Lerner 
 * @version December 3, 2007
 */
public class ShapeCollection
{
    // The maximum number of shapes in the collection
    private static final int MAX_SHAPES = 200;
    
    // The actual shapes
    private FilledOval[] shapes;
    
    // The number of shapes currently in the collection
    private int numShapes;
    
    /**
     * Create a new, empty collection
     */
    public ShapeCollection () {
        // Create the array to hold the shapes
        shapes = new FilledOval[MAX_SHAPES];
        
        // Remember that it is currently empty
        numShapes = 0;
    }
    
    /**
     * Add a shape to the collection.  If the collection is already full, this method
     * does nothing.
     * @param newShape the shape to add
     */
    public void addShape (FilledOval newShape) {
        if (numShapes < shapes.length) {
            shapes[numShapes] = newShape;
            numShapes++;
        }
    }
    
    /**
     * Find the topmost shape that contains the point.
     * @param point the coordinate we are looking for.
     * @return the topmost shape at the point.  If there is no shape there, return null.
     */
    public FilledOval getShapeAt (Location point) {
        // We search from the back of the array to the front because the shapes were placed
        // in the order in which they were created.  The topmost shape is at the end of
        // the array.
        for (int i = numShapes - 1; i >= 0; i--) {
            if (shapes[i].contains (point)) {
                return shapes[i];
            }
        }
        
        // No shape there.
        return null;
    }
}