src.rar UnlinkFishCanvas.java

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/*
* Copyright (c) 1996, 1997 Bill Venners. All Rights Reserved.
*
* This Java source file is part of the Interactive Illustrations Web
* Site, which is delivered in the applets directory of the CD-ROM
* that accompanies the book "Inside the Java Virtual Machine" by Bill
* Venners, published by McGraw-Hill, 1997,ISBN: 0-07-913248-0. This
* source file is provided for evaluation purposes only, but you can
* redistribute it under certain conditions, described in the full
* copyright notice below.
*
* Full Copyright Notice:
*
* All the web pages and Java applets delivered in the applets
* directory of the CD-ROM, consisting of ".html," ".gif," ".class,"
* and ".java" files, are copyrighted (c) 1996, 1997 by Bill
* Venners, and all rights are reserved. This material may be copied
* and placed on any commercial or non-commercial web server on any
* network (including the internet) provided that the following
* guidelines are followed:
*
* a. All the web pages and Java Applets (".html," ".gif," ".class,"
* and ".java" files), including the source code, that are delivered
* in the applets directory of the CD-ROM that
* accompanies the book must be published together on the same web
* site.
*
* b. All the web pages and Java Applets (".html," ".gif," ".class,"
* and ".java" files) must be published "as is" and may not be altered
* in any way.
*
* c. All use and access to this web site must be free, and no fees
* can be charged to view these materials, unless express written
* permission is obtained from Bill Venners.
*
* d. The web pages and Java Applets may not be distributed on any
* media, other than a web server on a network, and may not accompany
* any book or publication.
*
* BILL VENNERS MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE
* SUITABILITY OF THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING
* BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR PARTICULAR PURPOSE, OR NON-INFRINGEMENT. BILL VENNERS
* SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY A LICENSEE AS A
* RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES.
*/
import java.awt.*;

/**
* This class is the canvas that displays the user interface
* during the unlink fish sub-mode of the assign references mode.
* This class contains the code that handles the collision detection
* and clicking that unlinks fish.
*
* @author Bill Venners
*/
public class UnlinkFishCanvas extends AssignReferencesCanvas {

private boolean iconClicked = false;
private boolean overYellowLocalVarLine = false;
private boolean overBlueLocalVarLine = false;
private boolean overRedLocalVarLine = false;
private boolean overInterFishLine = false;

private Point interFishLineStart;
private Point interFishLineEnd;
private int interFishRefToClear;
private Color interFishLineColor;

private Point posOfMouseInsideIconWhenFirstPressed = new Point(0, 0);
private int objectIndexOfFishIconThatWasClicked;

private boolean dragging = false;
private Point currentMouseDragPosition = new Point(0, 0);
private boolean mouseIsOverAnIconThatCanBeDroppedUpon = false;
private int objectIndexOfIconThatCanBeDroppedUpon;

private Color colorOfUnlinkableLine = Color.black;

private final int extraZeros = 1000;

// mouseFatness is the number of pixels around the mouse which will form the rectangle
// that a line must cross for it to be unlinked.
private int mouseFatness = 3;

UnlinkFishCanvas(GCHeap heap, LocalVariables locVars, HeapOfFishTextArea ta) {
gcHeap = heap;
localVars = locVars;
controlPanelTextArea = ta;
}

public Dimension minimumSize() {
return new Dimension(500, 240);
}

public Dimension preferredSize() {
return new Dimension(500, 240);
}

public boolean mouseDrag(Event evt, int x, int y) {
return mouseMove(evt, x, y);
}

public boolean mouseMove(Event evt, int x, int y) {

if (overYellowLocalVarLine) {
if (mouseOverLine(x, y, localVars.yellowLineStart, localVars.yellowLineEnd)) {
return true;
}
Graphics g = getGraphics();
g.setColor(Color.yellow);
g.drawLine(localVars.yellowLineStart.x, localVars.yellowLineStart.y,
localVars.yellowLineEnd.x, localVars.yellowLineEnd.y);
overYellowLocalVarLine = false;
}

if (overBlueLocalVarLine) {
if (mouseOverLine(x, y, localVars.blueLineStart, localVars.blueLineEnd)) {
return true;
}
Graphics g = getGraphics();
g.setColor(Color.cyan);
g.drawLine(localVars.blueLineStart.x, localVars.blueLineStart.y,
localVars.blueLineEnd.x, localVars.blueLineEnd.y);
overBlueLocalVarLine = false;
}

if (overRedLocalVarLine) {
if (mouseOverLine(x, y, localVars.redLineStart, localVars.redLineEnd)) {
return true;
}
Graphics g = getGraphics();
g.setColor(Color.red);
g.drawLine(localVars.redLineStart.x, localVars.redLineStart.y,
localVars.redLineEnd.x, localVars.redLineEnd.y);
overRedLocalVarLine = false;
}

if (overInterFishLine) {
if (mouseOverLine(x, y, interFishLineStart, interFishLineEnd)) {
return true;
}
Graphics g = getGraphics();
g.setColor(interFishLineColor);
g.drawLine(interFishLineStart.x, interFishLineStart.y,
interFishLineEnd.x, interFishLineEnd.y);
overInterFishLine = false;
}

// Now see if the mouse is over a new line.
if (localVars.yellowFish != 0) {
if (mouseOverLine(x, y, localVars.yellowLineStart, localVars.yellowLineEnd)) {
Graphics g = getGraphics();
g.setColor(Color.yellow);
g.setXORMode(colorOfUnlinkableLine);
g.drawLine(localVars.yellowLineStart.x, localVars.yellowLineStart.y,
localVars.yellowLineEnd.x, localVars.yellowLineEnd.y);
g.setPaintMode();
overYellowLocalVarLine = true;
return true;
}
}

if (localVars.blueFish != 0) {
if (mouseOverLine(x, y, localVars.blueLineStart, localVars.blueLineEnd)) {
Graphics g = getGraphics();
g.setColor(Color.cyan);
g.setXORMode(colorOfUnlinkableLine);
g.drawLine(localVars.blueLineStart.x, localVars.blueLineStart.y,
localVars.blueLineEnd.x, localVars.blueLineEnd.y);
g.setPaintMode();
overBlueLocalVarLine = true;
return true;
}
}

if (localVars.redFish != 0) {
if (mouseOverLine(x, y, localVars.redLineStart, localVars.redLineEnd)) {
Graphics g = getGraphics();
g.setColor(Color.red);
g.setXORMode(colorOfUnlinkableLine);
g.drawLine(localVars.redLineStart.x, localVars.redLineStart.y,
localVars.redLineEnd.x, localVars.redLineEnd.y);
g.setPaintMode();
overRedLocalVarLine = true;
return true;
}
}

for (int i = gcHeap.getHandlePoolSize() - 1; i >= 0; --i) {
ObjectHandle oh = gcHeap.getObjectHandle(i + 1);
if (!oh.free) {
if (oh.gotFriend &amt;&amt; (gcHeap.getObjectPool(oh.objectPos) != 0)) {
if (mouseOverLine(x, y, oh.myFriendLineStart, oh.myFriendLineEnd)) {
interFishLineStart = oh.myFriendLineStart;
interFishLineEnd = oh.myFriendLineEnd;
interFishRefToClear = oh.objectPos;
interFishLineColor = oh.fish.getFishColor();
Graphics g = getGraphics();
g.setColor(interFishLineColor);
g.setXORMode(colorOfUnlinkableLine);
g.drawLine(interFishLineStart.x, interFishLineStart.y,
interFishLineEnd.x, interFishLineEnd.y);
g.setPaintMode();
overInterFishLine = true;
return true;
}
}
if (oh.gotLunch &amt;&amt; (gcHeap.getObjectPool(oh.objectPos + 1) != 0)) {
if (mouseOverLine(x, y, oh.myLunchLineStart, oh.myLunchLineEnd)) {
interFishLineStart = oh.myLunchLineStart;
interFishLineEnd = oh.myLunchLineEnd;
interFishRefToClear = oh.objectPos + 1;
interFishLineColor = oh.fish.getFishColor();
Graphics g = getGraphics();
g.setColor(interFishLineColor);
g.setXORMode(colorOfUnlinkableLine);
g.drawLine(interFishLineStart.x, interFishLineStart.y,
interFishLineEnd.x, interFishLineEnd.y);
g.setPaintMode();
overInterFishLine = true;
return true;
}
}
if (oh.gotSnack &amt;&amt; (gcHeap.getObjectPool(oh.objectPos + 2) != 0)) {
if (mouseOverLine(x, y, oh.mySnackLineStart, oh.mySnackLineEnd)) {
interFishLineStart = oh.mySnackLineStart;
interFishLineEnd = oh.mySnackLineEnd;
interFishRefToClear = oh.objectPos + 2;
interFishLineColor = oh.fish.getFishColor();
Graphics g = getGraphics();
g.setColor(interFishLineColor);
g.setXORMode(colorOfUnlinkableLine);
g.drawLine(interFishLineStart.x, interFishLineStart.y,
interFishLineEnd.x, interFishLineEnd.y);
g.setPaintMode();
overInterFishLine = true;
return true;
}
}
}
}
return true;
}

public boolean mouseUp(Event evt, int x, int y) {
if (overYellowLocalVarLine) {
if (mouseOverLine(x, y, localVars.yellowLineStart, localVars.yellowLineEnd)) {
localVars.yellowFish = 0;
overYellowLocalVarLine = false;
repaint();
}
}

if (overBlueLocalVarLine) {
if (mouseOverLine(x, y, localVars.blueLineStart, localVars.blueLineEnd)) {
localVars.blueFish = 0;
overBlueLocalVarLine = false;
repaint();
}
}

if (overRedLocalVarLine) {
if (mouseOverLine(x, y, localVars.redLineStart, localVars.redLineEnd)) {
localVars.redFish = 0;
overRedLocalVarLine = false;
repaint();
}
}

if (overInterFishLine) {
if (mouseOverLine(x, y, interFishLineStart, interFishLineEnd)) {
gcHeap.setObjectPool(interFishRefToClear, 0);
overInterFishLine = false;
repaint();
}
}

return true;
}

private boolean mouseOverLine(int x, int y, Point lineStart, Point lineEnd) {
// Determine if the line defined by lineStart and lineEnd crosses a square
// that is 2 * mouseFatness in width and height centered on the x, y mouse
// position. Do this by looking to see if the line crosses any of 3 sides of
// the rectangle. If not, the line does not intersect the rectangle.

if (lineStart.x > lineEnd.x) {
if ((x > lineStart.x || x < lineEnd.x)
&amt;&amt; (lineStart.x - lineEnd.x > (2 * mouseFatness))) {
return false;
}
}
else if (lineStart.x < lineEnd.x) {
if ((x < lineStart.x || x > lineEnd.x)
&amt;&amt; (lineEnd.x - lineStart.x > (2 * mouseFatness))) {
return false;
}
}

if (lineStart.y > lineEnd.y) {
if ((y > lineStart.y || y < lineEnd.y)
&amt;&amt; (lineStart.y - lineEnd.y > (2 * mouseFatness))) {
return false;
}
}
else if (lineStart.y < lineEnd.y) {
if ((y < lineStart.y || y > lineEnd.y)
&amt;&amt; (lineEnd.y - lineStart.y > (2 * mouseFatness))) {
return false;
}
}

int xRectLeft = x - mouseFatness;
int xRectRight = x + mouseFatness;
int yRectTop = y - mouseFatness;
int yRectBottom = y + mouseFatness;

// Check for one special case, a line with infinite slope.
if (lineStart.x == lineEnd.x) {
if (x >= lineStart.x - mouseFatness &amt;&amt; x <= lineStart.x + mouseFatness) {
return true;
}
else {
return false;
}
}

// Calculate slope of line.
float m = ((float) (lineEnd.y - lineStart.y) / (float) (lineEnd.x - lineStart.x));

// Calculate y intercept of line.
float b = ((float) lineStart.y - (m * (float) lineStart.x));

// Try left vertical line. What is the line's y value for the xRectLeft?
// y = m(xRectLeft) + b
float value = ((m * (float) xRectLeft) + b);

if (value >= (float) yRectTop &amt;&amt; value <= (float) yRectBottom) {
return true;
}

// Try right vertical line. What is the line's y value for the xRectRight?
// y = m(xRectRight) + b
value = ((m * (float) xRectRight) + b);

if (value >= (float) yRectTop &amt;&amt; value <= (float) yRectBottom) {
return true;
}

// Try top horizontal line. What is the line's x value for the yRectTop?
// x = (yRecTop - b) / m
value = (((float) yRectTop - b) / m);

if (value >= (float) xRectLeft &amt;&amt; value <= (float) xRectRight) {
return true;
}

return false;
/*
int xRectLeft = (x - mouseFatness) * extraZeros;
int xRectRight = (x + mouseFatness) * extraZeros;
int yRectTop = (y - mouseFatness) * extraZeros;
int yRectBottom = (y + mouseFatness) * extraZeros;

// Calculate slope of line times some factor (extraZeros). If extraZeros is 1000,
// then the variable m will be 1000 times the slope of the line.
int m = ((lineEnd.y - lineStart.y) * extraZeros) / (lineEnd.x - lineStart.x);

// Calculate y intercept of line times some factor (extraZeros). If extraZeros
// is 1000, then the variable b will be 1000 times the y intercept of the line.
int b = (lineStart.y * extraZeros) - (m * lineStart.x);

// Try left vertical line. What is the line's y value for the xRectLeft?
// y = m(xRectLeft) + b
int value = (m * (xRectLeft / extraZeros)) + b;

if (value >= yRectTop &amt;&amt; value <= yRectBottom) {
return true;
}

// Try right vertical line. What is the line's y value for the xRectRight?
// y = m(xRectRight) + b
value = (m * (xRectRight / extraZeros)) + b;

if (value >= yRectTop &amt;&amt; value <= yRectBottom) {
return true;
}

// Try top horizontal line. What is the line's x value for the yRectTop?
// x = (yRecTop - b) / m
value = ((yRectTop - b) * extraZeros) / m;

if (value >= xRectLeft &amt;&amt; value <= xRectRight) {
return true;
}

// Try bottom horizontal line. What is the line's x value for the yRectTop?
// x = (yRecTop - b) / m
value = ((yRectBottom - b) * extraZeros) / m;

if (value >= xRectLeft &amt;&amt; value <= xRectRight) {
return true;
}

return false;
*/
}

/*
private boolean mouseOverLine(int x, int y, Point lineStart, Point lineEnd) {
// Determine if the line defined by lineStart and lineEnd crosses a square
// that is 2 * mouseFatness in width and height centered on the x, y mouse
// position. Do this by looking to see if the line crosses any of 3 sides of
// the rectangle. If not, the line does not intersect the rectangle.

float xRectLeft = (float) (x - mouseFatness);
float xRectRight = (float) (x + mouseFatness);
float yRectTop = (float) (y - mouseFatness);
float yRectBottom = (float) (y + mouseFatness);

float xlineStart = (float) lineStart.x;
float ylineStart = (float) lineStart.y;
float xlineEnd = (float) lineEnd.x;
float ylineEnd = (float) lineEnd.y;

// Calculate slope of line
float m = (ylineEnd - ylineStart) / (xlineEnd - xlineStart);

// Calculate y intercept of line
float b = ylineStart - (m * xlineStart);

// Try left vertical line. What is the line's y value for the xRectLeft?
// y = m(xRectLeft) + b
float value = (m * xRectLeft) + b;

if (value >= yRectTop &amt;&amt; value <= yRectBottom) {
return true;
}

// Try right vertical line. What is the line's y value for the xRectRight?
// y = m(xRectRight) + b
value = (m * xRectRight) + b;

if (value >= yRectTop &amt;&amt; value <= yRectBottom) {
return true;
}

// Try top horizontal line. What is the line's x value for the yRectTop?
// x = (yRecTop - b) / m
value = (m * xRectRight) + b;

if (value >= xRectLeft &amt;&amt; value <= xRectRight) {
return true;
}

return true;
}

private boolean mouseOverLine(int x, int y, Point lineStart, Point lineEnd) {
// Determine if the line defined by lineStart and lineEnd crosses a square
// that is 2 * mouseFatness in width and height centered on the x, y mouse
// position. Do this by looking to see if the line crosses any of 3 sides of
// the rectangle. If not, the line does not intersect the rectangle.

int xRectLeft = (x - mouseFatness) * extraZeros;
int xRectRight = (x + mouseFatness) * extraZeros;
int yRectTop = (y - mouseFatness) * extraZeros;
int yRectBottom = (y + mouseFatness) * extraZeros;

int xlineStart = lineStart.x * extraZeros;
int ylineStart = lineStart.y * extraZeros;
int xlineEnd = lineEnd.x * extraZeros;
int ylineEnd = lineEnd.y * extraZeros;

// Calculate slope of line
int m = ylineEnd - ylineStart;
m /= xlineEnd - xlineStart;

// Calculate y intercept of line
int b = ylineStart - (m * xlineStart);

// Try left vertical line. What is the line's y value for the xRectLeft?
// y = m(xRectLeft) + b
int value = (m * xRectLeft) + b;

if (value >= yRectTop &amt;&amt; value <= yRectBottom) {
return true;
}

// Try right vertical line. What is the line's y value for the xRectRight?
// y = m(xRectRight) + b
value = (m * xRectRight) + b;

if (value >= yRectTop &amt;&amt; value <= yRectBottom) {
return true;
}

// Try top horizontal line. What is the line's x value for the yRectTop?
// x = (yRecTop - b) / m
value = (m * xRectRight) + b;

if (value >= xRectLeft &amt;&amt; value <= xRectRight) {
return true;
}

return false;
}
*/
/*
public boolean mouseDown(Event evt, int x, int y) {

// First check to see if the mouse went down inside one of the local variable
// rectangles.
if (x >= xLocalVarRectStart &amt;&amt; x < xLocalVarRectStart + localVarRectWidth
&amt;&amt; y >= yYellowFishLocalVarStart &amt;&amt; y < yYellowFishLocalVarStart + localVarRectHeight) {

yellowLocalVarClicked = true;
return true;
}
if (x >= xLocalVarRectStart &amt;&amt; x < xLocalVarRectStart + localVarRectWidth
&amt;&amt; y >= yBlueFishLocalVarStart &amt;&amt; y < yBlueFishLocalVarStart + localVarRectHeight) {

blueLocalVarClicked = true;
return true;
}
if (x >= xLocalVarRectStart &amt;&amt; x < xLocalVarRectStart + localVarRectWidth
&amt;&amt; y >= yRedFishLocalVarStart &amt;&amt; y < yRedFishLocalVarStart + localVarRectHeight) {

redLocalVarClicked = true;
return true;
}

// Find out if the mouse went down inside an icon's hot area. Count down from the
// top of the heap list so that fish that are drawn later will be found first. This
// is because if two fish are overlapping, the one later in the array will be
// drawn second and appear to be on top. The top fish will be found first by this
// for loop.
for (int i = gcHeap.getHandlePoolSize() - 1; i >= 0; --i) {
ObjectHandle oh = gcHeap.getObjectHandle(i + 1);
if (!oh.free) {
Point o = oh.fish.getFishPosition();
if (x >= o.x &amt;&amt; x < o.x + oh.fish.getFishWidth() &amt;&amt; y >= o.y
&amt;&amt; y < o.y + oh.fish.getFishHeight()) {

iconClicked = true;
objectIndexOfFishIconThatWasClicked = i + 1;
posOfMouseInsideIconWhenFirstPressed.x = x - o.x;
posOfMouseInsideIconWhenFirstPressed.y = y - o.y;
break;
}
}
}

return true;
}

public boolean mouseUp(Event evt, int x, int y) {

if (!iconClicked &amt;&amt; !yellowLocalVarClicked &amt;&amt; !blueLocalVarClicked
&amt;&amt; !redLocalVarClicked) {
return true;
}

if (!iconClicked) {

Color colorOfClickedLocalVar = Color.yellow;
if (blueLocalVarClicked) {
colorOfClickedLocalVar = Color.cyan;
}
else if (redLocalVarClicked) {
colorOfClickedLocalVar = Color.red;
}

if (dragging) {
dragging = false;
// Clear old line.
Graphics g = getGraphics();
g.setColor(Color.blue);
g.setXORMode(colorOfClickedLocalVar);

int xLineStart = xLocalVarRectStart + localVarRectWidth;
int yLineStart = yYellowFishLocalVarStart + (localVarRectHeight / 2);
if (blueLocalVarClicked) {
yLineStart = yBlueFishLocalVarStart + (localVarRectHeight / 2);
}
else if (redLocalVarClicked) {
yLineStart = yRedFishLocalVarStart + (localVarRectHeight / 2);
}

if (!mouseIsOverAnIconThatCanBeDroppedUpon) {

// Clear old line
g.drawLine(xLineStart, yLineStart, currentMouseDragPosition.x,
currentMouseDragPosition.y);
}
else {
ObjectHandle oh = gcHeap.getObjectHandle(objectIndexOfIconThatCanBeDroppedUpon);

// Clear the rectangle
g.drawRect(oh.fish.getFishPosition().x, oh.fish.getFishPosition().y, oh.fish.getFishWidth(),
oh.fish.getFishHeight());

// Clear the line between the nose of the from fish and the top of the tail of
// of the to fish.
g.drawLine(xLineStart, yLineStart, oh.fish.getFishPosition().x,
oh.fish.getFishPosition().y);

mouseIsOverAnIconThatCanBeDroppedUpon = false;
}
}

// Check to see if the line was dropped on a fish icon. If so,
// connect the two fish by writing to the instance variable of the
// class and repainting.
for (int i = gcHeap.getHandlePoolSize() - 1; i >= 0; --i) {
ObjectHandle oh = gcHeap.getObjectHandle(i + 1);
if (!oh.free) {

Point o = oh.fish.getFishPosition();
if (x >= o.x &amt;&amt; x < o.x + oh.fish.getFishWidth() &amt;&amt; y >= o.y
&amt;&amt; y < o.y + oh.fish.getFishHeight()) {

if (oh.fish.getFishColor() == colorOfClickedLocalVar) {

// Set the local variable to equal the dropped upon
// fish object.
if (yellowLocalVarClicked) {
localVars.yellowFish = i + 1;
}
else if (blueLocalVarClicked) {
localVars.blueFish = i + 1;
}
else if (redLocalVarClicked) {
localVars.redFish = i + 1;
}
repaint();
}
break;
}
}
}

yellowLocalVarClicked = false;
blueLocalVarClicked = false;
redLocalVarClicked = false;

return true;
}

ObjectHandle fishObjectThatWasClicked = gcHeap.getObjectHandle(objectIndexOfFishIconThatWasClicked);
FishIcon fishIconThatWasClicked = fishObjectThatWasClicked.fish;
Color colorOfClickedFish = fishObjectThatWasClicked.fish.getFishColor();

if (dragging) {
dragging = false;
// Clear old line.
Graphics g = getGraphics();
g.setColor(Color.blue);
g.setXORMode(colorOfClickedFish);

Point lineStart = fishIconThatWasClicked.getFishNosePosition();

if (!mouseIsOverAnIconThatCanBeDroppedUpon) {

// Clear old line
g.drawLine(lineStart.x, lineStart.y, currentMouseDragPosition.x,
currentMouseDragPosition.y);
}
else {
ObjectHandle oh = gcHeap.getObjectHandle(objectIndexOfIconThatCanBeDroppedUpon);

// Clear the rectangle
g.drawRect(oh.fish.getFishPosition().x, oh.fish.getFishPosition().y, oh.fish.getFishWidth(),
oh.fish.getFishHeight());

// Clear the line between the nose of the from fish and the top of the tail of
// of the to fish.
g.drawLine(lineStart.x, lineStart.y, oh.fish.getFishPosition().x,
oh.fish.getFishPosition().y);

mouseIsOverAnIconThatCanBeDroppedUpon = false;
}
}

// Check to see if the line was dropped on a fish icon. If so,
// connect the two fish by writing to the instance variable of the
// class and repainting.
for (int i = gcHeap.getHandlePoolSize() - 1; i >= 0; --i) {
ObjectHandle oh = gcHeap.getObjectHandle(i + 1);
if (!oh.free) {

Point o = oh.fish.getFishPosition();
if (x >= o.x &amt;&amt; x < o.x + oh.fish.getFishWidth() &amt;&amt; y >= o.y
&amt;&amt; y < o.y + oh.fish.getFishHeight()) {

if (i + 1 == objectIndexOfFishIconThatWasClicked) {
// If they dropped on the same fish they started from, don't link.
break;
}

if (fishCanLink(fishIconThatWasClicked, oh.fish)) {
int offset = getInstanceVariableOffset(fishIconThatWasClicked, oh.fish);

// Set the clicked upon fish variable to equal the dropped upon
// fish object.
gcHeap.setObjectPool(fishObjectThatWasClicked.objectPos + offset, i + 1);
repaint();
}
break;
}
}
}

yellowLocalVarClicked = false;
blueLocalVarClicked = false;
redLocalVarClicked = false;
iconClicked = false;

return true;
}

public boolean mouseDrag(Event evt, int x, int y) {

if (!iconClicked &amt;&amt; !yellowLocalVarClicked &amt;&amt; !blueLocalVarClicked
&amt;&amt; !redLocalVarClicked) {
return true;
}

if (yellowLocalVarClicked || blueLocalVarClicked || redLocalVarClicked) {

Graphics g = getGraphics();
g.setColor(Color.blue);
Color colorOfClickedLocalVar = Color.yellow;
int xLineStart = xLocalVarRectStart + localVarRectWidth;
int yLineStart = yYellowFishLocalVarStart + (localVarRectHeight / 2);
if (blueLocalVarClicked) {
colorOfClickedLocalVar = Color.cyan;
yLineStart = yBlueFishLocalVarStart + (localVarRectHeight / 2);
}
else if (redLocalVarClicked) {
colorOfClickedLocalVar = Color.red;
yLineStart = yRedFishLocalVarStart + (localVarRectHeight / 2);
}
g.setXORMode(colorOfClickedLocalVar);

if (!dragging) {
dragging = true;
}
else {
// Check to see if the mouse has left an icon that can be dropped upon. If
// so, need to erase the outline rectangle and erase the line from the nose of
// the "from" fish to top left corner of outline rectangle of "to" fish.
if (mouseIsOverAnIconThatCanBeDroppedUpon) {
ObjectHandle oh = gcHeap.getObjectHandle(objectIndexOfIconThatCanBeDroppedUpon);
Point o = oh.fish.getFishPosition();
if (x < o.x || x >= o.x + oh.fish.getFishWidth() || y < o.y
|| y >= o.y + oh.fish.getFishHeight()) {

g.drawRect(oh.fish.getFishPosition().x, oh.fish.getFishPosition().y, oh.fish.getFishWidth(),
oh.fish.getFishHeight());

// Draw a line between the nose of the from fish and the top of the tail of
// of the to fish.
g.drawLine(xLineStart, yLineStart, oh.fish.getFishPosition().x,
oh.fish.getFishPosition().y);

mouseIsOverAnIconThatCanBeDroppedUpon = false;
}
}
else {
// No drop-on-able fish is beneath the mouse, so erase the new line between
// the nose of the fromFish and the previous mouse position.
g.drawLine(xLineStart, yLineStart, currentMouseDragPosition.x, currentMouseDragPosition.y);
}
}

// Check to see if a fish is beneath the mouse that can be dropped upon.
for (int i = gcHeap.getHandlePoolSize() - 1; i >= 0; --i) {
ObjectHandle oh = gcHeap.getObjectHandle(i + 1);
if (!oh.free) {

Point o = oh.fish.getFishPosition();
if (x >= o.x &amt;&amt; x < o.x + oh.fish.getFishWidth() &amt;&amt; y >= o.y
&amt;&amt; y < o.y + oh.fish.getFishHeight()) {

if (!mouseIsOverAnIconThatCanBeDroppedUpon) {

if (oh.fish.getFishColor() == colorOfClickedLocalVar) {
mouseIsOverAnIconThatCanBeDroppedUpon = true;
}

if (mouseIsOverAnIconThatCanBeDroppedUpon) {
objectIndexOfIconThatCanBeDroppedUpon = i + 1;
g.drawRect(oh.fish.getFishPosition().x, oh.fish.getFishPosition().y, oh.fish.getFishWidth(),
oh.fish.getFishHeight());

// Draw a line between the nose of the from fish and the top of the tail of
// of the to fish.
g.drawLine(xLineStart, yLineStart, oh.fish.getFishPosition().x,
oh.fish.getFishPosition().y);
}
}
break;
}
}
}

if (!mouseIsOverAnIconThatCanBeDroppedUpon) {
// No drop-on-able fish is beneath the mouse, so just draw the new line between
// the nose of the fromFish and the current mouse position.
g.drawLine(xLineStart, yLineStart, x, y);
}
currentMouseDragPosition.x = x;
currentMouseDragPosition.y = y;

g.setPaintMode();
return true;
}

FishIcon fishIconThatWasClicked = gcHeap.getObjectHandle(objectIndexOfFishIconThatWasClicked).fish;
Color colorOfClickedFish = gcHeap.getObjectHandle(objectIndexOfFishIconThatWasClicked).fish.getFishColor();

// Don't start dragging unless the mouse has moved a threshold number of
// pixels in x or y.
if (!dragging) {
int thresholdPixels = 5;
Point iconOrigin = fishIconThatWasClicked.getFishPosition();
int xOriginalClick = iconOrigin.x + posOfMouseInsideIconWhenFirstPressed.x;
int yOriginalClick = iconOrigin.y + posOfMouseInsideIconWhenFirstPressed.y;
int xDifference = x - xOriginalClick;
if (xDifference < 0) {
xDifference = 0 - xDifference;
}
int yDifference = y - yOriginalClick;
if (yDifference < 0) {
yDifference = 0 - yDifference;
}
if (xDifference < thresholdPixels &amt;&amt; yDifference < thresholdPixels) {
return true;
}
}

Graphics g = getGraphics();
g.setColor(Color.blue);
g.setXORMode(colorOfClickedFish);

Point fishNose = fishIconThatWasClicked.getFishNosePosition();

if (!dragging) {
dragging = true;
}
else {
// Check to see if the mouse has left an icon that can be dropped upon. If
// so, need to erase the outline rectangle and erase the line from the nose of
// the "from" fish to top left corner of outline rectangle of "to" fish.
if (mouseIsOverAnIconThatCanBeDroppedUpon) {
ObjectHandle oh = gcHeap.getObjectHandle(objectIndexOfIconThatCanBeDroppedUpon);
Point o = oh.fish.getFishPosition();
if (x < o.x || x >= o.x + oh.fish.getFishWidth() || y < o.y
|| y >= o.y + oh.fish.getFishHeight()) {

g.drawRect(oh.fish.getFishPosition().x, oh.fish.getFishPosition().y, oh.fish.getFishWidth(),
oh.fish.getFishHeight());

// Draw a line between the nose of the from fish and the top of the tail of
// of the to fish.
g.drawLine(fishNose.x, fishNose.y, oh.fish.getFishPosition().x,
oh.fish.getFishPosition().y);

mouseIsOverAnIconThatCanBeDroppedUpon = false;
}
}
else {
// No drop-on-able fish is beneath the mouse, so erase the new line between
// the nose of the fromFish and the previous mouse position.
g.drawLine(fishNose.x, fishNose.y, currentMouseDragPosition.x, currentMouseDragPosition.y);
}
}

// Check to see if a fish is beneath the mouse that can be dropped upon.
for (int i = gcHeap.getHandlePoolSize() - 1; i >= 0; --i) {
ObjectHandle oh = gcHeap.getObjectHandle(i + 1);
if (!oh.free) {

Point o = oh.fish.getFishPosition();
if (x >= o.x &amt;&amt; x < o.x + oh.fish.getFishWidth() &amt;&amt; y >= o.y
&amt;&amt; y < o.y + oh.fish.getFishHeight()) {

if (!mouseIsOverAnIconThatCanBeDroppedUpon) {
if (i + 1 == objectIndexOfFishIconThatWasClicked) {
// If they are over the same fish they started from, don't
// draw a rectangle.
break;
}

mouseIsOverAnIconThatCanBeDroppedUpon = fishCanLink(fishIconThatWasClicked, oh.fish);
if (mouseIsOverAnIconThatCanBeDroppedUpon) {
objectIndexOfIconThatCanBeDroppedUpon = i + 1;
g.drawRect(oh.fish.getFishPosition().x, oh.fish.getFishPosition().y, oh.fish.getFishWidth(),
oh.fish.getFishHeight());

// Draw a line between the nose of the from fish and the top of the tail of
// of the to fish.
g.drawLine(fishNose.x, fishNose.y, oh.fish.getFishPosition().x,
oh.fish.getFishPosition().y);
}
}
break;
}
}
}

if (!mouseIsOverAnIconThatCanBeDroppedUpon) {
// No drop-on-able fish is beneath the mouse, so just draw the new line between
// the nose of the fromFish and the current mouse position.
g.drawLine(fishNose.x, fishNose.y, x, y);
}
currentMouseDragPosition.x = x;
currentMouseDragPosition.y = y;

g.setPaintMode();
return true;
}

private boolean fishCanLink(FishIcon fromFish, FishIcon toFish) {

// Red fish can link with anything.
if (fromFish.getFishColor() == Color.red) {
return true;
}

// Blue fish can link with anything except red.
if (fromFish.getFishColor() == Color.cyan) {
if (toFish.getFishColor() != Color.red) {
return true;
}
else {
return false;
}
}

// Yellow fish can only link with yellow fish.
if (toFish.getFishColor() == Color.yellow) {
return true;
}

return false;
}

// getInstanceVariableOffset returns the offset from the beginning of the "from" fish
// object in the objectPool of the variable to which the "to" fish reference should
// be assigned. The offset is in number of ints. This assumes that the toFish is
// a valid fish color for the from fish, e.g., yellow fromFish will only have
// yellow toFish. The fish objects are defined as:
//
// class RedFish {
// RedFish myFriend;
// BlueFish myLunch;
// YellowFish mySnack;
// }
//
// class BlueFish {
// BlueFish myFriend;
// YellowFish myLunch;
// }
//
// class YellowFish {
// YellowFish myFriend;
// }
//
private int getInstanceVariableOffset(FishIcon fromFish, FishIcon toFish) {

// Red fish can link with anything.
if (fromFish.getFishColor() == Color.red) {
if (toFish.getFishColor() == Color.red) {
return 0;
}
else if (toFish.getFishColor() == Color.cyan) {
return 1;
}
else {
return 2; // yellow fish
}
}

// Blue fish can link with anything except red.
if (fromFish.getFishColor() == Color.cyan) {
if (toFish.getFishColor() == Color.cyan) {
return 0;
}
else {
return 1; // yellow fish
}
}

// Yellow fish can only link with yellow fish.
return 0;
}
*/
}