/* A simple program where the user can sketch curves and shapes in a variety ofcolors on a variety of background colors. The user selects a drawing color form a pop-up menu at the top of the applet. If the user clicks "Set Background", the background color is set to the current drawing color and the drawing area is filled with that color. If the user clicks "Clear", the drawing area is just filled with the current background color. The user selects the shape to draw from another pop-up menu at the top of the applet. The user can draw free-hand curves, straight lines, and one of six different types of shapes. The user's drawing is saved in an off-screen canvas, which is used to refresh the screen when repainting. The picture is lost if the applet changes size, however. This file defines two classes, SimplePaint3 itself, and a non-public class, SimplePaintCanvas3, that is used by SimplePaint3. */ import java.awt.*; import java.awt.event.*; import java.applet.*; public class SimplePaint3 extends Applet { // The main applet class simply sets up the applet. Most of the // work is done in the canvas. The canvas listens for events from // the buttons. public void init() { setBackground(Color.gray); // Background color of applet, shows // in borders and between components. setLayout(new BorderLayout(3,3)); // Layout manager for applet. SimplePaintCanvas3 canvas = new SimplePaintCanvas3(); // The drawing area. add(canvas,BorderLayout.CENTER); Panel buttonBar = new Panel(); // A panel to hold the buttons. buttonBar.setBackground(Color.lightGray); add(buttonBar, BorderLayout.SOUTH); Panel choiceBar = new Panel(); // A panel to hole the pop-up menus choiceBar.setBackground(Color.lightGray); add(choiceBar, BorderLayout.NORTH); Button fill = new Button("Set Background"); // The first button. fill.addActionListener(canvas); fill.setBackground(Color.lightGray); buttonBar.add(fill); Button clear = new Button("Clear"); // The second button. clear.addActionListener(canvas); clear.setBackground(Color.lightGray); buttonBar.add(clear); Choice choice = new Choice(); // The pop-up menu of colors. choice.addItem("Black"); choice.addItem("Red"); choice.addItem("Green"); choice.addItem("Blue"); choice.addItem("Cyan"); choice.addItem("Magenta"); choice.addItem("Yellow"); choice.addItem("White"); choice.setBackground(Color.white); choiceBar.add(choice); Choice choice2 = new Choice(); // The pop-up menu of shapes. choice2.addItem("Curve"); choice2.addItem("Straight Line"); choice2.addItem("Rectangle"); choice2.addItem("Oval"); choice2.addItem("RoundRect"); choice2.addItem("Filled Rectangle"); choice2.addItem("Filled Oval"); choice2.addItem("Filled RoundRect"); choice2.setBackground(Color.white); choiceBar.add(choice2); canvas.colorChoice = choice; // Canvas needs access to the pop-up menus, canvas.figureChoice = choice2; // so it can check it to find out what // color and shape to use. } // end init() public Insets getInsets() { // Specify how wide a border to leave around the edges of the applet. return new Insets(3,3,3,3); } } // end class SimplePaint3 class SimplePaintCanvas3 extends Canvas implements MouseListener, MouseMotionListener, ActionListener { // A SimplePaintCanvas lets the user use the mouse to draw colored curves // and shapes. The current color is specified by a pop-up menu which // must be created by the applet and assigned to the instance variable // colorChoice. The current shape is specified by another pop-up menu, // figureChoice. The applet listens for action events from buttons // named "Clear" and "Set Background". The "Clear" button fills // the canvas with the current background color. The "Set Background" // sets the background color to the current drawing color and // then clears. private final static int BLACK = 0, RED = 1, // Some constants to make GREEN = 2, // the code more readable. BLUE = 3, // These numbers code for CYAN = 4, // the differnet drawing colors. MAGENTA = 5, YELLOW = 6, WHITE = 7; Choice colorChoice; // A Choice object, containing the possible drawing // colors, which must be created by the applet. private final static int CURVE = 0, LINE = 1, RECT = 2, // Some constants that code OVAL = 3, // for the different types of ROUNDRECT = 4, // figure the program can draw. FILLED_RECT = 5, FILLED_OVAL = 6, FILLED_ROUNDRECT = 7; Choice figureChoice; // A Choice object containg the possible figures. /* Some variables used for double-buffering. */ Image OSC; // The off-screen canvas (created in setupOSC()). int widthOfOSC, heightOfOSC; // Current widht and height of OSC. These // are checked against the size of the applet, // to detect any change in the applet's size. // If the size has changed, a new OSC is created. // The picture in the off-screen canvas is lost // when that happens. /* The following variables are used when the user is sketching a curve while dragging a mouse. */ private int prevX, prevY; // The previous location of the mouse. private int startX, startY; // The starting position of the mouse. // (Not used for drawing curves.) private boolean dragging; // This is set to true when the user is drawing. private int figure; // What type of figure is being drawn. This is // specified by the figureChoice menu. private Graphics graphicsForDrawing; // A graphics context for the applet. private Graphics offscreenGraphics; // A graphics context for the off-screen canvas. SimplePaintCanvas3() { // Constructor. When the canvas is first created, it is set to // listen for mouse events and mouse motion events from // itself. The initial background color is white. addMouseListener(this); addMouseMotionListener(this); setBackground(Color.white); } private void setupOSC() { // This method is responsible for creating the off-screen canvas. // It should be called before using the OSC. It will make a new OSC if // the size of the applet changes. if (OSC == null || widthOfOSC != getSize().width || heightOfOSC != getSize().height) { // Create the OSC, or make a new one if applet size has changed. OSC = null; // (If OSC already exists, this frees up the memory.) OSC = createImage(getSize().width, getSize().height); widthOfOSC = getSize().width; heightOfOSC = getSize().height; Graphics OSG = OSC.getGraphics(); // Graphics context for drawing to OSC. OSG.setColor(getBackground()); OSG.fillRect(0, 0, widthOfOSC, heightOfOSC); } } private Graphics getOSG() { // Return a graphics context for drawing to the off-screen canvas. // A new canvas is created if necessary. Note that the graphics // context should not be kept for any length of time, in case the // size of the canvas changes. setupOSC(); return OSC.getGraphics(); } private void clearOSC() { // Fill the off-screen canvas with the background color. Graphics OSG = OSC.getGraphics(); OSG.setColor(getBackground()); OSG.fillRect(0, 0, widthOfOSC, heightOfOSC); OSG.dispose(); } public void update(Graphics g) { // Redefine update so it doesn't clear the canvas before calling paint(). paint(g); } public void paint(Graphics g) { // Just copy the off-screen canvas to the screen. setupOSC(); g.drawImage(OSC, 0, 0, this); } public void actionPerformed(ActionEvent evt) { // Respond when the user clicks on a button. String command = evt.getActionCommand(); if (command.equals("Clear")) { // Clear the off-screen canvas to current background color, // then call repaint() so the screen is also cleared. clearOSC(); repaint(); } else if (command.equals("Set Background")) { // Set background color, then clear. setBackground(getCurrentColor()); clearOSC(); repaint(); } } private Color getCurrentColor() { // Check the colorChoice menu to find the currently // selected color, and return the appropriate color // object. int currentColor = colorChoice.getSelectedIndex(); switch (currentColor) { case BLACK: return Color.black; case RED: return Color.red; case GREEN: return Color.green; case BLUE: return Color.blue; case CYAN: return Color.cyan; case MAGENTA: return Color.magenta; case YELLOW: return Color.yellow; default: return Color.white; } } private void putFigure(Graphics g, int kind, int x1, int y1, int x2, int y2, boolean outlineOnly) { // Draws a figure with corners at (x1,y1) and (x2,y2). The // parameter "kind" codes for the type of figure to draw. If the // figure is LINE, a line is drawn between the points. For the // other shapes, we need the top-left corner, the width, and the // height of the shape. We have to figure out whether x1 or x2 // is the left edge of the shape and compute the width accordingly. // Similarly for y1 and y2. If outlineOnly is true, then filled shapes // are drawn in outline only. if (kind == LINE) g.drawLine(x1, y1, x2, y2); else { int x, y, w, h; // Top-left corner, width, and height. if (x2 >= x1) { // x1 is left edge x = x1; w = x2 - x1; } else { // x2 is left edge x = x2; w = x1 - x2; } if (y2 >= y1) { // y1 is top edge y = y1; h = y2 - y1; } else { // y2 is top edge. y = y2; h = y1 - y2; } switch (kind) { // Draw the appropriate figure. case RECT: g.drawRect(x, y, w, h); break; case OVAL: g.drawOval(x, y, w, h); break; case ROUNDRECT: g.drawRoundRect(x, y, w, h, 20, 20); break; case FILLED_RECT: if (outlineOnly) g.drawRect(x, y, w, h); else g.fillRect(x, y, w, h); break; case FILLED_OVAL: if (outlineOnly) g.drawOval(x, y, w, h); else g.fillOval(x, y, w, h); break; case FILLED_ROUNDRECT: if (outlineOnly) g.drawRoundRect(x, y, w, h, 20, 20); else g.fillRoundRect(x, y, w, h, 20, 20); break; } } } public void mousePressed(MouseEvent evt) { // This is called when the user presses the mouse on the // canvas. This begins a draw operation in which the user // sketches a curve or draws a shape. if (dragging == true) // Ignore mouse presses that occur return; // when user is already drawing a curve. // (This can happen if the user presses // two mouse buttons at the same time.) prevX = startX = evt.getX(); // Save mouse coordinates. prevY = startY = evt.getY(); figure = figureChoice.getSelectedIndex(); //Type of figure beging drawn. graphicsForDrawing = getGraphics(); // For drawing on the screen. graphicsForDrawing.setColor(getCurrentColor()); offscreenGraphics = getOSG(); // For drawing on the canvas. offscreenGraphics.setColor(getCurrentColor()); if (figure != CURVE) { // Shapes are drawn in XOR mode so they can be erased by redrawing. // Curves are drawn directly to both the screen and to the OSC. graphicsForDrawing.setXORMode(getBackground()); putFigure(graphicsForDrawing, figure, startX, startY, startX, startY, true); } dragging = true; // Start drawing. } // end mousePressed() public void mouseReleased(MouseEvent evt) { // Called whenever the user releases the mouse button. // If the use was drawing a shape, we make the shape // permanent by drawing it in paintMode on both the screen // and the off-screen canvas (but only if the mouse is not // at its starting location.) Then get rid of the graphics // contexts that we were using while dragging. if (dragging == false) return; // Nothing to do because the user isn't drawing. dragging = false; if (figure != CURVE) { // Erase the last XOR mode shape by redrawing it in XOR mode. // Then, if the mouse is not back where it started from, // Draw the final shape on both the screen and the off-screen // canvas in paintMode. putFigure(graphicsForDrawing, figure, startX, startY, prevX, prevY, true); if (startX != prevX || startY != prevY) { graphicsForDrawing.setPaintMode(); putFigure(graphicsForDrawing, figure, startX, startY, prevX, prevY, false); putFigure(offscreenGraphics, figure, startX, startY, prevX, prevY, false); } } graphicsForDrawing.dispose(); offscreenGraphics.dispose(); graphicsForDrawing = null; offscreenGraphics = null; } public void mouseDragged(MouseEvent evt) { // Called whenever the user moves the mouse while a mouse button // is down. If the user is drawing a curve, draw a segment of // the curve on both the screen and the off-screen canvas. // If the user is drawing a shape, erase the previous shape // by redrawing it (in XOR mode), then draw the new shape. if (dragging == false) return; // Nothing to do because the user isn't drawing. int x = evt.getX(); // x-coordinate of mouse. int y = evt.getY(); // y=coordinate of mouse. if (figure == CURVE) { // Draw the line on the applet and on the off-screen canvas. putFigure(graphicsForDrawing, LINE, prevX, prevY, x, y, false); putFigure(offscreenGraphics, LINE, prevX, prevY, x, y, false); } else { // Erase previous figure and draw a new one using the new mouse position. putFigure(graphicsForDrawing, figure, startX, startY, prevX, prevY, true); putFigure(graphicsForDrawing, figure, startX, startY, x, y, true); } prevX = x; // Save coords for the next call to mouseDragged or mouseReleased. prevY = y; } // end mouseDragged. public void mouseEntered(MouseEvent evt) { } // Some empty routines. public void mouseExited(MouseEvent evt) { } // (Required by the MouseListener public void mouseClicked(MouseEvent evt) { } // and MouseMotionListener public void mouseMoved(MouseEvent evt) { } // interfaces). } // end class SimplePaintCanvas3