/* A simple program where the user can sketch curves in a variety of colors. A color palette is shown on the right of the applet. The user can select a drawing color by clicking on a color in the palette. Under the colors is a "Clear button" that the user can press to clear the sketch. The user draws by clicking and dragging in a large white area that occupies most of the applet. The user's drawing is not persistant. It is cleared if the applet is resized. If it is covered, in whole or part, and then uncovered, the part was covered is gone. */ import java.awt.*; import java.awt.event.*; import java.applet.*; public class SimplePaint extends Applet implements MouseListener, MouseMotionListener { 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; private int currentColor = BLACK; // The currently selected drawing color, // coded as one of the above constants. /* 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 boolean dragging; // This is set to true while the user is drawing. private Graphics graphicsForDrawing; // A graphics context for the applet // that is used to draw the user's curve. public void init() { // When the applet is first created, the applet is set to // listen for mouse events and mouse motion events from // itself. addMouseListener(this); addMouseMotionListener(this); } public void update(Graphics g) { // Redefine update so it does not fill the applet with the // background color before calling paint(). This is OK // since the paint() method always draws over the entire // surface of the applet. paint(g); } public void paint(Graphics g) { // Draw the contents of the applet. Since no information is // saved about what the user has drawn, the user's drawing // is erased whenever this routine is called. int width = getSize().width; // Width of the applet. int height = getSize().height; // Height of the applet. int colorSpacing = (height - 56) / 7; // Distance between the top of one colored rectangle in the palette // and the top of the rectangle below it. The height of the // rectangle will be colorSpacing - 3. There are 7 colored rectangles, // so the available space is divided by 7. The available space allows // for the gray border and the 50-by-50 CLEAR button. /* First, fill in the white drawing area, allowing for a three-pixel border at top, bottom, and left and allowing for the 56-pixel wide strip on the right that is occupied by the color palette and CLEAR button. (I could just fill the whole applet with white and then draw over some of it, but that leads to increased flickering when the applet is redrawn.) */ g.setColor(Color.white); g.fillRect(3, 3, width - 59, height - 6); /* Draw a 3-pixel border around the applet in gray. This has to be done by drawing three rectangles of different sizes. */ g.setColor(Color.gray); g.drawRect(0, 0, width-1, height-1); g.drawRect(1, 1, width-3, height-3); g.drawRect(2, 2, width-5, height-5); /* Draw a 56-pixel wide gray rectangle along the right edge of the applet. The color palette and Clear button will be drawn on top of this. (This covers some of the same area as the border I just drew. */ g.fillRect(width - 56, 0, 56, height); /* Draw the "Clear button" as a 50-by-50 white rectangle in the lower right corner of the applet, allowing for a 3-pixel border. */ g.setColor(Color.white); g.fillRect(width-53, height-53, 50, 50); g.setColor(Color.black); g.drawRect(width-53, height-53, 49, 49); g.drawString("CLEAR", width-48, height-23); /* Draw the seven color rectangles. */ g.setColor(Color.black); g.fillRect(width-53, 3 + 0*colorSpacing, 50, colorSpacing-3); g.setColor(Color.red); g.fillRect(width-53, 3 + 1*colorSpacing, 50, colorSpacing-3); g.setColor(Color.green); g.fillRect(width-53, 3 + 2*colorSpacing, 50, colorSpacing-3); g.setColor(Color.blue); g.fillRect(width-53, 3 + 3*colorSpacing, 50, colorSpacing-3); g.setColor(Color.cyan); g.fillRect(width-53, 3 + 4*colorSpacing, 50, colorSpacing-3); g.setColor(Color.magenta); g.fillRect(width-53, 3 + 5*colorSpacing, 50, colorSpacing-3); g.setColor(Color.yellow); g.fillRect(width-53, 3 + 6*colorSpacing, 50, colorSpacing-3); /* Draw a 2-pixel white border around the color rectangle of the current drawing color. */ g.setColor(Color.white); g.drawRect(width-55, 1 + currentColor*colorSpacing, 53, colorSpacing); g.drawRect(width-54, 2 + currentColor*colorSpacing, 51, colorSpacing-2); } // end paint() private void changeColor(int y) { // Change the drawing color after the user has clicked the // mouse on the color palette at a point with y-coordinate y. // (Note that I can't just call repaint and redraw the whole // applet, since that whould erase the user's drawing.) int width = getSize().width; // Width of applet. int height = getSize().height; // Height of applet. int colorSpacing = (height - 56) / 7; // Space for one color rectangle. int newColor = y / colorSpacing; // Which color number was clicked? if (newColor < 0 || newColor > 6) // Make sure the color number is valid. return; /* Remove the hilite from the current color, by drawing over it in gray. Then change the current drawing color and draw a hilite around the new drawing color. */ Graphics g = getGraphics(); g.setColor(Color.gray); g.drawRect(width-55, 1 + currentColor*colorSpacing, 53, colorSpacing); g.drawRect(width-54, 2 + currentColor*colorSpacing, 51, colorSpacing-2); currentColor = newColor; g.setColor(Color.white); g.drawRect(width-55, 1 + currentColor*colorSpacing, 53, colorSpacing); g.drawRect(width-54, 2 + currentColor*colorSpacing, 51, colorSpacing-2); g.dispose(); } // end changeColor() private void setUpDrawingGraphics() { // This routine is called in mousePressed when the // user clicks on the drawing area. It sets up the // graphics context, graphicsForDrawing, to be used // to draw the user's sketch in the current color. graphicsForDrawing = getGraphics(); switch (currentColor) { case BLACK: graphicsForDrawing.setColor(Color.black); break; case RED: graphicsForDrawing.setColor(Color.red); break; case GREEN: graphicsForDrawing.setColor(Color.green); break; case BLUE: graphicsForDrawing.setColor(Color.blue); break; case CYAN: graphicsForDrawing.setColor(Color.cyan); break; case MAGENTA: graphicsForDrawing.setColor(Color.magenta); break; case YELLOW: graphicsForDrawing.setColor(Color.yellow); break; } } // end setUpDrawingGraphics() public void mousePressed(MouseEvent evt) { // This is called when the user presses the mouse anywhere // in the applet. There are three possible responses, // depending on where the user clicked: Change the // current color, clear the drawing, or start drawing // a curve. (Or do nothing if user clicks on the border.) int x = evt.getX(); // x-coordinate where the user clicked. int y = evt.getY(); // y-coordinate where the user clicked. int width = getSize().width; // Width of the applet. int height = getSize().height; // Height of the applet. 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.) if (x > width - 53) { // User clicked to the right of the drawing area. // This click is either on the clear button or // on the color palette. if (y > height - 53) repaint(); // Clicked on "CLEAR button". else changeColor(y); // Clicked on the color palette. } else if (x > 3 && x < width - 56 && y > 3 && y < height - 3) { // The user has clicked on the white drawing area. // Start drawing a curve from the point (x,y). prevX = x; prevY = y; dragging = true; setUpDrawingGraphics(); } } // end mousePressed() public void mouseReleased(MouseEvent evt) { // Called whenever the user releases the mouse button. // If the user was drawing a curve, the curve is done, // so we should set drawing to false and get rid of // the graphics context that we created to use during // the drawing. if (dragging == false) return; // Nothing to do because the user isn't drawing. dragging = false; graphicsForDrawing.dispose(); graphicsForDrawing = null; } public void mouseDragged(MouseEvent evt) { // Called whenever the user moves the mouse // while a mouse button is held down. If the // user is drawing, draw a line segment from the // previous mouse location to the current mouse // location, and set up prevX and prevY for the // next call. Note that in case the user drags // ouside of the drawing area, the values of // x and y are "clamped" to lie within this // area. This avoids drawing on the color palette // or clear buton. 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 (x < 3) // Adjust the value of x, x = 3; // to make sure it's in if (x > getSize().width - 57) // the drawing area. x = getSize().width - 57; if (y < 3) // Adjust the value of y, y = 3; // to make sure it's in if (y > getSize().height - 4) // the drawing area. y = getSize().height - 4; graphicsForDrawing.drawLine(prevX, prevY, x, y); // Draw the line. prevX = x; // Get ready for the next line segment in the curve. 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 SimplePaint