CSCI A201/A597 Lab Notes 8 Spring 2000

A few pointers:

• You will be using the element package. Make sure you have it on your floppy.

• You will be using a DrawingWindow. Make sure you read about it in your book page 43, chapter 2.

• You will be drawing lines and rectangles on it. Make sure you read about
  1. window coordinate system
  2. drawing lines and
  3. drawing rectangles
  in your book. (pages 43-47 and 50-51)

• You will be getting input from the mouse. Read about it on pp. 47-50.

• You will have to determine if you are inside a rectangle or not. This can be done by checking if each of the two coordinates of the point of interest fall in between the corresponding coordinates of the margins of the rectangle. See page 72 for an example of a program that does that, and another one on page 53.

• You will have to change the color and draw filled rectangles. This is also described on pp. 56-60 (for the colors) and on page 51 drawing filled rectangles.

Develop your program in stages:

1. first make it draw the grid
2. then add the two rectangles for erase and exit
3. then get your window to report mouse clicks (to do that properly you need to accept any number of clicks so an infinite loop would be the most appropriate setting for that)
4. if you report the clicks start paying attention to the x and y of the points where the mouse is clicked
5. then make sure that your program exits when the right square is clicked
6. then redraw the original grid when the other square is clicked
7. then make the program place red filled squares at the point where the mouse was clicked, regardless of the location
8. then restrict this to happen only inside the grid
9. then find the cell in which the mouse was clicked and draw the filled red square on top of that one, precisely

I will update this set of notes later but hopefully this should give you a starting point. Here are some stages in the program development:

1. Creating a drawing window.

import element.*; // page 37

public class dgerman7 {
  public static void main(String[] args) {
    DrawingWindow d = new DrawingWindow(); // page 44

  } 
}

import element.*; 

public class dgerman7 {
  public static void main(String[] args) {
    DrawingWindow d = new DrawingWindow(); // page 44

    d.awaitMousePress(); // pages 47-49 
    System.out.println("The mouse has been pressed."); 

  } 
} 

import element.*; 

public class dgerman7 {
  public static void main(String[] args) {
    DrawingWindow d = new DrawingWindow(); // page 44
    int i = 0; 
    while (true) 
    { d.awaitMousePress(); // pages 47-49 
      i = i + 1; 
      System.out.println("The mouse has been pressed " + i + " times."); 
      // this prints the message continuously while the 
      // mouse button is being kept pressed down 
    }

  } 
} 

import element.*; 

public class dgerman7 {
  public static void main(String[] args) {
    DrawingWindow d = new DrawingWindow(); // page 44
    int i = 0; 
    while (true) 
    { d.awaitMousePress(); // pages 47-49 
      i = i + 1; 
      System.out.println("The mouse has been pressed " + i + " times."); 
      d.awaitMouseRelease(); // page 51
      // makes sure one message is printed per interval
      // of time that the mouse is being kepT pressed
    }

  } 
} 

5. Drawing a rectangle.

import element.*; 

public class dgerman7 {
  public static void main(String[] args) {
    DrawingWindow d = new DrawingWindow(); // page 44

    // Drawing a rectangle: pages 50 and 316 

    Rect r = new Rect(40, // x coord of top left corner 
                      10, // y coord of top left corner 
                      10, // width in pixels (horizontal) 
                      40); // height in pixels 

    // this creates the rectangle but doesn't draw it 
    // to draw it you need to let the windown know that
    // the rectangle should be drawn

    d.draw(r); // page 50 -- ask d to draw r 

    while (true) { 
      d.awaitMousePress();   // pages 47-49 
      d.awaitMouseRelease(); // page 51
    }
  } 
} 

import element.*;

public class dgerman7 {
  public static void main(String[] args) {
    DrawingWindow d = new DrawingWindow(); // page 44

    // Drawing a rectangle: pages 50 and 316 

    Rect r = new Rect(40, // x coord of top left corner 
                      10, // y coord of top left corner 
                      10, // width in pixels (horizontal) 
                      40); // height in pixels 

    // this creates the rectangle but doesn't draw it 
    // to draw it you need to let the windown know that
    // the rectangle should be drawn

    d.draw(r); // page 50 -- ask d to draw r 

    Pt press; // define this like in the example on pages 52-53 
    // Points are described on page 45-47 and appendix E p. 312

    while (true) { 
      press = d.awaitMousePress();   // pages 47-49, 52-53 

      System.out.println("Mouse pressed at (" +  // text 
                          press.x() // invoke x() on press to get x coordinate
                          + ", " +  // text 
                          press.y() // obtain the y coordinate of the point  
                          + ")"     // text 
                        );  
      d.awaitMouseRelease(); // page 51
    }
  } 
} 

The only addition to the program from step 6 is marked in blue

import element.*; 

public class dgerman7 {
  public static void main(String[] args) {
    DrawingWindow d = new DrawingWindow(); // page 44

    // Drawing a rectangle: pages 50 and 316 

    Rect r = new Rect(40, // x coord of top left corner 
                      10, // y coord of top left corner 
                      10, // width in pixels (horizontal) 
                      40); // height in pixels 

    // this creates the rectangle but doesn't draw it 
    // to draw it you need to let the windown know that
    // the rectangle should be drawn

    d.draw(r); // page 50 -- ask d to draw r 

    Pt press; // define this like in the example on pages 52-53 
    // Points are described on page 45-47 and appendix E p. 312

    while (true) { 
      press = d.awaitMousePress();   // pages 47-49, 52-53 

      System.out.println("Mouse pressed at (" +  // text 
                          press.x() // invoke x() on press to get x coordinate
                          + ", " +  // text 
                          press.y() // obtain the y coordinate of the point  
                          + ")"     // text 
                        );  


      if (press.x() > 40 && press.x() < 40 + 10 && 
          press.y() > 10 && press.y() < 10 + 40 ) {
        System.out.println("Mouse clicked inside rectangle, program closing.");
        System.exit(0); 
      }  

      d.awaitMouseRelease(); // page 51
    }
  } 
}