When I draw rectangles in a JPanel, not all of them display. Why do some rectangles in the first column not display?

Question

Right now, I'm working on making a version of Tetris. To test out my Graphics class, I'm first trying to draw 200 gray squares (10x20) before I worry about drawing the piece. I have two 2D arrays called myRectangles (which has coordinates, height, width), and myColors, which stores the color of each square. Right now it's just all Color.DARK_GRAY.

In my constructor, I set up the arrays like this:

for(int i = 0; i < width; i++)
  {
     for(int j = 0; j < height; j++)
     {
        myColors[i][j] = Color.DARK_GRAY;
        myRectangles[i][j] = new Rectangle2D.Double(INITIAL_X + (i * SQUARE_SIDE),
                                           INITIAL_Y + (j * SQUARE_SIDE),
                                           SQUARE_SIDE, SQUARE_SIDE);
     }
  }

Then, I have a separate drawBoard method, because I'll want to be able to call this multiple times when I actually start drawing pieces on the board. That method looks like this (note that I have some test code in the method):

public void drawBoard()
{
  Graphics g = myGame.getGraphics();
  Graphics2D g2 = (Graphics2D) g;

  int counter = 0;
  for(int i = 0; i < TetrisBoard.MAX_WIDTH; i++)
  {
     for(int j = 0; j < TetrisBoard.MAX_HEIGHT; j++)
     {
        g2.setPaint(myColors[i][j]);
        g2.fill(myRectangles[i][j]);
        System.out.println(counter);
        System.out.println("Drawing rectangle at " + myRectangles[i][j].getX() + " " + myRectangles[i][j].getY());
        System.out.println("Color " + myColors[i][j]);
        System.out.println();
        counter++;
     } 
  }
  System.out.println(counter);
  myGame.setVisible(true);
  myWindow.setVisible(true);
 }

Typically, when I run the code, it misses a few squares in the first column. When I use the debugger, it appears correctly.

score 0 · Answer 1 · answered Apr 21 '15 at 04:02

Don't use the getGraphics() method to do painting.

Custom painting is done by overriding the paintComponent() method of a JPanel. Then you add the panel to the frame.

Read the section from the Swing tutorial on Custom Painting for more information and working examples.

When I draw rectangles in a JPanel, not all of them display. Why do some rectangles in the first column not display?

1 Answers1