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## Rotating an object in a grid

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### #1concepts  Members

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Posted 14 February 2013 - 09:53 PM

Ok, I have been scratching my head for a while, because I couldn't rotate an object. So here's what I would like to know. How do I access shape (an attribute of the class Piece) and how do I change currentPiece (which is an instance of the class object Piece)

Here's what I have done so far for the rotation:

public static int [][] multiplyMatrix(int [][] m1)
{
int [][] m2 =
{{0,0,0,1},
{0,0,1,0},
{0,1,0,0},
{1,0,0,0},
};

int[][] result = new int[4][4];

// multiply
for (int i=0; i<4; i++)
for (int j=0; j<4; j++)
for (int k=0; k<4; k++)
if (m1[i][k] * m2[k][j] > 0)
{
result[i][j] = 1;
}
else
{
result[i][j] = 0;
}

return result;
}


and

    synchronized void rotateClockwise() {
int x = currentX;
int y = currentY;
int [][]s = multiplyMatrix(currentPiece.shape);

currentPiece = new Piece(s, x, y);

updateLocation();
}



it doesn't work, because I can't get access to currentPiece or any of its attribute it seems, even though it was made public.

Here is the full code:

import java.awt.*;

public class Board extends Grid {
public static final int COLUMNS = 16;
public static final int ROWS = 32;
public static final Color BLUE = new Color(0,0,128,40);

public Board() {
super(new int[ROWS][COLUMNS]);
setSize(COLUMNS*Tetris.SQUARE_SIZE,
ROWS*Tetris.SQUARE_SIZE);
}

public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(BLUE);
paintStripes(g);
}

void paintStripes(Graphics g) {
for (int i = 0; i < COLUMNS; i += 4) {
g.fillRect(i*Tetris.SQUARE_SIZE,0,
Tetris.SQUARE_SIZE*2,Tetris.SQUARE_SIZE*ROWS);
}
}

}



Code:

  public class PieceFactory {

public static final int[][] L1 =
{{1,1,0,0},
{0,1,0,0},
{0,1,0,0},
{0,0,0,0},
};

public static final int[][] L2 =
{{0,1,0,0},
{0,1,0,0},
{1,1,0,0},
{0,0,0,0},
};

public static final int[][] T =
{{0,1,0,0},
{1,1,0,0},
{0,1,0,0},
{0,0,0,0},
};

public static final int[][] BOX =
{{1,1,0,0},
{1,1,0,0},
{0,0,0,0},
{0,0,0,0},
};

public static final int[][] BAR =
{{1,1,1,1},
{0,0,0,0},
{0,0,0,0},
{0,0,0,0},
};

public static final int[][] STEP1 =
{{1,0,0,0},
{1,1,0,0},
{0,1,0,0},
{0,0,0,0},
};

public static final int[][] STEP2 =
{{0,1,0,0},
{1,1,0,0},
{1,0,0,0},
{0,0,0,0},
};

public static final int[][][] SHAPES = {L1,L2,T,BOX,BAR,STEP1,STEP2};

public static Piece createPiece() {
int[][] s = SHAPES[(int) (Math.random()*SHAPES.length)];
switch ((int) (Math.random()*10)) {
case 0:
case 1:
case 2:
case 3:
default: return new Piece(s);
}

}

}



Code:

    import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Tetris extends JFrame implements KeyListener {
public static final int SQUARE_SIZE = 10; // 10 by 10 pixels

static Board board;
static Tetris game;

JPanel mainPanel;
public Piece currentPiece;
int score = 0;
JButton scoreButton;

public Tetris() {
super("Tetris");
game = this;
Container pane = getContentPane();
pane.setLayout(new BorderLayout());

scoreButton = new JButton("0");
scoreButton.setEnabled(false);

board = new Board();
mainPanel = new JPanel();
mainPanel.setLayout(null);
mainPanel.setPreferredSize
(new Dimension(Board.COLUMNS*SQUARE_SIZE,
Board.ROWS*SQUARE_SIZE));

public void windowClosing(WindowEvent we) {
System.exit(0);
}
});
pack();
show();
setResizable(false);
}

score += v;
scoreButton.setText(""+score);
}

public int getScore() {
return score;
}

static Board getBoard() {
return board;
}

static Tetris getGame() {
return game;
}

static void sleep(int milliseconds) {
try {
} catch (InterruptedException ie) {
}
}

public static void main(String[] args) {
Tetris game = new Tetris();
while (true) {
game.dropPiece();
}
}

void dropPiece() {
currentPiece = PieceFactory.createPiece();
currentPiece.repaint();
currentPiece.fall();
//mainPanel.remove(currentPiece);
board.repaint();
}

public void keyPressed(KeyEvent event) {
int key = event.getKeyCode();
switch (key) {
case KeyEvent.VK_UP: // up arrow
case KeyEvent.VK_KP_UP:
currentPiece.rotateCounterclockwise();
break;
case KeyEvent.VK_DOWN: // down arrow
case KeyEvent.VK_KP_DOWN:
currentPiece.rotateClockwise();
break;
case KeyEvent.VK_LEFT: // left arrow
case KeyEvent.VK_KP_LEFT:
currentPiece.moveLeft();
break;
case KeyEvent.VK_RIGHT: // right arrow
case KeyEvent.VK_KP_RIGHT:
currentPiece.moveRight();
break;
case KeyEvent.VK_SPACE: // space bar
currentPiece.drop();
}
}

public void keyReleased(KeyEvent arg0) {
}

public void keyTyped(KeyEvent arg0) {
}

}

Code:
public class Piece extends Grid {
int currentX; // current X location on the board
double currentY; // current Y location on the board

public Piece(int shape[][]) {
super(shape);
currentX = 7;
currentY = 2;
updateLocation();
}

public Piece(int shape[][], currentX, currentY) {
super(shape);
this.currentX = currentX;
this.currentY = currentY;
updateLocation()
}

setSize(Tetris.SQUARE_SIZE*getColumns(),
Tetris.SQUARE_SIZE*getRows());
}

void updateLocation() {
setLocation(Tetris.SQUARE_SIZE*currentX,
(int) (Tetris.SQUARE_SIZE*currentY));
}

synchronized void moveDown() {

}

synchronized void moveLeft() {
currentX--;
updateLocation();
}

synchronized void moveRight() {
currentX++;
updateLocation();
}

synchronized void rotateClockwise() {
int x = currentX;
int y = currentY;

currentPiece = new Piece(s, x, y);

updateLocation();
}

synchronized void rotateCounterclockwise() {
}

void fall() {
// replace the following by your code
Tetris.sleep(2000);
}

synchronized void drop() {
currentY++;
updateLocation();
}

public static int [][] multiplyMatrix(int [][] m1)
{
int [][] m2 =
{{0,0,0,1},
{0,0,1,0},
{0,1,0,0},
{1,0,0,0},
};

int[][] result = new int[4][4];

// multiply
for (int i=0; i<4; i++)
for (int j=0; j<4; j++)
for (int k=0; k<4; k++)
if (m1[i][k] * m2[k][j] > 0)
{
result[i][j] = 1;
}
else
{
result[i][j] = 0;
}

return result;
}

}



I can post the files if you really insist. Thanks for helping.

Edited by concepts, 14 February 2013 - 09:58 PM.

### #2Ralara  Members

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Posted 18 February 2013 - 06:42 AM

I'm not 100% on Java so I may be wrong here, hopefully someone can correct me if I am, but although 'currentPiece' is public it is still inside the 'Tetris' class so the 'Piece' class cannot access it directly as you have, but it can access it through a 'Tetris' object. So it would be something like "Tetris.currentPiece", similar to the 'fall()' method where "Tetris.sleep(2000)" is used.

On a side note, there is a way of determining the rotation of Tetris pieces without having to store that location as you have in matrices (some people would argue that using tables is better as there is a limited number of shapes, but I prefer the algorithm personally).

• You define a block in the shape that will be the centre block that will be used to rotate around.
• Each other block is then defined in "shape space" relative to the centre, i.e. a block one column to the left will be [-1,0] relative to the centre block.
• When rotating (CW) the new row is the negative of the current column and the new column is the current row. So from the example above would become [0,1]. (This is still in "shape space", so is an offset from the centre block).
• For CCW rotation the negative is for the new column instead of the new row.

Below is a posting of my code performing the above (note this is in C++ not java);

Vector2 Shape::BlockLocAfterRotate(UINT inBlockNum)
{
// Get the current location of the block
Vector2 outLoc = mBlocks[inBlockNum]->mLoc;

// Location of the centre block for this shape
Vector2 centreLoc = mBlocks[mID_CentreBlock]->mLoc;

// The offset of the current block from the centre of the shape
int offsetRow = centreLoc.y - outLoc.y;
int offsetCol = centreLoc.x - outLoc.x;

// The new location (in shape space)...
int newOffsetRow = -offsetCol; // New row is the negative of the previous col (still in shape space)
int newOffsetCol = offsetRow;  // New col is the previous row (still in shape space)

// Convert back to grid space
outLoc.x = centreLoc.x + newOffsetCol;
outLoc.y = centreLoc.y + newOffsetRow;

return outLoc;
}



Edit: Doing the algorithm way means you can just update the x,y components of your piece instead of having to create a new Piece every time and could very solve your problem too!

### #3BCullis  Members

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Posted 20 February 2013 - 08:35 AM

synchronized void rotateClockwise()

{ int x = currentX;

int y = currentY;

int [][]s = multiplyMatrix(currentPiece.shape);

currentPiece = new Piece(s, x, y);

updateLocation(); }

currentPiece is the variable name you give the piece in the Tetris class.  However, since this method is a member of the Piece class, just replace "currentPiece" with "this".  That will make the method operate on its own instance, which is what you want it to do (and how you're using the method call in the Tetris class, anyway).

Quick edit: been a while since I broke Java, but I'm actually unsure if using "this = new Piece()" will be legit.  You might want to move this functionality into the Tetris class instead, or rethink your method of rotation.  Or I could be fretting over nothing and Java will handle this just fine.  I'm rusty there.

Either way, you can definitely use the "this" keyword in the multiplyMatrix call.

Edited by BCullis, 20 February 2013 - 08:38 AM.

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