Java: how to rotate a non squared 2D array

Question

I have this as a color array:

public RGBImage(int width, int height, RGBColor background) {
      pixel =  new RGBColor[width][height];
      this.w = width;
      this.h = height;
      this.b = background;

      for(x = 0; x < width; x++){
          for(y = 0; y < height; y++){
              pixel[x][y] = b;
          }
      }

and i want to rotate it, right, the code is already doing good regarding square matrix thanks to @Oblivion Creations, but I'm getting outofbounds errors when using it non squared matrixes

   public void rotateRight() {
      RGBColor[][] mirror = new RGBColor[h][w];
              for(int i = 0 ; i < h; i++){
                  for(int j = 0 ; j < w; j++){
                      mirror[i][j] = pixel[j][w-i-1];
                  }
              }
            pixel = mirror;
  }

Andrew Alderson · Accepted Answer · 2014-10-17 04:00:48Z

2

I think the problem is mirror = pixel; sharing the same reference... So it is altering itself as it is rotating, causing it to do weird and wonderful things.

My suggestion would be to copy from pixel to the mirror, then assign the mirror to pixel after the for loop, like so:

public void rotateLeft() {
    RGBColor[][] mirror = new RGBColor[w][h];
    if(w == h){
        for(int i = 0 ; i < h; i++){
            for(int j = 0 ; j < h; j++){
                mirror[i][j] = pixel[h-j-1][i];
            }
        }
        pixel = mirror;
    }
}

Edit:

For your new RotateRight, you're using the width variable instead of the height on the unrotated pixel array. Try this instead:

public void rotateRight() {
   RGBColor[][] mirror = new RGBColor[h][w];
           for(int i = 0 ; i < h; i++){
               for(int j = 0 ; j < w; j++){
                   mirror[i][j] = pixel[j][h-i-1];
               }
           }
         pixel = mirror;
}

edited Oct 17, 2014 at 4:00

answered Oct 16, 2014 at 23:17

Andrew Alderson

90312 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

bknight Over a year ago

thanks man, it worked like a charm! any tips on upgrading this to a non square matrix?

Andrew Alderson Over a year ago

No worries! Actually yeah, I was thinking about that after I answered... Change the creation of mirror to RGBColor[][] mirror = new RGBColor[h][w]; (reversing the width and height), remove the if check and it should be right to go.

bknight Over a year ago

yeah I've done it that way, now just have to solve something wrong with the loops, currenty doing it this way: pastebin.com/pXKxH73p but having out of bounds, which makes sense, just quite haven't figure it out to stop it on time. thx again.

Andrew Alderson Over a year ago

mirror[i][j] = pixel[j][w-i-1]; should be mirror[i][j] = pixel[j][h-i-1];

bknight Over a year ago

yeah it's rotating fine now! last problem is my getRGB algorithm which is messing up when h != w, pastebin.com/JVHAe55y , cant really find why. thx again for all the help.

Code-Apprentice · Accepted Answer · 2014-10-16 23:21:48Z

0

The problem is that mirror = pixel assigns mirror to refer to the same array as pixel. It does not copy the array. So then in your loop, pixel[i][j] = mirror[h-j-1][i] copies a pixel from one cell of the array to another cell of the same array.

answered Oct 16, 2014 at 23:21

Code-Apprentice

84k26 gold badges162 silver badges289 bronze badges

Collectives™ on Stack Overflow

Java: how to rotate a non squared 2D array

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related