final static byte GRID = 8;
final static color[][] leds = new color[GRID][GRID];

1. for(int i=0; i<64, i++){
2.       // set the fill color based on if it's the rectangle we're interested in
3.       if( i==indexOfInterest ) fill(255,0,0);
4.       else fill(0);
5.       
6.       draw the rectangle at the prescribed position
7.       rect(rectX[i],rectY[i],rectWidth,rectHeight);
8. }

2. /**
3.  * GridGUI Sample
4.  * by GoToLoop (2013/May)
5.  * edited by Sovereignty314
6.  * http://forum.processing.org/topic/basic-gui
7.  *
8.  * http://studio.processingtogether.com/sp/pad/export/ro.98-pSvW97Q-RE/latest
9.  */
10. 
    
11. final static byte GRID = 8;
12. final static boolean[][] leds = new boolean[GRID][GRID];
13. PrintWriter output;
14. PFont f;
15. final static color ON  = #FF0000, OFF = 0350, BG = 0;
16. final static short DIM = 050;
17. 
    
18. void setup() {
19.   size(GRID*DIM + 100, GRID*DIM + 1, P2D);
20.  // noLoop();
21.   //initGrid();
22.   output = createWriter("matrix.txt");
23.   f=createFont("Serif",20);
24.   textFont(f);
25. }
26. 
    
27. void draw() {
28.   //background(BG);
29.   fill(100);
30.   rect(GRID*DIM+DIM/4,GRID*DIM/2,DIM*2,DIM);
31.   //rect(GRID*DIM+DIM/2,GRID*DIM/4,DIM,DIM);
32.   for (int row = 0; row != GRID; ++row)
33.     for (int col = 0; col != GRID; ++col) {
34.       fill(leds[row][col] ? ON : OFF);
35.       rect(col*DIM, row*DIM, DIM, DIM);
36.     }
37.     //textAlign(RIGHT);
38.   //drawType(GRID*DIM+2.3*DIM);
39.   fill(0);
40.   text("Save frame",GRID*DIM+GRID/2, GRID*DIM-4*DIM-DIM/4);
41. //if(mouseX>(GRID*DIM+DIM/2) && mouseX<(GRID*DIM+DIM/2+DIM) && mouseY>(GRID*DIM/2) && mouseY<(GRID*DIM/2+DIM)&&mousePressed)
42. // fill(255);
43. }
44. 
    
45. void mousePressed() {
46.   redraw();
47.   //initGrid();
48.   for (int row = 0; row != GRID; ++row)
49.     for (int col = 0; col != GRID; ++col) {
50.       if(mouseX>(col*DIM) && mouseX<(col*DIM +DIM) && mouseY>(row*DIM) && mouseY<(row*DIM +DIM))
51.       leds[row][col]= !leds[row][col];
52. }
53. if(mouseX>(GRID*DIM+DIM/2) && mouseX<(GRID*DIM+DIM/2+DIM) && mouseY>(GRID*DIM/2) && mouseY<(GRID*DIM/2+DIM)){
54. saver();
55. output.flush();
56. }
57. //if(mouseX>(GRID*DIM+DIM/2) && mouseX<(GRID*DIM+DIM/2+DIM) && mouseY>(GRID*DIM/4) && mouseY<(GRID*DIM/4+DIM)){
58.  // output.flush();
59. //}
60. 
    
61. //void keyPressed() {
62.  // mousePressed();
63. //}
64. 
    
65. /*void initGrid() {
66.   for (int row = 0; row != GRID; ++row)
67.     for (int col = 0; col != GRID; ++col)
68.       leds[row][col] = random(1) > .5 ? true : false;*/
69. }
70. /*boolean overSave(int x,int y, int w, int h){
71.   if(mouseX >= x && mouseX <= x+w &&  mouseY >= y && mouseY <= y+h)
72.   return true;
73.   else
74.   return false;
75. }*/
76. 
    
77. void saver(){
78.   for (int row = 0; row != GRID; ++row){
79.     output.print("mat.setColumn(0,"+row+",B");
80.     for (int col = 0; col != GRID; ++col) {
81.       if(leds[row][col]==true)
82.       output.print(1);
83.       else
84.       output.print(0);
85.     }
86.     output.print(");");
87.     output.println("");
88.   }
89.   output.print("delay(time);");
90.   output.println("");
91. } 
92. /*void drawType(float x) {
93.   fill(255);
94.   text("Save frame", x, GRID*DIM/1.4);
95. }*/