what is the diference between one dimensional for loop and two dimensional for loop

Question

could any one explain me the difference between one dimensional for loop and two dimensional for loop. and how could i change following one dimensional for loop to two dimensional for loop on the second snippet code. thank you

i think following is one dimensional for loop

Capture video;

for(int i = 0; i < video.pixels.length; i++){
    // encoded so blue is > 0 if a pixel is within threshold
    if(blue(video.pixels[i]) > 0){
      count++;
      // processing takes 0-1 (float) color values from shader to 0-255 (int) values for color
      // to decode, we need to divide the color by 255 to get the original value
      avg.add(red(video.pixels[i]) / 255.0, green(video.pixels[i]) / 255.0);
    }
  }

and following snippet code is 2 dimensional for loop

Capture video;
   for (int x = 0; x < video.width && x < 100; x++ ) {
      for (int y = 240; y < video.height; y++ ) {
       int loc = x + y*video.width;
        }
    }

Henhen1227 · Answer 1 · 2022-10-19T01:42:02.973

2

A for loop has 3 parts initialization; condition; increment/decrement Typically used as

for (int x = 0; x < video.width && x < 100; x++ )

Where int x = 0 initializes the variable x. x < video.width && x < 100 checks whether the loop should continue. And x++ increases x every time it finishes one iteration of the loop.

A 2D for is just 2 for loops nested. In the example

for (int x = 0; x < video.width && x < 100; x++ ) {
  for (int y = 240; y < video.height; y++ ) {
   int loc = x + y*video.width;
    }
}

For every increase of x, the for loop will loop through every value 240 ≤ y < video.height.

The 2D for loop is assigning a 1D position to each pixel in the video. You can use this position to read each pixel in video.pixels.

for (int x = 0; x < video.width && x < 100; x++ ) {
   for (int y = 240; y < video.height; y++ ) {
      int loc = x + y*video.width;
      if(blue(video.pixels[loc]) > 0){
         count++;
         avg.add(red(video.pixels[i]) / 255.0, green(video.pixels[i]) / 255.0);
      }
   }
}

Both the code above and your original code achieve the same thing but this way is using a 2D for loop

[Edit 1]

To have the same limits on a 1D for loop is a bit more complicated (untested)

for(int i = 0; i < video.pixels.length; i++){
    const pX = i % video.width;
    const pY = (i - pX) / video.width;
    if(pX > minX && pX < maxX && pY > minY && pY < maxY){
        ... //It is within minX and maxX and within minY and maxY
    }
}

edited Oct 19 '22 at 01:42

answered Oct 18 '22 at 20:49

Henhen1227

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in this code i could limit iteration 'for (int x = 0; x < video.width && x < 100; x++ ) { for (int y = 240; y < video.height; y++ ) { int loc = x + y*video.width; } }' how to do that in with this line 'for(int i = 0; i < video.pixels.length; i++)' – march Oct 18 '22 at 23:37
Why wouldn't you use the 2D for loop? – Henhen1227 Oct 19 '22 at 01:30
I made an edit showing how you could achieve the same limits. However, I think it would be much simpler to use a 2D array. – Henhen1227 Oct 19 '22 at 01:44
for(int i = 0; i < video.pixels.length; i++){ int pX = i % video.width; int pY = (i - pX) / video.width; if(pX > 0 && pX < 100 && pY > 240 && pY < height){ if(blue(posBuffer.pixels[i]) > 0){ count++; // processing takes 0-1 (float) color values from shader to 0-255 (int) values for color // to decode, we need to divide the color by 255 to get the original value avg.add(red(posBuffer.pixels[i]) / 255.0, green(posBuffer.pixels[i]) / 255.0); } } } – march Oct 19 '22 at 03:03
it works to limit the movement of the average circle on x axis but kept drawn the tracked color although the tracked color goes beyond 100 of x axis – march Oct 19 '22 at 03:06

what is the diference between one dimensional for loop and two dimensional for loop

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