How do I nest this for loop?

gurung Published at Dev

gurung

I am trying to create an image with a pattern of a repeated circle. I am doing this in PHP with GD. So far I have been able to tile the circle in horizontal manner (x-axis) but am unable to tile it in the vertical(y-axis). Here is an example image.

Below is the code that created the above image :

$width = 1000; 
$height = 500;

$image_p = imagecreatetruecolor($width, $height); 
$color = imagecolorallocate($image_p, 0, 255, 0); 

    for ($i = 0; $i <= 10; $i++){
        if ($i % 2 !== 0){ //only if odd numbers
        imagefilledellipse ($image_p, 50 * $i, 50, 100, 100, $color);
        }   

    }

imagejpeg($image_p, uniqid() .'.jpg');

My guess is that in order to tile each circle in a vertical manner it just needs another nested for loop and it would be similar to one already there except the change in y-axis like so :

imagefilledellipse ($image_p, 50, 50 * $i, 100, 100, $color);

I have tried a lot of nesting variation but could not get it to work. Please help.

Tim

The function imagefilledellipse has the following signature (I suppose):

imagefilledellipse(image, x, y, width, height, color)

Which means that you are drawing for every i in 0 < i < 10 a circle with a different x position.

Swap it with the y parameter to draw vertical circles:

$width = 1000; 
$height = 500;

$image_p = imagecreatetruecolor($width, $height); 
$color = imagecolorallocate($image_p, 0, 255, 0); 

    for ($i = 0; $i <= 10; $i++){
        if ($i % 2 !== 0){ //only if odd numbers
        imagefilledellipse ($image_p, 50, 50 * $i, 100, 100, $color);
        }   

    }

imagejpeg($image_p, uniqid() .'.jpg');

In order to draw both horizontal and vertical circles you will need indeed, as you said, a nested for-loop:

$width = 1000; 
$height = 500;

$image_p = imagecreatetruecolor($width, $height); 
$color = imagecolorallocate($image_p, 0, 255, 0); 

    for ($i = 0; $i <= 10; $i++){
        for ($j = 0; $j <= 10; $j++) {
            if ($i % 2 !== 0 && $j % 2 !== 0) { //only if odd numbers
                imagefilledellipse ($image_p, 50 * $i, 50 * $j, 100, 100, $color);
            }   
        }
    }

imagejpeg($image_p, uniqid() .'.jpg');

Also, you do not need to check for odd numbers if you would change the scale from i * 50 to 50 + i * 100, like this:

imagefilledellipse ($image_p, 50 + 100 * $i, 50 + 100 * $j, 100, 100, $color);

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edited at2021-02-22

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