How do I nest this for loop? - php

Question

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.

Answer 1

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);

Answer 2

If you know how many columns you want it should be quite easy.
$colCounter=0;
$yAxis = 50;
for ($i = 0; $i <= 10; $i++){
if ($i % 2 !== 0){ //only if odd numbers
if ($colCounter % 5 === 0){ // Do something every 5 cols
$yAxis = $yAxis + 50 // add 50 onto each row
}
$colCounter++;//increment counter
imagefilledellipse ($image_p, 50 * $i, $yAxis, 100, 100, $color);
}
}
Note this is un-tested code