PHP GD basic rectangle offset maths - php

Question

I'm completely stuck with something that i believe is relatively simple to solve:
In PHP I am drawing filled rectangles on top of an image (using GD) - I want a small gap between each of them - which is specified in the code (gap is the same for each box) - I loop around until i've hit the max amount of rectangles on a row (e.g max columns) - and i've managed the horizontal gap offset but for the life of me can't work out the vertical gap maths.
Here is my code in it's nasty entirety:
http://pastebin.com/MHUqi0tG
But specifically PHP accepts two sets of coordinates to make a rectangle - two for the top left (x and y) and two for the bottom right (x and y).
Here is my code for that in particular:
$left_wall_of_box_x = ( $current_col * $box_size ) + $origin_x ;
if($last_block_x != $origin_x){
$left_wall_of_box_x = $last_block_x + $gap;
}
/*verticals coord 1*/
$left_wall_of_box_y = ( $current_row * $box_size ) + $origin_y;
$right_wall_x = $left_wall_of_box_x + $box_size ;
$right_wall_y = $left_wall_of_box_y + $box_size;
imagefilledrectangle($im, $left_wall_of_box_x, $left_wall_of_box_y, $right_wall_x, $right_wall_y, $red);
$gap = 2;
$origin_x & origin_y = the place i start drawing boxes from.
Output at the moment is nicely separated boxes on the horizontal axis but vertically they are hitting each other/merging together.
Any help obviously greatly appreciated - Tearing hair out on this.
Thanks

Answer 1

The mistake is here:
$left_wall_of_box_y = ( $current_row * $box_size ) + $origin_y;
Should be:
$left_wall_of_box_y = ( $current_row * ($box_size + $gap_vertical)) + $origin_y;
But your code is fragile and hard to read. It's fragile as you're making your calculations more be dependent on variables that represent subtly different things, and as there's more variables, it's harder to fit in your head - which is partly why you didn't spot the error.
So, rather than doing this:
while($x <= $total_boxes_to_draw)
{
if($current_col >= $cols)
{
//reset to start of row
}
}
Write your code like this.
$finished = false;
for ($y=0; ($y<$rows) && ($finished==false) ; $y++)
{
$yPosition = $origin_y + $y * ($box_size + $spacing_vertical);
for ($x=0 ; $x<$cols && ($finished==false) ; $x++)
{
$xPosition = $origin_x + $x * ($box_size + $spacing_horizontal);
//draw box at $xPosition, $yPosition
$boxesDrawn++;
if ($boxesDrawn >= $total_boxes_to_draw){
$finished = true;
}
}
}

Answer 2

You are adding a gap horizontally, but you also have to add it vertically.
A simple fix is subtracting the gap from the height of the rectangles you fill:
imagefilledrectangle($im, $left_wall_of_box_x, $left_wall_of_box_y,
$right_wall_x, $right_wall_y - gap, $red);