Question

I am writing PHP script, which will store mouse position over the page with a timestamp. It will be used for generating simple heatmap.
I have MySQL database of X & Y coordinates and I thought, that I would do an array, which I would use for adding counts of appearances of the cursor over specific pixel.
It would work like this:
I read data from the database saying for example four recordings (x/y) 10/9,8/7,2/10,10/9
I would put 1 on each of the coordinates in the array, the last point would already in the array, so it would put 2 on x=10/y=9, as total count of mouse being over that pixel.

How should I make the array and how to read it?

Answer 1

First, you need to create an empty matrix, where the entire grid is defined and populated with zeros:

$width = 10;
$height = 10;

$matrix = array_fill(1, $height, array_fill(1, $width, 0));

Now you simply iterate over your MySQL results and increment each associated point every time you hit it. In this example I assume your x and y columns are just called x and y.

while ($row = mysql_fetch_assoc($queryResult)) {
  $matrix[$row['y']][$row['x']]++;
}

Now if you want to get the number of hits for the point where e.g. x = 1, y = 8, you simply do:

$hits = $matrix[8][1];

You can swap the levels round so x is on the outer level so they can be referenced as $matrix[$x][$y] instead of $matrix[$y][$x] if you wish, but I personally feel it makes more sense if the array is structured as rows of columns (ys of xs) like a database table.