Displaying/outputting a simple map

[spence911]

This script is an exercise that i got from a text book. It simulates the path of a homing pigeon as it flies from its starting point to its home. The script is easy to comprehend. The only problem i have is the block of code that displays the map as I've highlighted below.

<?php

$mapsize = 10;

// Position the home and the pigeon

do{
$homeX = rand (0, $mapsize-1);
$homeY = rand (0, $mapsize-1);
$pigeonX = rand(0, $mapsize-1);
$pigeonY = rand(0, $mapsize-1);
} while ((abs($homeX-$pigeonX) < $mapsize/2) && (abs($homeY-$pigeonY) < $mapsize/2));

do{

// Move the pigeon closer to home

if ($pigeonX < $homeX)
$pigeonX++;
elseif ($pigeonX > $homeX)
$pigeonX--;

if ($pigeonY < $homeY)
$pigeonY++;
elseif ($pigeonY > $homeY)
$pigeonY--;

// Display the current map

echo '<div class="map" style="width: ' . $mapsize . 'em;"><pre>';

for ($y = 0; $y < $mapsize; $y++){
for ($x = 0; $x < $mapsize; $x++){
if ($x == $homeX AND $y == $homeY){
echo '<span class ="home">+</span>'; // Home
} elseif ($x == $pigeonX && $y == $pigeonY) {
echo '<span class ="pigeon">%</span>'; // Pigeon
} else {
echo '<span class = "empty">.</span>'; //Empty square
}
echo ($x != $mapsize - 1) ? " " : " ";
}
echo "\n";
}
echo "</pre></div>\n";
} while ($pigeonX != $homeX || $pigeonY != $homeY);

?>

</body>
</html>

How does this line affect the map? I have never come across the "?" and ":" operators, moreover the use of echo in this fashion.

echo ($x != $mapsize - 1) ? " " : " ";

[Barand]

See "Ternary operator" on this page http://php.net/manual/en/language.operators.comparison.php

 

Basically

echo (condition) ? 'A' : 'B';

is shorthand for

if (condition == true) {
    echo 'A';
} else {
    echo 'B';
}

In your code it is useless as it echos the same value regardless of the test.

[Ch0cu3r]

IGNORE

Edited November 4, 2013 by Ch0cu3r

[spence911]

@Barand. The code is actually very useful in displaying the map. As is - It outputs a series of 10 dots across the y-axis of the map even if there are no values inside the quotations.

[Ch0cu3r]

 

@Barand. The code is actually very useful in displaying the map.

The line with the ternary operator is useless as it just echo's a space no matter what.  You could simply replace it with   echo " "; and you'll get the same result.

[Barand]

I've done a graphical version for you to play with (attached) which creates an image.

 

Place on a page with an ordinary HTML image tag

<img src='pigeon.php' width='500' height='500' alt='pigeon'/>

pigeon.php

Edited November 4, 2013 by Barand

[spence911]

I was really looking forward to playing with that code Barand. I created a pigeon.php, dropped that image tag into a seperate file, saved it and when i opened it the output it generated was just an empty frame with no image.

[Ch0cu3r]

Remove the first two lines (2 and 3) from pigeon.php. The database connection is not needed.

[spence911]

Remove the first two lines (2 and 3) from pigeon.php. The database connection is not needed.

I just removed both lines and still not working. All I'm getting is a box with a missing image :[

[Ch0cu3r]

Change lines 26 - 33 from a while loop to a do-while loop

do {
    $px = floor(rand ($px1, $homeX)/10)*10;
    $py = floor(rand ($py1, $homeY)/10)*10;
    imageline($im, $px1, $py1, $px, $py, $rte);
    imagefilledellipse($im, $px, $py, 5, 5, $wht);
    $px1 = $px;
    $py1 = $py;
} while ($px != $homeX && $py != $homeY);

[spence911]

IGNORE

Edited November 5, 2013 by spence911

[spence911]

 

Change lines 26 - 33 from a while loop to a do-while loop

do {
    $px = floor(rand ($px1, $homeX)/10)*10;
    $py = floor(rand ($py1, $homeY)/10)*10;
    imageline($im, $px1, $py1, $px, $py, $rte);
    imagefilledellipse($im, $px, $py, 5, 5, $wht);
    $px1 = $px;
    $py1 = $py;
} while ($px != $homeX && $py != $homeY);

Awesome! I think this is a great example to wrap my head around image mapping with. Much appreciated.

[Barand]

Remove the first two lines (2 and 3) from pigeon.php. The database connection is not needed.

Sorry about those 2 lines, I have those automatically in my php files as nearly all are DB related.

 

Are pigeon.php and the file with the image tag in the same folder - it was definitely working when it left the factory. (sample attached)

[spence911]

Sorry about those 2 lines, I have those automatically in my php files as nearly all are DB related.

 

Are pigeon.php and the file with the image tag in the same folder - it was definitely working when it left the factory. (sample attached)

 

Yes I did finally get it to work thanks to the edits by Ch0cu3. Awesome script btw, very practical, definitely gonna enjoy it.