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Displaying/outputting a simple map


Go to solution Solved by Ch0cu3r,

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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) ? " " : " ";
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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.

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 by Barand
  • Solution

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);

 

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.

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)

post-3105-0-21823100-1383686955_thumb.png

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.

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