“Is there any way to change the MarkerImage to the featured image for the post?”

Yes, there is!

But one thing to keep in mind is that markers are not one image but two — the marker itself and the shadow. What we’re going to cover here will show how to use the Featured Image as the marker, while continuing to use a single shadow across all posts. This means it is appropriate for markers that share the same size and silhouette.

We’ll be using the code from the previous post as the starting point.

Initiate Featured Images

Create a new file in your theme directory, called functions.php. In it, write:

<?php
 
// Featured Images / Post Thumbnails
if ( function_exists( 'add_theme_support' ) ) {
    add_theme_support( 'post-thumbnails' );
}
 
?>

This is the basic code. For more features see Post Thumbnails in the Codex.

When you go to your Post Edit screen you will now see a metabox called Featured Image. Clicking the link, you will be prompted to upload a file. Once you have done that, click the “Use as featured image” link (it’s next to “Insert into post”).

Make a marker declaration in the loop

We’re going to move our marker declaration into the WordPress loop. We are going to add another parameter to our locations variable, so in index.php look for the line:

info : document.getElementById('item<?php echo $i; ?>')

And place a comma at the end of it.

Because Featured Images are not required by WordPress when publishing a post, we will test if one has been set and to provide a fallback. On the next line include the following test:

<?php if ( has_post_thumbnail() ) { ?>
	// There is a Featured Image
<?php } else { ?>
	// No Featured Image, use fallback
<?php } ?>

And under “use fallback”, define a fallback image

// No Featured Image, use fallback
marker : new google.maps.MarkerImage('<?php echo get_stylesheet_directory_uri() ?>/pink_Marker.png', new google.maps.Size(20, 34) )

Get the path to the Featured Image

The normal way to access the post thumbnail is to use the the_post_thumbnail() function, but this returns a full img tag. We want only the image path, so let’s make our own function that does this. Open functions.php and add:

function get_thumbnail_path($post_ID) {
	$post_image_id = get_post_thumbnail_id($post_ID->ID);
	if ($post_image_id) {
		$thumbnail = wp_get_attachment_image_src( $post_image_id, 'post-thumbnail', false);
		if ($thumbnail) (string)$thumbnail = $thumbnail[0];
		return $thumbnail;
	}	
}

And back in index.php, under the “There is a Featured Image” comment, create a marker declaration that includes a call to the function:

// There is a Featured Image
marker : new google.maps.MarkerImage('<?php echo get_thumbnail_path($post->ID); ?>', new google.maps.Size(20, 34) )

Update the map JavaScript

Last but not least, we’ll modify the maps.js to reflect our changes. Find the line that declares the “pinkmarker”:

var pinkmarker = new google.maps.MarkerImage('/wp-content/themes/mapdemo/pink_Marker.png', new google.maps.Size(20, 34) );

and remove it; it’s no longer needed. Next, look for the line:

icon: pinkmarker,

And change it to:

icon: locations[i].marker,

And that’s it! Save everything and you should now see the featured image loaded as the marker.

Here we will go through the steps for creating a Google Maps interface for a WordPress blog. Posts will appear as markers on the map, which you can click to reveal the post content in the Google Maps Infowindow.

Download a ZIP of the complete example.

I’m starting with a fresh WordPress install, which at the time of this writing is v. 3.3.1. You may be modifying an existing theme, but for the sake of this tutorial, I’ll start a new one. But note that I’ll be doing only the minimum here to create a working demo, omitting much that is necessary for an actual, standards-compliant and useful website.

Add Location Data to Posts

In order to know where to place a marker on a map, the Google Maps API needs to be supplied with latitude and longitude coordinates in the format of a LatLng object. We’re going to include this as a Custom Field with our posts.

Navigate to the Post Edit page and scroll down to the Custom Fields box. (If you don’t see it, you may need to turn it on via the Screen Options button at the top of the page.)

Name the custom field “latlng.” Now, there are various geocoding services on the web that allow you convert an address to latlng (including the Google Maps API itself, but that’s another topic). For this example we’ll use the White House. Go to Geocoder.us and enter “1600 Pennsylvania Avenue NW, Washington DC”. It will spit out a number in brackets such as (38.898748, -77.037684). Use that as the value and press Add Custom Field.

If you like, you can optionally create a few more posts and geocode them with locations in Washington DC.

Update: I’ve published a plugin that simplifies the process of adding location data to posts; Use it instead!

Initialize a Custom Theme

In the wp-content/themes directory, create a new folder; mine will be called mapdemo. In this new folder, create a blank file called style.css and one called index.php; these are the minimum needed to created a WordPress theme. Also create a file called map.js.

To make our theme recognizable by WordPress we will place what’s called a theme header into our style.css. The very minimum header is as follows:

/* 
Theme Name: Map Demo
*/

You can now go ahead and activate your theme using the WordPress dashboard (Appearance -> Themes). But if you load your blog at this point you will see that it’s totally blank. Let’s put in the bare-bones of an HTML page, with a couple of functions required by WordPress. Put the following into index.php:

<html>
	<head>
		<title>Maps Test</title>
		<?php wp_head(); ?>
	</head>
 
	<body>
		<?php wp_footer(); ?>
	</body>
</html>

Link the JavaScript Files

Our map will be created using two JavaScript files: The Google Maps API library and our own maps.js. We do this in the head section of index.php, after the title tag. To include the API we will link directly to the file on Google’s server:

<script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>

And to include maps.js we will do something similar, but you’ll notice that we use WordPress’ get_stylesheet_directory_uri() function to dynamically write the path to the file in our theme directory:

<script type="text/javascript" src="<?php echo get_stylesheet_directory_uri() ?>/map.js"></script>

Create the Map

WordPress uses something called The Loop to display posts. Let’s get that started by testing if, given the parameters passed via the URL, WordPress has any posts to display. In index.php, after the opening body tag, write:

<?php if ( have_posts() ) : ?>
	<!-- WordPress has found matching posts -->
<?php else : ?>
	<!-- No matching posts, show an error -->
	<h1>Error 404 &mdash; Page not found.</h1>
<?php endif; ?>

Next create a DIV element that will be the container for our map; we’ll tell the API its name and Google will fill it with magic! We’ll use CSS to make it fill the window. After the line with the “WordPress has found matching posts” comment, write:

<div id="map" style="width: 100%; height: 100%;"></div>

Now open up maps.js. We’re going to create a JavaScript function that loads in a map with a few settings, which I won’t go into the details of here, but are well documented. Write:

function initialize() {
	map = new google.maps.Map(document.getElementById('map'), { 
		zoom: 12, 
		center: new google.maps.LatLng(38.898748, -77.037684), 
		mapTypeId: google.maps.MapTypeId.ROADMAP 
	});
}

But, like all functions, it’s not enough to define it — it must also be called. We’ll do this by modifying the body tag of index.php, like so:

<body onload="initialize()">

Reload your page and you should now see a map filling the window, centred on Washington DC.

Place the Markers

The way we’re going to get our markers onto the map is to:

1. create a list (an array) of locations;
2. specify the images we’re going to place at those locations;
3. then go through (iterate) through the list, placing each one.

First up, the locations. We’re going to finish up that WordPress loop we started, where for each post we output an item in an array called “locations.” At this point we’re going to output only our “latlng” custom field, not the post title or content or any of the others. In index.php, right above the div with the ID of “map”, write this:

<script type="text/javascript">
	var locations = [
		<?php  $i = 1; while ( have_posts() ) : the_post(); ?>
			<?php if ( get_post_meta($post->ID, 'latlng', true) !== '' ) : ?>
				{
					latlng : new google.maps.LatLng<?php echo get_post_meta($post->ID, 'latlng', true); ?>, 
				},
			<?php endif; ?>
		<?php $i++; endwhile; ?>
	];
</script>

Next we’ll define the images we want to use as markers. Each marker has two parts — the marker itself and its shadow, and for each you will supply paths to images of your choosing; I’ve included a couple in the ZIP, linked above, or you can use your own. Upload the images into your theme folder. At the very top of maps.js, above the initialize function, write:

var pinkmarker = new google.maps.MarkerImage('/wp-content/themes/mapdemo/pink_Marker.png', new google.maps.Size(20, 34) );
var shadow = new google.maps.MarkerImage('/wp-content/themes/mapdemo/shadow.png', new google.maps.Size(37, 34) );

If you are using your own images you will want to check Google’s documentation of the MarkerImage options to see what each part of these lines mean, so that you can customize them.

Note: I’ve created a follow-up post on using the post’s Featured Image as the marker.

And the final step is to loop through the locations, placing a marker for each onto the map. In maps.js, within the “initialize” function, after the “var map…” block, write:

for (var i = 0; i < locations.length; i++) {  
	var marker = new google.maps.Marker({
    	position: locations[i].latlng,
		icon: pinkmarker,
		shadow: shadow,
		map: map
	});
}

Reload your page and you should now see your marker(s) placed on the map.

Enable the Infowindow

Our last task is to create a Google Maps “infowindow” which will pop-up when a marker is clicked, showing the title and content of the post. We will do this by:

1. outputting the content into a hidden div;
2. referencing that div in our array of locations;
3. and adding what’s known as a “click listener” to our JavaScript function to open the window.

First up, the content. This will be a a second “while” loop, immediately before the one we wrote previously. It will output a series of DIVs, each with a unique ID and containing content to be shown in the infowindow. In index.php, directly following the “matching posts” comment line, write:

<div style="display: none;">
	<?php $i = 1; ?>
	<?php while ( have_posts() ) : the_post(); ?>
		<?php if ( get_post_meta($post->ID, 'latlng', true) !== '' ) : ?>
			<div id="item<?php echo $i; ?>">
				<p><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></p>
				<?php the_content(); ?>
			</div>
		<?php endif; ?>
		<?php $i++;	?>
	<?php endwhile; ?>
</div>

Next add a reference to these DIVs to our locations object. Directly after this line:

latlng : new google.maps.LatLng<?php echo get_post_meta($post->ID, 'latlng', true); ?>,

Add this:

info : document.getElementById('item<?php echo $i; ?>')

Now define the infowindow (documentation at Google). Switch over to maps.js and, at the very top, write this:

var infowindow = new google.maps.InfoWindow();

Finally, add a click listener for each marker. Within the “for…” block of the “initialize” function, after the “var marker…” block, write:

google.maps.event.addListener(marker, 'click', (function(marker, i) {
  return function() {
    infowindow.setContent(locations[i].info);
    infowindow.open(map, marker);
  }
})(marker, i));

And that’s it! Reload the page and you will now be able to click the marker(s), opening up an infowindow containing the post content. Mission accomplished!

The technique applied on Seth Anderson’s photo site.

You can preview the code here.

“Any” & “And” Tag Intersections

By passing parameters via the URL, WordPress will create pages for the intersections of multiple tags. This means we can get posts with any of the tags by separating terms with a comma, like so: /?tag=onetag,anothertag. That is to say a post must have one but need not have all of the tags to qualify.

Conversely, we can get posts with all of the tags by separating terms with a plus, like so: /?tag=onetag+anothertag. This will return only posts that have every tag. There’s various issues with the default output of this, however, so go ahead and install the tTDO Tag Fixes plugin. Running this plugin changes the “all” URL string to /?tdo_tag=onetag+anothertag.

Show All Tags

The first thing we’ll do is print out all the tags, with links, onto the page. This goes in your theme’s functions.php:

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function showalltags() {
 
	$my_query = new WP_Query('posts_per_page=1');
 
	while ($my_query->have_posts()) : $my_query->the_post();
 
	$tags = get_tags();
	$html;
	foreach ($tags as $tag){
		$tag_link = get_tag_link($tag->term_id);
 
		$html .= "<a href='{$tag_link}' title='{$tag->name} Tag' class='{$tag->slug}'>";
		$html .= "{$tag->name}</a>";
	}
	echo $html;
 
	endwhile;
 
}

And output it somewhere in your theme like so:

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<div class="taxonomies">
	<h3 id="tags">Tags</h3>
	<div class="taglist"><?php showalltags(); ?></div>
</div>

Rewrite the markup

Now we’re going to use JavaScript to update the page’s markup to reflect the JavaScript-dependent functionality we’re building. We do this with JS because these controls are only relevant to users with JS-enabled browsers — for others their presence would only be confusing.

Get your jQuery(document).ready(function($) started then include this:

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function initialLoad () {
	$('.taxonomies h3').html('Select one or more tags, then press <em>&ldquo;Search Tags&rdquo;</em>');
	$('.taglist').before('<div class="searchcontrols"><span>Find photos with </span><a id="any" class="tagtoggle selected">any</a><span class="slash"> / </span><a id="all" class="tagtoggle">all</a><span> of the selected criteria</span>');	
	$('.taxonomies').append('<a class="searchtags">Search Tags</a></div>');	
}
 
initialLoad();

Capture tag clicks

When a user clicks a tag, we’ll override the link and instead add the class “selectedtag”:

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$('.taglist a').bind('click', function(event) {
	event.preventDefault();
 
	if ( $(this).hasClass('selectedtag') ) {
		$(this).removeClass('selectedtag');
	} else {
		$(this).addClass('selectedtag');
	}
 
});

Toggle “Any” & “And”

Similarly, capture clicks to the controls:

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$('.tagtoggle').bind('click', function(event) {
	event.preventDefault()
	$('.tagtoggle').removeClass('selected');
	$(this).addClass('selected');
});

Construct the URL

This function is the core of the mechanism:

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function searchTags() {
	var optionTexts = [];
 
	// For each selected tag...
	$('.selectedtag').each(function() { 
 
		// capture the slug from class (stripping out the " selectedtag")
		var str = $(this).attr('class').replace(/\sselectedtag+/g, '');
 
		// and add it to an array
		optionTexts.push(str);
	});	
 
	// Set the URL format appropriate to the selected search type
	if ( $('#any').hasClass('selected') ) {
		var param = 'tag';
		var separator = ',';
	} else {
		var param = 'tdo_tag';
		var separator = '+';			
	}
 
	// Put the tag list together
	var tagstring = optionTexts.join(separator);
 
	// And send them off to the final, constructed URL
	window.location = '/?' + param + '=' + tagstring;
 
}

Enable the Search Button

Last but not least, the action on the search button calls the search function:

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$('.searchtags').bind('click', function(event) {
	event.preventDefault()
	searchTags();
});

And that’s it! You can take a look at the full JavaScript in context here.

Updated 12/10/11 to capture the tag slug from the class, rather than inferring it from the tag name.

An interface to display short video clips in a gallery setting.

In 2009 artist Midi Onodera created a series of 52 short clips designed for podcasting. I have been fortunate to be involved in this project, providing technical support and new media development. When exhibition opportunities arise, such as Onodera’s recent show at Concordia University in Montreal, we grapple with ways to present these new-media-specific works in the gallery setting. Knowing Concordia had some sweet gear, Onodera chose show this series on a large touch-screen monitor. I designed and implemented the interface using web-standard technologies including jQuery and HTML5 Video.

I have posted the code on Github. It uses a version of the jQuery vertical center function I previously posted, as well as some other interface effects. One of my favourite of its features is the randomization: The thumbnails are shuffled as the page is loaded and then each moves to the end of the page upon being selected. At its core are the functions to load and play the clips.

Swapping Sources in an HTML 5 Video

The interface provides access to 53 video clips, but rather than giving each its own instance, I set up an single video element, omitting a source.

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<video class="video" id="video" controls="" autoplay="" width="640" height="426"></video>

And then, when a video is selected, its source is added in and the element begins to play.

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$('.video').attr('src','movies/' + movieNum + '.m4v');
document.getElementById('video').play();

But the strangest thing happened when the next video is loaded and played: The audio from the first clip would play along with the new! I tried all sorts of things, including completely unloading the video element and creating a new one for each cycle, but still the audio could be heard. What a strange bug!

In the end I found it could be solved by, upon closing the clip, pausing the playback and then removing the video source:

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document.getElementById('video').pause();
$('.video').removeAttr('src');

All of this can be seen in-context over at Github.

Playing a video.

The touch-screen rig.

It’s pretty straightforward, but note line 4. On one of the sites I used this on the centered element needed to appear in the middle of the field under a top navigation bar, so this looks for that element and factors that into the calculation.

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jQuery.fn.center = function () {
 
	var $t = ( ( $(window).height() - this.outerHeight() ) / 2);
	var $h = $('.header').outerHeight();
 
      	if ( ( $(window).height() - $h ) >= this.outerHeight() ) {
		jQuery('.shade').fillWindow();
 
    		this.css({ "position":"fixed","top" : ($t + "px") });
 
		if ( $(window).width() >= this.outerWidth() ) {
    			this.css("left", (($(window).width() - this.outerWidth()) / 2) + $(window).scrollLeft() + "px");
		}
 
	} else {
		// Don't do
	}
 
	this.show();
 
   	return this;
 
}

And then use it like this:

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$('.someElement').center();

Also, do remember to use this only once all the elements have loaded. It’ll come out wrong if you center before, for instance, all the images have come in. So make sure the element is at its full dimensions before you fire this.