Making post-thumbnail a background image - php

Question

My Wordpress site displays all the posts, stacked in articles spanning the full width on the index.php using rows (Bootstrap 3).
index.php - HTML
<div>
<?php if ( have_posts() ) : ?>
<?php /* Start the Loop */ ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php
get_template_part( 'content' );
?>
<?php endwhile; ?>
<div class="clearfix"></div>
<div class="col-md-12">
</div>
<?php else : ?>
<?php get_template_part( 'no-results', 'index' ); ?>
<?php endif; ?>
</div>
content.php displays the post in each article (which are stacked on top of each other, full width, down the page)
<article id="post-<?php the_ID(); ?>" <?php post_class('container-fluid'); ?>>
<div class="row">
<div class="col-md-12 horiz-cell">
<h2><?php the_title(); ?></h2>
<?php the_category(', '); ?>
</div>
</div>
</article><!-- /#post -->
I have the title and category showing up properly in each row. I would like each post's post-thumbnail (I added its use in functions.php) to be the background image of each row. Filling the whole space (background-size: cover)
Basically large, '100% width' & '300px(roughly) height' rows, each with corresponding title, category, and their post-thumbnail as a background-image.

Answer 1

If not done yet, enable thumbnails and define custom image sizes:
// Enable thumbnails
add_theme_support( 'post-thumbnails' );
add_image_size('my-fun-size',580, 480, true);
To display the thumbnails:
First, get the featured image URL for the post:
The parameter 'my-fun-size' should be the name of the size of the image you defined in your functions.php file - it can also be 'full' or 'thumbnail'
<?php
if (has_post_thumbnail()) {
$thumbnail_data = wp_get_attachment_image_src( get_post_thumbnail_id( get_the_ID() ), 'my-fun-size' );
$thumbnail_url = $thumbnail_data[0];
}
?>
Then add the image as a background:
<article id="post-<?php the_ID(); ?>" style="background-image:url('<?php echo $thumbnail_url ?>')" <?php post_class('container-fluid'); ?> >
<div class="row">
<div class="col-md-12 horiz-cell">
<h2><?php the_title(); ?></h2>
<?php the_category(', '); ?>
</div>
</div>
</article><!-- /#post -->
And finally, apply some CSS to achieve your desired background-size:
article {
background-size: cover;
}

Answer 2

It sounds like you've already figured out the CSS part, so here's the PHP/HTML you're looking for:
<article id="post-<?php the_ID(); ?>" <?php post_class('container-fluid'); ?>>
<?php $imgurl = wp_get_attachment_src( get_post_thumbnail_id($post->ID) ); ?>
<div class="row" style="background-image: url('<?php echo $imgurl[0]; ?>');">
<div class="col-md-12 horiz-cell">
<h2><?php the_title(); ?></h2>
<?php the_category(', '); ?>
</div>
</div>
</article><!-- /#post -->
References:
http://codex.wordpress.org/Function_Reference/get_post_thumbnail_id
http://codex.wordpress.org/Function_Reference/wp_get_attachment_image_src