<?php

/**
 * Auto Fit Text To Image
 *
 * Write text to image using a target width, height, and starting font size. 
 * 
 * @author Clif Griffin
 * @url http://cgd.io/2014/auto-fit-text-to-an-image-with-php-and-wordpress
 *
 * @access public
 * @param bool $canvas_image_filename (default: false) The base image.
 * @param string $dest_filename (default: 'output.jpg') The output filename.
 * @param string $text (default: '') The text being written.
 * @param int $starting_font_size (default: 60) The starting (max) font size.
 * @param int $max_height (default: 500) The maximum height in lines of text.
 * @param int $x_pos (default: 0) X position in pixels for first line of text.
 * @param int $y_pos (default: 0) Y position in pixels for first line of text.
 * @param bool $font_file (default: false) Path to font file (.ttf)
 * @param string $font_color (default: 'black') The color. Also accepts rgba values. Example: "rgba(0,0,0,0.5)"
 * @param int $line_height_ratio (default: 1) Allows scaling the line height. Should be between 0.1 and 1.
 * @param string $dest_format (default: 'jpg') Output format.
 * @return bool True: success, False: failure
 */
function autofit_text_to_image( $canvas_image_filename = false, $dest_filename = 'output.jpg', $text = '', $starting_font_size = 60, $max_width = 500, $max_height = 500, $x_pos = 0, $y_pos = 0, $font_file = false, $font_color = 'black', $line_height_ratio = 1, $dest_format = 'jpg' ) {
	// Bail if any essential parameters are missing
	if ( ! $canvas_image_filename || ! $dest_filename || empty($text) || ! $font_file || empty($font_color) || empty($max_width) || empty($max_height) ) return false;
	
	// Do we have a valid canvas image?
	if ( ! file_exists($canvas_image_filename) ) return;
	
	$canvas_handle = fopen( $canvas_image_filename, 'rb' );
	
	// Load image into Imagick
	$NewImage = new Imagick();
	$NewImage->readImageFile($canvas_handle);
	
	// Instantiate Imagick utility objects
	$draw = new ImagickDraw();
	$pixel = new ImagickPixel( $font_color );
	
	// Load Font 
	$font_size = $starting_font_size;
	$draw->setFont($font_file);
	$draw->setFontSize($font_size);
	
	// Holds calculated height of lines with given font, font size
	$total_height = 0;
	
	// Run until we find a font size that doesn't exceed $max_height in pixels
	while ( 0 == $total_height || $total_height > $max_height ) {
		if ( $total_height > 0 ) $font_size--; // we're still over height, decrement font size and try again
		
		$draw->setFontSize($font_size);
		
		// Calculate number of lines / line height
		// Props users Sarke / BMiner: http://stackoverflow.com/questions/5746537/how-can-i-wrap-text-using-imagick-in-php-so-that-it-is-drawn-as-multiline-text
		$words = preg_split('%\s%', $text, -1, PREG_SPLIT_NO_EMPTY);
		$lines = array();
		$i = 0;
		$line_height = 0;
	
		while ( count($words) > 0 ) { 
			$metrics = $NewImage->queryFontMetrics( $draw, implode(' ', array_slice($words, 0, ++$i) ) );
			$line_height = max( $metrics['textHeight'], $line_height );
	
			if ( $metrics['textWidth'] > $max_width || count($words) < $i ) {
				$lines[] = implode( ' ', array_slice($words, 0, --$i) );
				$words = array_slice( $words, $i );
				$i = 0;
			}
		}
		
		$total_height = count($lines) * $line_height * $line_height_ratio;
		
		if ( $total_height === 0 ) return false; // don't run endlessly if something goes wrong
	}
	
	// Writes text to image
	for( $i = 0; $i < count($lines); $i++ ) {
		$NewImage->annotateImage( $draw, $x_pos, $y_pos + ($i * $line_height * $line_height_ratio), 0, $lines[$i] );	
	}
	
	$NewImage->setImageFormat($dest_format);
	$result = $NewImage->writeImage($dest_filename);
	
	return $result;
}

<?php
// autofit_text_to_image() example
// http://cgd.io/2014/auto-fit-text-to-an-image-with-php-and-wordpress

$canvas_image_filename = 'quote_canvas.png';
$dest_filename = 'quote.jpg';
$text = 'I believe in pink. I believe that laughing is the best calorie burner. I believe in kissing, kissing a lot.';
$font_file = 'Cedarville-Cursive.ttf';

autofit_text_to_image($canvas_image_filename, $dest_filename, $text, 60, 500, 400, 40, 400, $font_file);

<?php
// autofit_text_to_image() WordPress example
// http://cgd.io/2014/auto-fit-text-to-an-image-with-php-and-wordpress

$canvas_image_filename = 'quote_canvas.png';
$dest_filename = trailingslashit($upload_dir['path']) . "featured_image_{$post->ID}.jpg";
$text = 'I believe in pink. I believe that laughing is the best calorie burner. I believe in kissing, kissing a lot.';
$font_file = 'Cedarville-Cursive.ttf';

$result = autofit_text_to_image($canvas_image_filename, $dest_filename, $text, 60, 500, 400, 40, 400, $font_file);

if ($result) {
	$upload_dir = wp_upload_dir();
	$filetype = wp_check_filetype( basename( $dest_filename ), null );
		
	$attachment = array(
		'guid'           => $upload_dir['url'] . '/' . basename( $dest_filename ), 
		'post_mime_type' => $filetype['type'],
		'post_title'     => preg_replace( '/\.[^.]+$/', '', basename( $dest_filename ) ),
		'post_content'   => '',
		'post_status'    => 'inherit'
	);

	$new_attachment = wp_insert_attachment( $attachment, $dest_filename, $post->ID );
	$attach_data = wp_generate_attachment_metadata( $new_attachment, $dest_filename );
	wp_update_attachment_metadata( $new_attachment,  $attach_data );
		
	update_post_meta($post->ID, '_thumbnail_id', $new_attachment);
}