Source

File: wp-admin/includes/class-custom-image-header.php

public function step_2() {
		check_admin_referer( 'custom-header-upload', '_wpnonce-custom-header-upload' );
		if ( ! current_theme_supports( 'custom-header', 'uploads' ) ) {
			wp_die(
				'<h1>' . __( 'Something went wrong.' ) . '</h1>' .
				'<p>' . __( 'The current theme does not support uploading a custom header image.' ) . '</p>',
				403
			);
		}

		if ( empty( $_POST ) && isset( $_GET['file'] ) ) {
			$attachment_id = absint( $_GET['file'] );
			$file          = get_attached_file( $attachment_id, true );
			$url           = wp_get_attachment_image_src( $attachment_id, 'full' );
			$url           = $url[0];
		} elseif ( isset( $_POST ) ) {
			$data          = $this->step_2_manage_upload();
			$attachment_id = $data['attachment_id'];
			$file          = $data['file'];
			$url           = $data['url'];
		}

		if ( file_exists( $file ) ) {
			list( $width, $height, $type, $attr ) = @getimagesize( $file );
		} else {
			$data   = wp_get_attachment_metadata( $attachment_id );
			$height = isset( $data['height'] ) ? $data['height'] : 0;
			$width  = isset( $data['width'] ) ? $data['width'] : 0;
			unset( $data );
		}

		$max_width = 0;
		// For flex, limit size of image displayed to 1500px unless theme says otherwise.
		if ( current_theme_supports( 'custom-header', 'flex-width' ) ) {
			$max_width = 1500;
		}

		if ( current_theme_supports( 'custom-header', 'max-width' ) ) {
			$max_width = max( $max_width, get_theme_support( 'custom-header', 'max-width' ) );
		}
		$max_width = max( $max_width, get_theme_support( 'custom-header', 'width' ) );

		// If flexible height isn't supported and the image is the exact right size.
		if ( ! current_theme_supports( 'custom-header', 'flex-height' ) && ! current_theme_supports( 'custom-header', 'flex-width' )
			&& get_theme_support( 'custom-header', 'width' ) == $width && get_theme_support( 'custom-header', 'height' ) == $height ) {
			// Add the metadata.
			if ( file_exists( $file ) ) {
				wp_update_attachment_metadata( $attachment_id, wp_generate_attachment_metadata( $attachment_id, $file ) );
			}

			$this->set_header_image( compact( 'url', 'attachment_id', 'width', 'height' ) );

			/**
			 * Fires after the header image is set or an error is returned.
			 *
			 * @since 2.1.0
			 *
			 * @param string $file          Path to the file.
			 * @param int    $attachment_id Attachment ID.
			 */
			do_action( 'wp_create_file_in_uploads', $file, $attachment_id ); // For replication.

			return $this->finished();
		} elseif ( $width > $max_width ) {
			$oitar = $width / $max_width;
			$image = wp_crop_image( $attachment_id, 0, 0, $width, $height, $max_width, $height / $oitar, false, str_replace( wp_basename( $file ), 'midsize-' . wp_basename( $file ), $file ) );
			if ( ! $image || is_wp_error( $image ) ) {
				wp_die( __( 'Image could not be processed. Please go back and try again.' ), __( 'Image Processing Error' ) );
			}

			/** This filter is documented in wp-admin/includes/class-custom-image-header.php */
			$image = apply_filters( 'wp_create_file_in_uploads', $image, $attachment_id ); // For replication.

			$url    = str_replace( wp_basename( $url ), wp_basename( $image ), $url );
			$width  = $width / $oitar;
			$height = $height / $oitar;
		} else {
			$oitar = 1;
		}
		?>

<div class="wrap">
<h1><?php _e( 'Crop Header Image' ); ?></h1>

<form method="post" action="<?php echo esc_url( add_query_arg( 'step', 3 ) ); ?>">
	<p class="hide-if-no-js"><?php _e( 'Choose the part of the image you want to use as your header.' ); ?></p>
	<p class="hide-if-js"><strong><?php _e( 'You need JavaScript to choose a part of the image.' ); ?></strong></p>

	<div id="crop_image" style="position: relative">
		<img src="<?php echo esc_url( $url ); ?>" id="upload" width="<?php echo $width; ?>" height="<?php echo $height; ?>" alt="" />
	</div>

	<input type="hidden" name="x1" id="x1" value="0"/>
	<input type="hidden" name="y1" id="y1" value="0"/>
	<input type="hidden" name="width" id="width" value="<?php echo esc_attr( $width ); ?>"/>
	<input type="hidden" name="height" id="height" value="<?php echo esc_attr( $height ); ?>"/>
	<input type="hidden" name="attachment_id" id="attachment_id" value="<?php echo esc_attr( $attachment_id ); ?>" />
	<input type="hidden" name="oitar" id="oitar" value="<?php echo esc_attr( $oitar ); ?>" />
		<?php if ( empty( $_POST ) && isset( $_GET['file'] ) ) { ?>
	<input type="hidden" name="create-new-attachment" value="true" />
	<?php } ?>
		<?php wp_nonce_field( 'custom-header-crop-image' ); ?>

	<p class="submit">
		<?php submit_button( __( 'Crop and Publish' ), 'primary', 'submit', false ); ?>
		<?php
		if ( isset( $oitar ) && 1 == $oitar && ( current_theme_supports( 'custom-header', 'flex-height' ) || current_theme_supports( 'custom-header', 'flex-width' ) ) ) {
			submit_button( __( 'Skip Cropping, Publish Image as Is' ), '', 'skip-cropping', false );
		}
		?>
	</p>
</form>
</div>
		<?php
	}