wordpress从顶部开始裁剪图片的方法

Mike

wordpress默认情况下，裁剪的图片会直接裁剪图片的中间部分，例如你上传了一张美女图片，上传上去由于图片的尺寸超出了内部规定的尺寸，wordpress会对其进行裁剪，按照规定的尺寸裁剪好后生成另外一张图片进行保存，可惜的是，当你调用这张图片的时候发现，美女的头被卡擦了，这样的缩略图完全失去了吸引读者的功效，下面我们就来解决这个问题

代码如下:

<?php
/* Example Usage:
 * bt_add_image_size( 'product-screenshot', 300, 300, array( 'left', 'top' ) );
 * bt_add_image_size( 'product-feature', 460, 345, array( 'center', 'top' ) );
 */
 
add_filter( 'intermediate_image_sizes_advanced', 'bt_intermediate_image_sizes_advanced' );
add_filter( 'wp_generate_attachment_metadata', 'bt_generate_attachment_metadata', 10, 2 );
 
/**
 * Registers a new image size with cropping positions
 *
 * The $crop parameter works as in the 'add_image_size' function taking true or
 * false values. If set to true, the default cropping position is 'center', 'center'.
 * 
 * The $crop parameter also takes an array of the format
 * array( x_crop_position, y_crop_position )
 * x_crop_position can be 'left', 'center', 'right'
 * y_crop_position can be 'top', 'center', 'bottom'
 * 
 * @param string $name Image size identifier.
 * @param int $width Image width.
 * @param int $height Image height.
 * @param bool|array $crop Optional, default is false. Whether to crop image to specified height and width or resize. An array can specify positioning of the crop area.
 * @return bool|array False, if no image was created. Metadata array on success.
 */
function bt_add_image_size( $name, $width = 0, $height = 0, $crop = false ) {
  global $_wp_additional_image_sizes;
  $_wp_additional_image_sizes[$name] = array( 'width' => absint( $width ), 'height' => absint( $height ), 'crop' => $crop );
}
 
 
/**
 * Returning no sizes (an empty array) will force
 * wp_generate_attachment_metadata to skip creating intermediate image sizes on
 * upload, then we can run our own resizing functions by hooking into the
 * 'wp_generate_attachment_metadata' filter
 */
function bt_intermediate_image_sizes_advanced( $sizes ) {
  return array();
}
 
 
function bt_generate_attachment_metadata( $metadata, $attachment_id ) {
  $attachment = get_post( $attachment_id );
  
  $uploadPath = wp_upload_dir();
  $file = path_join($uploadPath['basedir'], $metadata['file']);
 
  if ( !preg_match('!^image/!', get_post_mime_type( $attachment )) || !file_is_displayable_image( $file ) ) return $metadata;
 
  global $_wp_additional_image_sizes;
 
  foreach ( get_intermediate_image_sizes() as $s ) {
    $sizes[$s] = array( 'width' => '', 'height' => '', 'crop' => FALSE );
    if ( isset( $_wp_additional_image_sizes[$s]['width'] ) )
      $sizes[$s]['width'] = intval( $_wp_additional_image_sizes[$s]['width'] ); // For theme-added sizes
    else
      $sizes[$s]['width'] = get_option( "{$s}_size_w" ); // For default sizes set in options
    if ( isset( $_wp_additional_image_sizes[$s]['height'] ) )
      $sizes[$s]['height'] = intval( $_wp_additional_image_sizes[$s]['height'] ); // For theme-added sizes
    else
      $sizes[$s]['height'] = get_option( "{$s}_size_h" ); // For default sizes set in options
    if ( isset( $_wp_additional_image_sizes[$s]['crop'] ) )
      $sizes[$s]['crop'] = $_wp_additional_image_sizes[$s]['crop'];
    else
      $sizes[$s]['crop'] = get_option( "{$s}_crop" );
  }
 
  foreach ( $sizes as $size => $size_data ) {
    $resized = bt_image_make_intermediate_size( $file, $size_data['width'], $size_data['height'], $size_data['crop'] );
    if ( $resized )
      $metadata['sizes'][$size] = $resized;
  }
  
  return $metadata;
}
 
 
/**
 * Resize an image to make a thumbnail or intermediate size.
 *
 * The returned array has the file size, the image width, and image height. The
 * filter 'image_make_intermediate_size' can be used to hook in and change the
 * values of the returned array. The only parameter is the resized file path.
 *
 * @param string $file File path.
 * @param int $width Image width.
 * @param int $height Image height.
 * @param bool|array $crop Optional, default is false. Whether to crop image to specified height and width or resize. An array can specify positioning of the crop area.
 * @return bool|array False, if no image was created. Metadata array on success.
 */
function bt_image_make_intermediate_size( $file, $width, $height, $crop = false ) {
  if ( $width || $height ) {
    $resized_file = bt_image_resize( $file, $width, $height, $crop, null, null, 90 );
    if ( !is_wp_error( $resized_file ) && $resized_file && $info = getimagesize( $resized_file ) ) {
      $resized_file = apply_filters('image_make_intermediate_size', $resized_file);
      return array(
        'file' => wp_basename( $resized_file ),
        'width' => $info[0],
        'height' => $info[1],
      );
    }
  }
  return false;
}
 
 
 
/**
 * Retrieve calculated resized dimensions for use in imagecopyresampled().
 *
 * Calculate dimensions and coordinates for a resized image that fits within a
 * specified width and height. If $crop is true, the largest matching central
 * portion of the image will be cropped out and resized to the required size.
 *
 * @param int $orig_w Original width.
 * @param int $orig_h Original height.
 * @param int $dest_w New width.
 * @param int $dest_h New height.
 * @param bool $crop Optional, default is false. Whether to crop image or resize.
 * @return bool|array False, on failure. Returned array matches parameters for imagecopyresampled() PHP function.
 */
function bt_image_resize_dimensions($orig_w, $orig_h, $dest_w, $dest_h, $crop = false) {
 
  if ($orig_w <= 0 || $orig_h <= 0)
    return false;
  // at least one of dest_w or dest_h must be specific
  if ($dest_w <= 0 && $dest_h <= 0)
    return false;
 
  if ( $crop ) {
    // crop the largest possible portion of the original image that we can size to $dest_w x $dest_h
    $aspect_ratio = $orig_w / $orig_h;
    $new_w = min($dest_w, $orig_w);
    $new_h = min($dest_h, $orig_h);
 
    if ( !$new_w ) {
      $new_w = intval($new_h * $aspect_ratio);
    }
 
    if ( !$new_h ) {
      $new_h = intval($new_w / $aspect_ratio);
    }
 
    $size_ratio = max($new_w / $orig_w, $new_h / $orig_h);
 
    $crop_w = round($new_w / $size_ratio);
    $crop_h = round($new_h / $size_ratio);
 
    if ( !is_array( $crop ) || count( $crop ) != 2 ) {
      $crop = apply_filters( 'image_resize_crop_default', array( 'center', 'center' ) );
    }
    
    switch ( $crop[0] ) {
      case 'left': $s_x = 0; break;
      case 'right': $s_x = $orig_w - $crop_w; break;
      default: $s_x = floor( ( $orig_w - $crop_w ) / 2 );
    }
 
    switch ( $crop[1] ) {
      case 'top': $s_y = 0; break;
      case 'bottom': $s_y = $orig_h - $crop_h; break;
      default: $s_y = floor( ( $orig_h - $crop_h ) / 2 );
    }
  } else {
    // don't crop, just resize using $dest_w x $dest_h as a maximum bounding box
    $crop_w = $orig_w;
    $crop_h = $orig_h;
 
    $s_x = 0;
    $s_y = 0;
 
    list( $new_w, $new_h ) = wp_constrain_dimensions( $orig_w, $orig_h, $dest_w, $dest_h );
  }
 
  // if the resulting image would be the same size or larger we don't want to resize it
  if ( $new_w >= $orig_w && $new_h >= $orig_h )
    return false;
 
  // the return array matches the parameters to imagecopyresampled()
  // int dst_x, int dst_y, int src_x, int src_y, int dst_w, int dst_h, int src_w, int src_h
  return array( 0, 0, (int) $s_x, (int) $s_y, (int) $new_w, (int) $new_h, (int) $crop_w, (int) $crop_h );
 
}
 
 
/**
 * Scale down an image to fit a particular size and save a new copy of the image.
 *
 * The PNG transparency will be preserved using the function, as well as the
 * image type. If the file going in is PNG, then the resized image is going to
 * be PNG. The only supported image types are PNG, GIF, and JPEG.
 *
 * Some functionality requires API to exist, so some PHP version may lose out
 * support. This is not the fault of WordPress (where functionality is
 * downgraded, not actual defects), but of your PHP version.
 *
 * @since 2.5.0
 *
 * @param string $file Image file path.
 * @param int $max_w Maximum width to resize to.
 * @param int $max_h Maximum height to resize to.
 * @param bool $crop Optional. Whether to crop image or resize.
 * @param string $suffix Optional. File Suffix.
 * @param string $dest_path Optional. New image file path.
 * @param int $jpeg_quality Optional, default is 90. Image quality percentage.
 * @return mixed WP_Error on failure. String with new destination path.
 */
function bt_image_resize( $file, $max_w, $max_h, $crop = false, $suffix = null, $dest_path = null, $jpeg_quality = 90 ) {
 
  $image = wp_load_image( $file );
  if ( !is_resource( $image ) )
    return new WP_Error( 'error_loading_image', $image, $file );
 
  $size = @getimagesize( $file );
  if ( !$size )
    return new WP_Error('invalid_image', __('Could not read image size'), $file);
  list($orig_w, $orig_h, $orig_type) = $size;
 
  // Rotate if EXIF 'Orientation' is set
  // This code is from the reverted patch at
  // <a href="http://core.trac.wordpress.org/changeset/11746/trunk/wp-includes/media.php">http://core.trac.wordpress.org/changeset/11746/trunk/wp-includes/media.php</a>
  $rotate = false;
  if ( is_callable( 'exif_read_data' ) && in_array( $orig_type, apply_filters( 'wp_read_image_metadata_types', array( IMAGETYPE_JPEG, IMAGETYPE_TIFF_II, IMAGETYPE_TIFF_MM ) ) ) ) {
    $exif = @exif_read_data( $file, null, true );
    if ( $exif && isset( $exif['IFD0'] ) && is_array( $exif['IFD0'] ) && isset( $exif['IFD0']['Orientation'] ) ) {
      if ( 6 == $exif['IFD0']['Orientation'] )
        $rotate = 90;
      elseif ( 8 == $exif['IFD0']['Orientation'] )
        $rotate = 270;
    }
  }
  
  if ( $rotate )
    list($max_h,$max_w) = array($max_w,$max_h);
 
  $dims = bt_image_resize_dimensions($orig_w, $orig_h, $max_w, $max_h, $crop);
  if ( !$dims )
    return new WP_Error( 'error_getting_dimensions', __('Could not calculate resized image dimensions') );
  list($dst_x, $dst_y, $src_x, $src_y, $dst_w, $dst_h, $src_w, $src_h) = $dims;
 
  $newimage = wp_imagecreatetruecolor( $dst_w, $dst_h );
 
  if ( $rotate )
    list($src_y,$src_x) = array($src_x,$src_y);
 
  imagecopyresampled( $newimage, $image, $dst_x, $dst_y, $src_x, $src_y, $dst_w, $dst_h, $src_w, $src_h);
 
  // convert from full colors to index colors, like original PNG.
  if ( IMAGETYPE_PNG == $orig_type && function_exists('imageistruecolor') && !imageistruecolor( $image ) )
    imagetruecolortopalette( $newimage, false, imagecolorstotal( $image ) );
 
  // we don't need the original in memory anymore
  imagedestroy( $image );
 
  // $suffix will be appended to the destination filename, just before the extension
  if ( !$suffix ) {
    if ( $rotate )
      $suffix = "{$dst_h}x{$dst_w}";
    else
      $suffix = "{$dst_w}x{$dst_h}";
  }
 
  $info = pathinfo($file);
  $dir = $info['dirname'];
  $ext = $info['extension'];
  $name = wp_basename($file, ".$ext");
 
  if ( !is_null($dest_path) and $_dest_path = realpath($dest_path) )
    $dir = $_dest_path;
  $destfilename = "{$dir}/{$name}-{$suffix}.{$ext}";
 
  if ( IMAGETYPE_GIF == $orig_type ) {
    if ( !imagegif( $newimage, $destfilename ) )
      return new WP_Error('resize_path_invalid', __( 'Resize path invalid' ));
  } elseif ( IMAGETYPE_PNG == $orig_type ) {
    if ( !imagepng( $newimage, $destfilename ) )
      return new WP_Error('resize_path_invalid', __( 'Resize path invalid' ));
  } else {
    if ( $rotate ) {
      $newimage = _rotate_image_resource( $newimage, 360 - $rotate );
    }
    
    // all other formats are converted to jpg
    $destfilename = "{$dir}/{$name}-{$suffix}.jpg";
    $return = imagejpeg( $newimage, $destfilename, apply_filters( 'jpeg_quality', $jpeg_quality, 'image_resize' ) );
    if ( !$return )
      return new WP_Error('resize_path_invalid', __( 'Resize path invalid' ));
  }
 
  imagedestroy( $newimage );
 
  // Set correct file permissions
  $stat = stat( dirname( $destfilename ));
  $perms = $stat['mode'] & 0000666; //same permissions as parent folder, strip off the executable bits
  @ chmod( $destfilename, $perms );
 
  return $destfilename;
}

这种方法需要你用bt_add_image_size代替原来我们习惯的add_image_size，具体的使用方法我们就不详细解释，总之这个函数给出了第三个参数，让你可以规定裁剪的开始位置。
而实际上，更为简洁的方法是，我找到一个插件，似乎可以实现这个功能，你不妨下载尝试。
Shailan.com Staff则提供了一个更直接的方法，就是修改wordpress系统文件/wp-includes/media.php，找到：

代码如下:

$s_x = floor( ($orig_w - $crop_w) / 2 );
$s_y = floor( ($orig_h - $crop_h) / 2 );

把其中的$s_y修改为：

代码如下:

$s_y = 0;// 或者你想要的值

总之，这种方法直接有效且最容易令人理解，因为$s_x和$s_y就是wordpress系统在裁剪时，裁剪区域的起始位置。而且他还推荐了一个插件：Regenerate Thumbnails，应是基于这种方法来实现的。
在stackexchange社区还有人用这样的方法更加便捷，或许你可以借鉴，但是否奏效还需要验证：

代码如下:

add_filter('wp_generate_attachment_metadata', 'custom_crop');</p>
<p>function custom_crop($metadata) {</p>
<p>  $uploads = wp_upload_dir();
  $file = path_join( $uploads['basedir'], $metadata['file'] ); // original image file
  list( $year, $month ) = explode( '/', $metadata['file'] );
  $target = path_join( $uploads['basedir'], "{$year}/{$month}/".$metadata['sizes']['medium']['file'] ); // intermediate size file
  $image = imagecreatefromjpeg($file); // original image resource
  $image_target = wp_imagecreatetruecolor( 44, 44 ); // blank image to fill
  imagecopyresampled($image_target, $image, 0, 0, 25, 15, 44, 44, 170, 170); // crop original
  imagejpeg($image_target, $target, apply_filters( 'jpeg_quality', 90, 'image_resize' )); // write cropped to file</p>
<p>  return $metadata;
}