Prevent transparency loss in AVIF by falling back to WebP on older ImageMagick

plugins/webp-uploads/helper.php

@@ -374,6 +374,11 @@ function webp_uploads_mime_type_supported( string $mime_type ): bool {
  * @return string The image output format. One of 'webp' or 'avif'.
  */
 function webp_uploads_get_image_output_format(): string {
+	if ( ! webp_uploads_imagick_avif_transparency_supported() && (bool) wp_cache_get( 'webp_uploads_image_has_transparency', 'webp-uploads' ) ) {
+		wp_cache_delete( 'webp_uploads_image_has_transparency', 'webp-uploads' );
+		return 'webp';
+	}
+
 	$image_format = get_option( 'perflab_modern_image_format' );
 	return webp_uploads_sanitize_image_format( $image_format );
 }
@@ -512,3 +517,24 @@ function webp_uploads_get_attachment_file_mime_type( int $attachment_id, string
 	$mime_type = $filetype['type'] ?? get_post_mime_type( $attachment_id );
 	return is_string( $mime_type ) ? $mime_type : '';
 }
+
+/**
+ * Checks if Imagick has AVIF transparency support.
+ *
+ * @since n.e.x.t
+ *
+ * @return bool True if Imagick has AVIF transparency support, false otherwise.
+ */
+function webp_uploads_imagick_avif_transparency_supported(): bool {
+	if ( extension_loaded( 'imagick' ) && class_exists( 'Imagick' ) ) {
+		$imagick_version = Imagick::getVersion();
+		if ( (bool) preg_match( '/((?:[0-9]+\\.?)+)/', $imagick_version['versionString'], $matches ) ) {
+			$imagick_version = $matches[0];
+		} else {
+			$imagick_version = $imagick_version['versionString'];
+		}
+		return version_compare( $imagick_version, '7.0.25', '>=' );
+	}
+
+	return false;
+}

plugins/webp-uploads/hooks.php

@@ -966,3 +966,53 @@ function webp_uploads_convert_palette_png_to_truecolor( $file ): array {
 }
 add_filter( 'wp_handle_upload_prefilter', 'webp_uploads_convert_palette_png_to_truecolor' );
 add_filter( 'wp_handle_sideload_prefilter', 'webp_uploads_convert_palette_png_to_truecolor' );
+
+/**
+ * Checks if an image has transparency when uploading AVIF images with Imagick.
+ *
+ * @since n.e.x.t
+ *
+ * @param array<string, mixed>|mixed $file The uploaded file data.
+ * @return array<string, mixed> The modified file data.
+ */
+function webp_uploads_check_image_transparency( $file ): array {
+	if ( 'avif' !== webp_uploads_get_image_output_format() || webp_uploads_imagick_avif_transparency_supported() ) {
+		return $file;
+	}
+
+	// Because plugins do bad things.
+	if ( ! is_array( $file ) ) {
+		$file = array();
+	}
+	if ( ! isset( $file['tmp_name'], $file['name'] ) ) {
+		return $file;
+	}
+	if ( isset( $file['type'] ) && is_string( $file['type'] ) ) {
+		if ( ! str_starts_with( strtolower( $file['type'] ), 'image/' ) ) {
+			return $file;
+		}
+	} elseif ( ! str_starts_with( strtolower( (string) wp_check_filetype_and_ext( $file['tmp_name'], $file['name'] )['type'] ), 'image/' ) ) {
+		return $file;
+	}
+
+	$editor = wp_get_image_editor( $file['tmp_name'] );
+
+	if ( is_wp_error( $editor ) || ! $editor instanceof WP_Image_Editor_Imagick ) {
+		return $file;
+	}
+
+	$reflection     = new ReflectionClass( $editor );
+	$image_property = $reflection->getProperty( 'image' );
+	if ( PHP_VERSION_ID < 80100 ) {
+		$image_property->setAccessible( true );
+	}
+	$imagick = $image_property->getValue( $editor );
+
+	if ( $imagick instanceof Imagick ) {
+		wp_cache_set( 'webp_uploads_image_has_transparency', (bool) $imagick->getImageAlphaChannel(), 'webp-uploads' );
+	}
+
+	return $file;
+}
+add_filter( 'wp_handle_upload_prefilter', 'webp_uploads_check_image_transparency' );
+add_filter( 'wp_handle_sideload_prefilter', 'webp_uploads_check_image_transparency' );