(Conditionally) add further dithering algorithms

lib/Epub/Epub/converters/ImageToFramebufferDecoder.h

@@ -13,12 +13,15 @@ struct ImageDimensions {
 
 enum class ImageDitherMode : uint8_t {
   Bayer = 0,
+#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
   Atkinson = 1,
   DiffusedBayer = 2,
+#endif
   COUNT,
 };
 
 inline ImageDitherMode imageDitherModeFromSetting(uint8_t value) {
+#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
   switch (static_cast<ImageDitherMode>(value)) {
     case ImageDitherMode::Bayer:
     case ImageDitherMode::Atkinson:
@@ -28,14 +31,20 @@ inline ImageDitherMode imageDitherModeFromSetting(uint8_t value) {
     default:
       return ImageDitherMode::Bayer;
   }
+#else
+  (void)value;
+  return ImageDitherMode::Bayer;
+#endif
 }
 
 inline const char* getImageDitherCacheSuffix(ImageDitherMode mode) {
   switch (mode) {
+#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
     case ImageDitherMode::Atkinson:
       return ".atkinson";
     case ImageDitherMode::DiffusedBayer:
       return ".diffused-bayer";
+#endif
     case ImageDitherMode::Bayer:
     case ImageDitherMode::COUNT:
     default: