allow user to cancel decoding process (#546)

go/heif/heif.go

@@ -179,6 +179,8 @@ const (
 	ErrorColorProfileDoesNotExist = C.heif_error_Color_profile_does_not_exist
 
 	ErrorPluginLoadingError = C.heif_error_Plugin_loading_error
+
+	ErrorCanceled = C.heif_error_Canceled
 )
 
 type ErrorSubcode C.enum_heif_suberror_code

libheif/api/libheif/heif.cc

@@ -1272,7 +1272,7 @@ struct heif_error heif_image_handle_get_depth_image_handle(const struct heif_ima
 
 void fill_default_decoding_options(heif_decoding_options& options)
 {
-  options.version = 5;
+  options.version = 6;
 
   options.ignore_transformations = false;
 
@@ -1299,6 +1299,10 @@ void fill_default_decoding_options(heif_decoding_options& options)
   options.color_conversion_options.preferred_chroma_downsampling_algorithm = heif_chroma_downsampling_average;
   options.color_conversion_options.preferred_chroma_upsampling_algorithm = heif_chroma_upsampling_bilinear;
   options.color_conversion_options.only_use_preferred_chroma_algorithm = false;
+
+  // version 6
+
+  options.cancel_decoding = nullptr;
 }
 
 
@@ -1310,6 +1314,9 @@ static heif_decoding_options normalize_options(const heif_decoding_options* inpu
 
   if (input_options) {
     switch (input_options->version) {
+      case 6:
+        options.cancel_decoding = input_options->cancel_decoding;
+        // fallthrough
       case 5:
         options.color_conversion_options = input_options->color_conversion_options;
         // fallthrough

libheif/api/libheif/heif.h

@@ -53,7 +53,7 @@ extern "C" {
 //  1.15           4            5             1             1            1            1
 //  1.16           5            6             1             1            1            1
 //  1.18           5            7             1             1            1            1
-//  1.19           5            7             2             1            1            1
+//  1.19           6            7             2             1            1            1
 
 #if defined(_MSC_VER) && !defined(LIBHEIF_STATIC_BUILD)
 #ifdef LIBHEIF_EXPORTS
@@ -135,7 +135,10 @@ enum heif_error_code
   heif_error_Color_profile_does_not_exist = 10,
 
   // Error loading a dynamic plugin
-  heif_error_Plugin_loading_error = 11
+  heif_error_Plugin_loading_error = 11,
+
+  // Operation has been canceled
+  heif_error_Canceled = 12
 };
 
 
@@ -1740,10 +1743,13 @@ struct heif_decoding_options
   // The priority is defined in the plugin.
   const char* decoder_id;
 
-
   // version 5 options
 
   struct heif_color_conversion_options color_conversion_options;
+
+  // version 6 options
+
+  int (* cancel_decoding)(void* progress_user_data);
 };
 
 

libheif/api/libheif/heif_emscripten.h

@@ -327,7 +327,8 @@ EMSCRIPTEN_BINDINGS(libheif) {
     .value("heif_error_Decoder_plugin_error", heif_error_Decoder_plugin_error)
     .value("heif_error_Encoder_plugin_error", heif_error_Encoder_plugin_error)
     .value("heif_error_Encoding_error", heif_error_Encoding_error)
-    .value("heif_error_Color_profile_does_not_exist", heif_error_Color_profile_does_not_exist);
+    .value("heif_error_Color_profile_does_not_exist", heif_error_Color_profile_does_not_exist)
+    .value("heif_error_Canceled", heif_error_Canceled);
     emscripten::enum_<heif_suberror_code>("heif_suberror_code")
     .value("heif_suberror_Unspecified", heif_suberror_Unspecified)
     .value("heif_suberror_Cannot_write_output_data", heif_suberror_Cannot_write_output_data)

libheif/error.cc

@@ -70,6 +70,8 @@ const char* Error::get_error_string(heif_error_code err)
       return "Color profile does not exist";
     case heif_error_Plugin_loading_error:
       return "Error while loading plugin";
+    case heif_error_Canceled:
+      return "Canceled by user";
   }
 
   assert(false);

libheif/image-items/grid.cc

@@ -282,11 +282,12 @@ Result<std::shared_ptr<HeifPixelImage>> ImageItem_Grid::decode_full_grid_image(c
   }
 
   int progress_counter = 0;
+  bool cancelled = false;
 
-  for (uint32_t y = 0; y < grid.get_rows(); y++) {
+  for (uint32_t y = 0; y < grid.get_rows() && !cancelled; y++) {
     uint32_t x0 = 0;
 
-    for (uint32_t x = 0; x < grid.get_columns(); x++) {
+    for (uint32_t x = 0; x < grid.get_columns() && !cancelled; x++) {
 
       heif_item_id tileID = image_references[reference_idx];
 
@@ -333,6 +334,12 @@ Result<std::shared_ptr<HeifPixelImage>> ImageItem_Grid::decode_full_grid_image(c
         if (1)
 #endif
       {
+        if (options.cancel_decoding) {
+          if (options.cancel_decoding(options.progress_user_data)) {
+            cancelled = true;
+          }
+        }
+
         err = decode_and_paste_tile_image(tileID, x0, y0, img, options, progress_counter);
         if (err) {
           return err;
@@ -352,7 +359,7 @@ Result<std::shared_ptr<HeifPixelImage>> ImageItem_Grid::decode_full_grid_image(c
     // Process all tiles in a set of background threads.
     // Do not start more than the maximum number of threads.
 
-    while (!tiles.empty()) {
+    while (!tiles.empty() && !cancelled) {
 
       // If maximum number of threads running, wait until first thread finishes
 
@@ -366,6 +373,13 @@ Result<std::shared_ptr<HeifPixelImage>> ImageItem_Grid::decode_full_grid_image(c
       }
 
 
+      if (options.cancel_decoding) {
+        if (options.cancel_decoding(options.progress_user_data)) {
+          cancelled = true;
+        }
+      }
+
+
       // Start a new decoding thread
 
       tile_data data = tiles.front();
@@ -394,6 +408,10 @@ Result<std::shared_ptr<HeifPixelImage>> ImageItem_Grid::decode_full_grid_image(c
     options.end_progress(heif_progress_step_total, options.progress_user_data);
   }
 
+  if (cancelled) {
+    return Error{heif_error_Canceled, heif_suberror_Unspecified, "Decoding the image was canceled"};
+  }
+
   return img;
 }