implement Box_ster (stereo entity group)

libheif/box.cc

@@ -548,10 +548,13 @@ Error Box::read(BitstreamRange& range, std::shared_ptr<Box>* result)
       break;
 
     case fourcc("altr"):
-    case fourcc("ster"):
       box = std::make_shared<Box_EntityToGroup>();
       break;
 
+    case fourcc("ster"):
+      box = std::make_shared<Box_ster>();
+      break;
+
     case fourcc("dinf"):
       box = std::make_shared<Box_dinf>();
       break;
@@ -3259,6 +3262,36 @@ std::string Box_EntityToGroup::dump(Indent& indent) const
 }
 
 
+Error Box_ster::parse(BitstreamRange& range)
+{
+  Error err = Box_EntityToGroup::parse(range);
+  if (err) {
+    return err;
+  }
+
+  if (entity_ids.size() != 2) {
+    return {heif_error_Invalid_input,
+            heif_suberror_Invalid_box_size,
+            "'ster' entity group does not exists of exactly two images"};
+  }
+
+  return Error::Ok;
+}
+
+
+std::string Box_ster::dump(Indent& indent) const
+{
+  std::ostringstream sstr;
+  sstr << Box::dump(indent);
+
+  sstr << indent << "group id: " << group_id << "\n"
+       << indent << "left image ID " << entity_ids[0] << "\n"
+       << indent << "right image ID " << entity_ids[1] << "\n";
+
+  return sstr.str();
+}
+
+
 
 Error Box_pymd::parse(BitstreamRange& range)
 {

libheif/box.h

@@ -884,6 +884,20 @@ class Box_EntityToGroup : public FullBox
 };
 
 
+class Box_ster : public Box_EntityToGroup
+{
+public:
+  std::string dump(Indent&) const override;
+
+  heif_item_id get_left_image() const { return entity_ids[0]; }
+  heif_item_id get_right_image() const { return entity_ids[1]; }
+
+protected:
+
+  Error parse(BitstreamRange& range) override;
+};
+
+
 class Box_pymd : public Box_EntityToGroup
 {
 public: