LibGfx/TIFF: Explore underlying Image File Directories

Every TIFF containers is composed of a main IFD. Some entries of this
one can be a pointer to a sub-IFD. We are now capable of exploring these
underlying structures. Note that we don't do anything with them yet.

Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.cpp

@@ -453,7 +453,6 @@ class TIFFLoadingContext {
  m_next_ifd = Optional<u32> { next_block_position };
  else
  m_next_ifd = OptionalNone {};
- dbgln_if(TIFF_DEBUG, "Setting image file directory pointer to {}", m_next_ifd);
  return {};
  }
 
@@ -491,6 +490,8 @@ class TIFFLoadingContext {
  if (!m_next_ifd.has_value())
  return Error::from_string_literal("TIFFImageDecoderPlugin: Missing an Image File Directory");
 
+ dbgln_if(TIFF_DEBUG, "Reading image file directory at offset {}", m_next_ifd);
+
  TRY(m_stream->seek(m_next_ifd.value()));
 
  auto const number_of_field = TRY(read_value<u16>());
@@ -597,7 +598,13 @@ class TIFFLoadingContext {
  return read_tiff_value(type, count, offset);
  }()));
 
- TRY(handle_tag(m_metadata, tag, type, count, move(tiff_value)));
+ auto subifd_handler = [&](u32 ifd_offset) -> ErrorOr<void> {
+ m_next_ifd = ifd_offset;
+ TRY(read_next_image_file_directory());
+ return {};
+ };
+
+ TRY(handle_tag(move(subifd_handler), m_metadata, tag, type, count, move(tiff_value)));
 
  return {};
  }

Userland/Libraries/LibGfx/TIFFGenerator.py

@@ -148,8 +148,9 @@ class ExtraSample(EnumWithExportName):
  Tag('34675', [TIFFType.Undefined], [], None, "ICCProfile"),
 ]
 
-HANDLE_TAG_SIGNATURE_TEMPLATE = ("ErrorOr<void> {namespace}handle_tag(ExifMetadata& metadata, u16 tag,"
- " {namespace}Type type, u32 count, Vector<{namespace}Value>&& value)")
+HANDLE_TAG_SIGNATURE_TEMPLATE = ("ErrorOr<void> {namespace}handle_tag(Function<ErrorOr<void>(u32)>&& subifd_handler, "
+ "ExifMetadata& metadata, u16 tag, {namespace}Type type, u32 count, "
+ "Vector<{namespace}Value>&& value)")
 HANDLE_TAG_SIGNATURE = HANDLE_TAG_SIGNATURE_TEMPLATE.format(namespace="")
 HANDLE_TAG_SIGNATURE_TIFF_NAMESPACE = HANDLE_TAG_SIGNATURE_TEMPLATE.format(namespace="TIFF::")
 
@@ -478,13 +479,20 @@ def generate_tag_handler(tag: Tag) -> str:
  }}
 """
 
+ handle_subifd = ''
+ if TIFFType.IFD in tag.types:
+ if tag.counts != [1]:
+ raise RuntimeError("Accessing `value[0]` in the C++ code might fail!")
+ handle_subifd = f'TRY(subifd_handler(value[0].get<{tiff_type_to_cpp(TIFFType.IFD)}>()));'
+
  output = fR""" case {tag.id}:
  // {tag.name}
 
  dbgln_if(TIFF_DEBUG, "{tag.name}({{}}): {{}}", name_for_enum_tag_value(type), format_tiff_value(tag, value));
 
  {pre_condition}
  {check_value}
+ {handle_subifd}
  metadata.add_entry("{tag.name}"sv, move(value));
  break;
 """