From a43793ee0df37519d63562552abaed754a495649 Mon Sep 17 00:00:00 2001
From: Lucas CHOLLET <lucas.chollet@free.fr>
Date: Sat, 3 Feb 2024 16:34:31 -0500
Subject: [PATCH] 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.
---
 .../Libraries/LibGfx/ImageFormats/TIFFLoader.cpp     | 11 +++++++++--
 Userland/Libraries/LibGfx/TIFFGenerator.py           | 12 ++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.cpp b/Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.cpp
index 5b47182dca5f26..9eecea584e9aac 100644
--- a/Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.cpp
+++ b/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 {};
     }
diff --git a/Userland/Libraries/LibGfx/TIFFGenerator.py b/Userland/Libraries/LibGfx/TIFFGenerator.py
index 32766f25403ef6..eaacdb5672fa41 100755
--- a/Userland/Libraries/LibGfx/TIFFGenerator.py
+++ b/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::")
 
@@ -478,6 +479,12 @@ 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}
 
@@ -485,6 +492,7 @@ def generate_tag_handler(tag: Tag) -> str:
 
         {pre_condition}
         {check_value}
+        {handle_subifd}
         metadata.add_entry("{tag.name}"sv, move(value));
         break;
 """