LibPDF: Add missing character quirk for WinAnsiEncoding fonts

Fonts with the encoding name "WinAnsiEncoding" should render missing
characters above character code 040 (octal) as a "bullet" character.

This patch adds Encoding::should_map_to_bullet(char_code) which is then
called by char_code_to_code_point() to check if the given char code
should be displayed as a bullet instead.

I didn't have a good way to test this, so I've only verified that it
works by manually overriding inputs to the function during the rendering
stage.

This takes care of a FIXME in the Annex D part of the PDF specification.

1 files changed, 9 insertions, 0 deletions

diff --git a/Userland/Libraries/LibPDF/Encoding.cpp b/Userland/Libraries/LibPDF/Encoding.cpp
index e8cd5c7ba0..f18152dafe 100644
--- a/Userland/Libraries/LibPDF/Encoding.cpp
+++ b/Userland/Libraries/LibPDF/Encoding.cpp
@@ -115,6 +115,7 @@ NonnullRefPtr<Encoding> Encoding::windows_encoding()
     encoding->m_name_mapping.set(#name, name##_code_point);
         ENUMERATE_LATIN_CHARACTER_SET(ENUMERATE)
 #undef ENUMERATE
+        encoding->m_windows = true;
     }
 
     return encoding;
@@ -170,4 +171,12 @@ CharDescriptor const& Encoding::get_char_code_descriptor(u16 char_code) const
     return const_cast<Encoding*>(this)->m_descriptors.ensure(char_code);
 }
 
+bool Encoding::should_map_to_bullet(u16 char_code) const
+{
+    // PDF Annex D table D.2, note 3:
+    // In WinAnsiEncoding, all unused codes greater than 40 (octal) map to the bullet character. However, only
+    // code 225 (octal) shall be specifically assigned to the bullet character; other codes are subject to future re-assignment.
+    return m_windows && char_code > 040 && !m_descriptors.contains(char_code);
+}
+
 }