LibPDF: Sketch out Type0 font support some more

Type0 fonts can be either CFF-based or TrueType-based.
Create a subclass for each, put in some spec text, and
give each case a dedicated error code, so that `--debugging-stats`
can tell me which branch is more common.

Userland/Libraries/LibPDF/CommonNames.h

@@ -27,6 +27,8 @@
     A(CF)                         \
     A(CFM)                        \
     A(CalRGB)                     \
+    A(CIDFontType0)               \
+    A(CIDFontType2)               \
     A(CIDSystemInfo)              \
     A(CIDToGIDMap)                \
     A(Colors)                     \

Userland/Libraries/LibPDF/Fonts/Type0Font.cpp

@@ -9,6 +9,57 @@
 
 namespace PDF {
 
+class CIDFontType {
+public:
+    virtual ~CIDFontType() = default;
+    virtual PDFErrorOr<Gfx::FloatPoint> draw_string(Gfx::Painter&, Gfx::FloatPoint, DeprecatedString const&, Color const&, float, float, float, float) = 0;
+};
+
+class CIDFontType0 : public CIDFontType {
+public:
+    PDFErrorOr<Gfx::FloatPoint> draw_string(Gfx::Painter&, Gfx::FloatPoint, DeprecatedString const&, Color const&, float, float, float, float) override;
+};
+
+PDFErrorOr<Gfx::FloatPoint> CIDFontType0::draw_string(Gfx::Painter&, Gfx::FloatPoint, DeprecatedString const&, Color const&, float, float, float, float)
+{
+    // ISO 32000 (PDF 2.0) 9.7.4.2 Glyph selection in CIDFonts
+    // "When the CIDFont contains an embedded font program that is represented in the Compact Font Format (CFF),
+    //  the FontFile3 entry in the font descriptor (...) shall be either CIDFontType0C or OpenType.
+    //  There are two cases, depending on the contents of the font program:
+    //  * The "CFF" font program has a Top DICT that uses CIDFont operators: The CIDs shall be used to determine
+    //    the GID value for the glyph procedure using the charset table in the CFF program.
+    //    The GID value shall then be used to look up the glyph procedure using the CharStrings INDEX table [...]
+    //  * The "CFF" font program has a Top DICT that does not use CIDFont operators: The CIDs shall be used
+    //    directly as GID values, and the glyph procedure shall be retrieved using the CharStrings INDEX"
+    return Error::rendering_unsupported_error("Type0 font CIDFontType0 not implemented yet");
+}
+
+class CIDFontType2 : public CIDFontType {
+public:
+    PDFErrorOr<Gfx::FloatPoint> draw_string(Gfx::Painter&, Gfx::FloatPoint, DeprecatedString const&, Color const&, float, float, float, float) override;
+};
+
+PDFErrorOr<Gfx::FloatPoint> CIDFontType2::draw_string(Gfx::Painter&, Gfx::FloatPoint, DeprecatedString const&, Color const&, float, float, float, float)
+{
+    // ISO 32000 (PDF 2.0) 9.7.4.2 Glyph selection in CIDFonts
+    // "For Type 2, the CIDFont program is actually a TrueType font program, which has no native notion of CIDs.
+    //  In a TrueType font program, glyph descriptions are identified by glyph index values.
+    //  Glyph indices are internal to the font and are not defined consistently from one font to another.
+    //  Instead, a TrueType font program contains a "cmap" table that provides mappings directly from
+    //  character codes to glyph indices for one or more predefined encodings.
+    //  TrueType font programs are integrated with the CID-keyed font architecture in one of two ways,
+    //  depending on whether the font program is embedded in the PDF file:
+    //  * If the TrueType font program is embedded, the Type 2 CIDFont dictionary shall contain a CIDToGIDMap entry
+    //    that maps CIDs to the glyph indices for the appropriate glyph descriptions in that font program.
+    //  * If the TrueType font program is not embedded but is referenced by name, and the Type 2 CIDFont dictionary
+    //    contains a CIDToGIDMap entry, the CIDToGIDMap entry shall be ignored, since it is not meaningful
+    ///   to refer to glyph indices in an external font program."
+    return Error::rendering_unsupported_error("Type0 font CIDFontType2 not implemented yet");
+}
+
+Type0Font::Type0Font() = default;
+Type0Font::~Type0Font() = default;
+
 PDFErrorOr<void> Type0Font::initialize(Document* document, NonnullRefPtr<DictObject> const& dict, float font_size)
 {
     TRY(PDFFont::initialize(document, dict, font_size));
@@ -27,6 +78,17 @@ PDFErrorOr<void> Type0Font::initialize(Document* document, NonnullRefPtr<DictObj
     u8 supplement = system_info_dict->get_value(CommonNames::Supplement).get<int>();
     CIDSystemInfo system_info { registry, ordering, supplement };
 
+    auto subtype = TRY(descendant_font->get_name(document, CommonNames::Subtype))->name();
+    if (subtype == CommonNames::CIDFontType0) {
+        // CFF-based
+        m_cid_font_type = TRY(try_make<CIDFontType0>());
+    } else if (subtype == CommonNames::CIDFontType2) {
+        // TrueType-based
+        m_cid_font_type = TRY(try_make<CIDFontType2>());
+    } else {
+        return Error { Error::Type::MalformedPDF, "invalid /Subtype for Type 0 font" };
+    }
+
     auto font_descriptor = TRY(descendant_font->get_dict(document, CommonNames::FontDescriptor));
 
     u16 default_width = 1000;
@@ -91,9 +153,9 @@ void Type0Font::set_font_size(float)
 {
 }
 
-PDFErrorOr<Gfx::FloatPoint> Type0Font::draw_string(Gfx::Painter&, Gfx::FloatPoint, DeprecatedString const&, Color const&, float, float, float, float)
+PDFErrorOr<Gfx::FloatPoint> Type0Font::draw_string(Gfx::Painter& painter, Gfx::FloatPoint glyph_position, DeprecatedString const& string, Color const& paint_color, float font_size, float character_spacing, float word_spacing, float horizontal_scaling)
 {
-    return Error::rendering_unsupported_error("Type0 font not implemented yet");
+    return m_cid_font_type->draw_string(painter, glyph_position, string, paint_color, font_size, character_spacing, word_spacing, horizontal_scaling);
 }
 
 }

Userland/Libraries/LibPDF/Fonts/Type0Font.h

@@ -6,11 +6,14 @@
 
 #pragma once
 
+#include <AK/OwnPtr.h>
 #include <LibGfx/Point.h>
 #include <LibPDF/Fonts/PDFFont.h>
 
 namespace PDF {
 
+class CIDFontType;
+
 struct CIDSystemInfo {
     DeprecatedString registry;
     DeprecatedString ordering;
@@ -19,6 +22,9 @@ struct CIDSystemInfo {
 
 class Type0Font : public PDFFont {
 public:
+    Type0Font();
+    ~Type0Font();
+
     void set_font_size(float font_size) override;
     PDFErrorOr<Gfx::FloatPoint> draw_string(Gfx::Painter&, Gfx::FloatPoint pos, DeprecatedString const&, Color const&, float, float, float, float) override;
     Type type() const override { return PDFFont::Type::Type0; }
@@ -32,6 +38,7 @@ private:
     CIDSystemInfo m_system_info;
     HashMap<u16, u16> m_widths;
     u16 m_missing_width;
+    OwnPtr<CIDFontType> m_cid_font_type;
 };
 
 }