LibPDF: Use font dictionary object as cache key, not resource name

In the main page contents, /T0 might refer to a different font than
it might refer to in an XObject. So don't use the `Tf` argument as
font cache key. Instead, use the address of the font dictionary object.

Fixes false cache sharing, and also allows us to share cache entries
if the same font dict is referred to by two different names.

Fixes a regression from 2340e834cd (but keeps the speed-up intact).

Userland/Libraries/LibPDF/Renderer.cpp

@@ -406,17 +406,13 @@ RENDERER_HANDLER(text_set_leading)
     return {};
 }
 
-PDFErrorOr<NonnullRefPtr<PDFFont>> Renderer::get_font(FontCacheKey const& key, Optional<NonnullRefPtr<DictObject>> extra_resources)
+PDFErrorOr<NonnullRefPtr<PDFFont>> Renderer::get_font(FontCacheKey const& key)
 {
     auto it = m_font_cache.find(key);
     if (it != m_font_cache.end())
         return it->value;
 
-    auto resources = extra_resources.value_or(m_page.resources);
-    auto fonts_dictionary = MUST(resources->get_dict(m_document, CommonNames::Font));
-    auto font_dictionary = MUST(fonts_dictionary->get_dict(m_document, key.font_dictionary_key));
-
-    auto font = TRY(PDFFont::create(m_document, font_dictionary, key.font_size));
+    auto font = TRY(PDFFont::create(m_document, key.font_dictionary, key.font_size));
     m_font_cache.set(key, font);
     return font;
 }
@@ -430,8 +426,12 @@ RENDERER_HANDLER(text_set_font)
     auto& text_rendering_matrix = calculate_text_rendering_matrix();
     auto font_size = text_rendering_matrix.x_scale() * text_state().font_size;
 
-    FontCacheKey cache_key { target_font_name, font_size };
-    text_state().font = TRY(get_font(cache_key, extra_resources));
+    auto resources = extra_resources.value_or(m_page.resources);
+    auto fonts_dictionary = MUST(resources->get_dict(m_document, CommonNames::Font));
+    auto font_dictionary = MUST(fonts_dictionary->get_dict(m_document, target_font_name));
+
+    FontCacheKey cache_key { move(font_dictionary), font_size };
+    text_state().font = TRY(get_font(cache_key));
 
     m_text_rendering_matrix_is_dirty = true;
     return {};

Userland/Libraries/LibPDF/Renderer.h

@@ -101,7 +101,7 @@ public:
     static PDFErrorsOr<void> render(Document&, Page const&, RefPtr<Gfx::Bitmap>, RenderingPreferences preferences);
 
     struct FontCacheKey {
-        DeprecatedString font_dictionary_key;
+        NonnullRefPtr<DictObject> font_dictionary;
         float font_size;
 
         bool operator==(FontCacheKey const&) const = default;
@@ -147,7 +147,7 @@ private:
     Gfx::AffineTransform const& calculate_text_rendering_matrix();
     Gfx::AffineTransform calculate_image_space_transformation(int width, int height);
 
-    PDFErrorOr<NonnullRefPtr<PDFFont>> get_font(FontCacheKey const&, Optional<NonnullRefPtr<DictObject>> extra_resources);
+    PDFErrorOr<NonnullRefPtr<PDFFont>> get_font(FontCacheKey const&);
 
     RefPtr<Document> m_document;
     RefPtr<Gfx::Bitmap> m_bitmap;
@@ -175,7 +175,7 @@ template<>
 struct Traits<PDF::Renderer::FontCacheKey> : public DefaultTraits<PDF::Renderer::FontCacheKey> {
     static unsigned hash(PDF::Renderer::FontCacheKey const& key)
     {
-        return pair_int_hash(key.font_dictionary_key.hash(), int_hash(bit_cast<u32>(key.font_size)));
+        return pair_int_hash(ptr_hash(key.font_dictionary.ptr()), int_hash(bit_cast<u32>(key.font_size)));
     }
 };