allow registerFont after a canvas has been created

Fixes 1921

Author: chearon

CHANGELOG.md

@@ -10,6 +10,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 * Replaced `simple-get ` with ` Node.js builtin` `fetch` (#2309)
 * `ctx.font` has a new C++ parser and is 2x-400x faster. Please file an issue if you experience different results, as caching has been removed.
+* The restriction of registering fonts before a canvas is created has been removed. You can now register a font as late as right before the `fillText` call ([#1921](https://github.com/Automattic/node-canvas/issues/1921))
 
 ### Added
 * Support for accessibility and links in PDFs

src/Canvas.cc

@@ -38,7 +38,10 @@
 
 using namespace std;
 
-std::vector<FontFace> font_face_list;
+std::vector<FontFace> Canvas::font_face_list;
+
+// Increases each time a font is (de)registered
+int Canvas::fontSerial = 1;
 
 /*
  * Initialize Canvas.
@@ -734,6 +737,7 @@ Canvas::RegisterFont(const Napi::CallbackInfo& info) {
   free(family);
   free(weight);
   free(style);
+  fontSerial++;
 }
 
 void
@@ -749,6 +753,7 @@ Canvas::DeregisterAllFonts(const Napi::CallbackInfo& info) {
   });
 
   font_face_list.clear();
+  fontSerial++;
   if (!success) Napi::Error::New(env, "Could not deregister one or more fonts").ThrowAsJavaScriptException();
 }
 

src/Canvas.h

@@ -92,9 +92,11 @@ class Canvas : public Napi::ObjectWrap<Canvas> {
     void resurface(Napi::Object This);
 
     Napi::Env env;
+    static int fontSerial;
 
   private:
     Backend* _backend;
     Napi::ObjectReference _jsBackend;
     Napi::FunctionReference ctor;
+    static std::vector<FontFace> font_face_list;
 };

src/CanvasRenderingContext2d.cc

@@ -168,6 +168,18 @@ Context2d::Initialize(Napi::Env& env, Napi::Object& exports) {
   data->Context2dCtor = Napi::Persistent(ctor);
 }
 
+void
+Context2d::recreateLayout() {
+  if (_layout) g_object_unref(_layout);
+  _layout = pango_cairo_create_layout(_context);
+  // As of January 2023, Pango rounds glyph positions which renders text wider
+  // or narrower than the browser. See #2184 for more information
+#if PANGO_VERSION_CHECK(1, 44, 0)
+  pango_context_set_round_glyph_positions(pango_layout_get_context(_layout), FALSE);
+#endif
+  pango_layout_set_font_description(_layout, state->fontDescription);
+}
+
 /*
  * Create a cairo context.
  */
@@ -222,17 +234,10 @@ Context2d::Context2d(const Napi::CallbackInfo& info) : Napi::ObjectWrap<Context2
   }
 
   _context = _canvas->createCairoContext();
-  _layout = pango_cairo_create_layout(_context);
-
-  // As of January 2023, Pango rounds glyph positions which renders text wider
-  // or narrower than the browser. See #2184 for more information
-#if PANGO_VERSION_CHECK(1, 44, 0)
-  pango_context_set_round_glyph_positions(pango_layout_get_context(_layout), FALSE);
-#endif
 
   states.emplace();
   state = &states.top();
-  pango_layout_set_font_description(_layout, state->fontDescription);
+  recreateLayout();
 }
 
 /*
@@ -2446,6 +2451,12 @@ Context2d::paintText(const Napi::CallbackInfo&info, bool stroke) {
   double y = args[1];
   double scaled_by = 1;
 
+  // If fonts have been registered, the PangoLayout is using an outdated FontMap
+  if (canvas()->fontSerial != fontSerial) {
+    recreateLayout();
+    fontSerial = canvas()->fontSerial;
+  }
+
   PangoLayout *layout = this->layout();
 
   pango_layout_set_text(layout, str.c_str(), -1);

src/CanvasRenderingContext2d.h

@@ -205,6 +205,7 @@ class Context2d : public Napi::ObjectWrap<Context2d> {
     void setFontFromState();
     void resetState();
     inline PangoLayout *layout(){ return _layout; }
+    void recreateLayout();
     ~Context2d();
     Napi::Env env;
 
@@ -224,4 +225,5 @@ class Context2d : public Napi::ObjectWrap<Context2d> {
     cairo_t *_context = nullptr;
     cairo_path_t *_path;
     PangoLayout *_layout = nullptr;
+    int fontSerial = 0;
 };