[Impeller] dont append to existing atlas if type changed (#39913)

[Impeller] dont append to existing atlas if type changed

Author: Jonah Williams

impeller/typographer/backends/skia/text_render_context_skia.cc

@@ -473,10 +473,12 @@ std::shared_ptr<GlyphAtlas> TextRenderContextSkia::CreateGlyphAtlas(
 
   // ---------------------------------------------------------------------------
   // Step 3: Determine if the additional missing glyphs can be appended to the
-  //         existing bitmap without recreating the atlas.
+  //         existing bitmap without recreating the atlas. This requires that
+  //         the type is identical.
   // ---------------------------------------------------------------------------
   std::vector<Rect> glyph_positions;
-  if (CanAppendToExistingAtlas(last_atlas, new_glyphs, glyph_positions,
+  if (last_atlas->GetType() == type &&
+      CanAppendToExistingAtlas(last_atlas, new_glyphs, glyph_positions,
                                atlas_context->GetAtlasSize(),
                                atlas_context->GetRectPacker())) {
     // The old bitmap will be reused and only the additional glyphs will be

impeller/typographer/typographer_unittests.cc

@@ -201,6 +201,40 @@ TEST_P(TypographerTest, GlyphAtlasTextureIsRecycledIfUnchanged) {
   ASSERT_EQ(old_packer, new_packer);
 }
 
+TEST_P(TypographerTest, GlyphAtlasTextureIsRecreatedIfTypeChanges) {
+  auto context = TextRenderContext::Create(GetContext());
+  auto atlas_context = std::make_shared<GlyphAtlasContext>();
+  ASSERT_TRUE(context && context->IsValid());
+  SkFont sk_font;
+  auto blob = SkTextBlob::MakeFromString("spooky 1", sk_font);
+  ASSERT_TRUE(blob);
+  auto atlas =
+      context->CreateGlyphAtlas(GlyphAtlas::Type::kAlphaBitmap, atlas_context,
+                                TextFrameFromTextBlob(blob));
+  auto old_packer = atlas_context->GetRectPacker();
+
+  ASSERT_NE(atlas, nullptr);
+  ASSERT_NE(atlas->GetTexture(), nullptr);
+  ASSERT_EQ(atlas, atlas_context->GetGlyphAtlas());
+
+  auto* first_texture = atlas->GetTexture().get();
+
+  // now create a new glyph atlas with an identical blob,
+  // but change the type.
+
+  auto blob2 = SkTextBlob::MakeFromString("spooky 1", sk_font);
+  auto next_atlas =
+      context->CreateGlyphAtlas(GlyphAtlas::Type::kColorBitmap, atlas_context,
+                                TextFrameFromTextBlob(blob2));
+  ASSERT_NE(atlas, next_atlas);
+  auto* second_texture = next_atlas->GetTexture().get();
+
+  auto new_packer = atlas_context->GetRectPacker();
+
+  ASSERT_NE(second_texture, first_texture);
+  ASSERT_NE(old_packer, new_packer);
+}
+
 TEST_P(TypographerTest, FontGlyphPairTypeChangesHashAndEquals) {
   Font font = Font(nullptr, {});
   FontGlyphPair pair_1 = {