[Impeller] reuse texture if size and type matches (flutter#37527)

* [Impeller] reuse texture

* ++

* ++

Author: jonahwilliams

impeller/typographer/backends/skia/text_render_context_skia.cc

@@ -297,34 +297,40 @@ static std::shared_ptr<SkBitmap> CreateAtlasBitmap(const GlyphAtlas& atlas,
   return bitmap;
 }
 
-static std::shared_ptr<Texture> UploadGlyphTextureAtlas(
+static std::shared_ptr<Texture> CreateGlyphTextureAtlas(
     const std::shared_ptr<Allocator>& allocator,
-    std::shared_ptr<SkBitmap> bitmap,
     const ISize& atlas_size,
     PixelFormat format) {
   TRACE_EVENT0("impeller", __FUNCTION__);
   if (!allocator) {
     return nullptr;
   }
 
-  FML_DCHECK(bitmap != nullptr);
-  const auto& pixmap = bitmap->pixmap();
-
   TextureDescriptor texture_descriptor;
   texture_descriptor.storage_mode = StorageMode::kHostVisible;
   texture_descriptor.format = format;
   texture_descriptor.size = atlas_size;
 
-  if (pixmap.rowBytes() * pixmap.height() !=
-      texture_descriptor.GetByteSizeOfBaseMipLevel()) {
-    return nullptr;
-  }
-
   auto texture = allocator->CreateTexture(texture_descriptor);
   if (!texture || !texture->IsValid()) {
     return nullptr;
   }
   texture->SetLabel("GlyphAtlas");
+  return texture;
+}
+
+bool UploadGlyphTextureAtlas(const std::shared_ptr<Texture>& texture,
+                             std::shared_ptr<SkBitmap> bitmap) {
+  TRACE_EVENT0("impeller", __FUNCTION__);
+
+  FML_DCHECK(bitmap != nullptr);
+  const auto& pixmap = bitmap->pixmap();
+
+  auto texture_descriptor = texture->GetTextureDescriptor();
+  if (pixmap.rowBytes() * pixmap.height() !=
+      texture_descriptor.GetByteSizeOfBaseMipLevel()) {
+    return false;
+  }
 
   auto mapping = std::make_shared<fml::NonOwnedMapping>(
       reinterpret_cast<const uint8_t*>(bitmap->getAddr(0, 0)),  // data
@@ -333,9 +339,9 @@ static std::shared_ptr<Texture> UploadGlyphTextureAtlas(
   );
 
   if (!texture->SetContents(mapping)) {
-    return nullptr;
+    return false;
   }
-  return texture;
+  return true;
 }
 
 std::shared_ptr<GlyphAtlas> TextRenderContextSkia::CreateGlyphAtlas(
@@ -421,16 +427,29 @@ std::shared_ptr<GlyphAtlas> TextRenderContextSkia::CreateGlyphAtlas(
       format = PixelFormat::kR8G8B8A8UNormInt;
       break;
   }
-  auto texture = UploadGlyphTextureAtlas(GetContext()->GetResourceAllocator(),
-                                         bitmap, atlas_size, format);
-  if (!texture) {
-    return nullptr;
-  }
 
   // ---------------------------------------------------------------------------
   // Step 8: Record the texture in the glyph atlas.
+  //
+  // If the last_texture is the same size and type, reuse this instead of
+  // creating a new texture.
   // ---------------------------------------------------------------------------
-  glyph_atlas->SetTexture(std::move(texture));
+  auto old_texture = last_atlas->GetTexture();
+  if (old_texture != nullptr &&
+      old_texture->GetTextureDescriptor().size == atlas_size &&
+      old_texture->GetTextureDescriptor().format == format) {
+    if (!UploadGlyphTextureAtlas(old_texture, bitmap)) {
+      return nullptr;
+    }
+    glyph_atlas->SetTexture(std::move(old_texture));
+  } else {
+    auto texture = CreateGlyphTextureAtlas(GetContext()->GetResourceAllocator(),
+                                           atlas_size, format);
+    if (!texture || !UploadGlyphTextureAtlas(texture, bitmap)) {
+      return nullptr;
+    }
+    glyph_atlas->SetTexture(std::move(texture));
+  }
 
   return glyph_atlas;
 }

impeller/typographer/typographer_unittests.cc

@@ -137,6 +137,34 @@ TEST_P(TypographerTest, GlyphAtlasIsRecycledIfUnchanged) {
   ASSERT_EQ(atlas_context->GetGlyphAtlas(), atlas);
 }
 
+TEST_P(TypographerTest, GlyphAtlasTextureIsRecycledIfUnchanged) {
+  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 skellingtons", sk_font);
+  ASSERT_TRUE(blob);
+  auto atlas =
+      context->CreateGlyphAtlas(GlyphAtlas::Type::kAlphaBitmap, atlas_context,
+                                TextFrameFromTextBlob(blob));
+  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 a nearly identical blob.
+
+  auto blob2 = SkTextBlob::MakeFromString("spooky skellington2", sk_font);
+  auto next_atlas =
+      context->CreateGlyphAtlas(GlyphAtlas::Type::kAlphaBitmap, atlas_context,
+                                TextFrameFromTextBlob(blob2));
+  ASSERT_NE(atlas, next_atlas);
+  auto* second_texture = next_atlas->GetTexture().get();
+
+  ASSERT_EQ(second_texture, first_texture);
+}
+
 TEST_P(TypographerTest, GlyphAtlasWithLotsOfdUniqueGlyphSize) {
   auto context = TextRenderContext::Create(GetContext());
   auto atlas_context = std::make_shared<GlyphAtlasContext>();