From 362d0cb3ab27f730847ad4f467b114e449457f63 Mon Sep 17 00:00:00 2001
From: Jonah Williams <jonahwilliams@google.com>
Date: Mon, 11 Dec 2023 16:08:51 -0800
Subject: [PATCH] [Impeller] recycle glyph atlas texture more aggressively.
 (#48888)

If we need to remake the glyph atlas texture but the size is the same, then reuse the old texture.

For more context, see https://github.com/flutter/flutter/issues/138798 which is much slower in Impeller. This change does not fix the problem by itself.
---
 .../backends/skia/typographer_context_skia.cc | 14 +++++++
 impeller/typographer/typographer_unittests.cc | 37 ++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/impeller/typographer/backends/skia/typographer_context_skia.cc b/impeller/typographer/backends/skia/typographer_context_skia.cc
index e3082678d541a..b5a9decf15b43 100644
--- a/impeller/typographer/backends/skia/typographer_context_skia.cc
+++ b/impeller/typographer/backends/skia/typographer_context_skia.cc
@@ -446,6 +446,20 @@ std::shared_ptr<GlyphAtlas> TypographerContextSkia::CreateGlyphAtlas(
   }
   atlas_context_skia.UpdateBitmap(bitmap);
 
+  // If the new atlas size is the same size as the previous texture, reuse the
+  // texture and treat this as an updated that replaces all glyphs.
+  if (last_atlas && last_atlas->GetTexture()) {
+    std::shared_ptr<Texture> last_texture = last_atlas->GetTexture();
+    if (atlas_size == last_texture->GetSize()) {
+      if (!UpdateGlyphTextureAtlas(bitmap, last_texture)) {
+        return nullptr;
+      }
+
+      glyph_atlas->SetTexture(last_texture);
+      return glyph_atlas;
+    }
+  }
+
   // ---------------------------------------------------------------------------
   // Step 7b: Upload the atlas as a texture.
   // ---------------------------------------------------------------------------
diff --git a/impeller/typographer/typographer_unittests.cc b/impeller/typographer/typographer_unittests.cc
index 343c172b4121f..38ac599e6b95f 100644
--- a/impeller/typographer/typographer_unittests.cc
+++ b/impeller/typographer/typographer_unittests.cc
@@ -9,7 +9,6 @@
 #include "impeller/typographer/backends/skia/typographer_context_skia.h"
 #include "impeller/typographer/lazy_glyph_atlas.h"
 #include "impeller/typographer/rectangle_packer.h"
-#include "third_party/skia/include/core/SkData.h"
 #include "third_party/skia/include/core/SkFont.h"
 #include "third_party/skia/include/core/SkFontMgr.h"
 #include "third_party/skia/include/core/SkRect.h"
@@ -339,6 +338,42 @@ TEST_P(TypographerTest, RectanglePackerAddsNonoverlapingRectangles) {
   ASSERT_EQ(packer->percentFull(), 0);
 }
 
+TEST_P(TypographerTest, GlyphAtlasTextureIsRecycledWhenContentsAreRecreated) {
+  auto context = TypographerContextSkia::Make();
+  auto atlas_context = context->CreateGlyphAtlasContext();
+  ASSERT_TRUE(context && context->IsValid());
+  SkFont sk_font = flutter::testing::CreateTestFontOfSize(12);
+  auto blob = SkTextBlob::MakeFromString("ABCDEFGHIJKLMNOPQRSTUVQXYZ123456789",
+                                         sk_font);
+  ASSERT_TRUE(blob);
+  auto atlas = CreateGlyphAtlas(
+      *GetContext(), context.get(), GlyphAtlas::Type::kColorBitmap, 32.0f,
+      atlas_context, *MakeTextFrameFromTextBlobSkia(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 a completely different textblob.
+  // everything should be different except for the underlying atlas texture.
+
+  auto blob2 = SkTextBlob::MakeFromString("abcdefghijklmnopqrstuvwxyz123456789",
+                                          sk_font);
+  auto next_atlas = CreateGlyphAtlas(
+      *GetContext(), context.get(), GlyphAtlas::Type::kColorBitmap, 32.0f,
+      atlas_context, *MakeTextFrameFromTextBlobSkia(blob2));
+  ASSERT_NE(atlas, next_atlas);
+  auto* second_texture = next_atlas->GetTexture().get();
+
+  auto new_packer = atlas_context->GetRectPacker();
+
+  ASSERT_EQ(second_texture, first_texture);
+  ASSERT_NE(old_packer, new_packer);
+}
+
 }  // namespace testing
 }  // namespace impeller