gaaclarke d7752e30c5 [Impeller] faster glyph atlas generation by removing data copies (flutter/engine#41290) ...

fixes https://github.com/flutter/flutter/issues/124996

This is the best I could come up with easily.  It doesn't give as good of a result as I'd hoped.  I measured it with a simple microbenchmark derived from one of the unit tests and it gave a 6% decrease in time ( 241.314us vs 257.626us) on macos release builds (run with rosetta).

Improvements:
1) Removed the copying of the std::set to an std::vector
1) Uses references instead of copying FontGlyphPairs out of collections in a few places
1) Holds new glyphs as a vector of references to the set instead of copying all the FontGlyphPairs
1) Deletes more lines of code than it adds

## the benchmark

```diff
diff --git a/impeller/typographer/typographer_unittests.cc b/impeller/typographer/typographer_unittests.cc
index 01a11d494c..1b99afa699 100644
--- a/impeller/typographer/typographer_unittests.cc
+++ b/impeller/typographer/typographer_unittests.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <chrono>
 #include "flutter/testing/testing.h"
 #include "impeller/playground/playground_test.h"
 #include "impeller/typographer/backends/skia/text_frame_skia.h"
@@ -149,23 +150,29 @@ TEST_P(TypographerTest, GlyphAtlasWithLotsOfdUniqueGlyphSize) {
       sk_font);
   ASSERT_TRUE(blob);
 
-  TextFrame frame;
-  size_t count = 0;
-  TextRenderContext::FrameIterator iterator = [&]() -> const TextFrame* {
-    if (count < 8) {
-      count++;
-      frame = TextFrameFromTextBlob(blob, 0.6 * count);
-      return &frame;
-    }
-    return nullptr;
-  };
-  auto atlas = context->CreateGlyphAtlas(GlyphAtlas::Type::kAlphaBitmap,
-                                         atlas_context, iterator);
-  ASSERT_NE(atlas, nullptr);
-  ASSERT_NE(atlas->GetTexture(), nullptr);
-
-  ASSERT_EQ(atlas->GetTexture()->GetSize().width * 2,
-            atlas->GetTexture()->GetSize().height);
+  auto beg = std::chrono::high_resolution_clock::now();
+  int count = 10000;
+  for (int i = 0; i < count; ++i) {
+    TextFrame frame;
+    size_t count = 0;
+    TextRenderContext::FrameIterator iterator = [&]() -> const TextFrame* {
+      if (count < 8) {
+        count++;
+        frame = TextFrameFromTextBlob(blob, 0.6 * count);
+        return &frame;
+      }
+      return nullptr;
+    };
+    auto atlas = context->CreateGlyphAtlas(GlyphAtlas::Type::kAlphaBitmap,
+                                           atlas_context, iterator);
+    ASSERT_NE(atlas, nullptr);
+    ASSERT_NE(atlas->GetTexture(), nullptr);
+    ASSERT_EQ(atlas->GetTexture()->GetSize().width * 2,
+              atlas->GetTexture()->GetSize().height);
+  }
+  auto end = std::chrono::high_resolution_clock::now();
+  auto duration = std::chrono::duration_cast<std::chrono::microseconds>(end - beg);
+  FML_LOG(ERROR) << "Elapsed Time: " << static_cast<double>(duration.count())/count << "us";
 }

```

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

2023-04-18 20:07:58 +00:00

..

src/flutter

[Impeller] faster glyph atlas generation by removing data copies (flutter/engine#41290)

2023-04-18 20:07:58 +00:00