[Impeller] reuse texture

impeller/typographer/backends/skia/text_render_context_skia.cc

@@ -4,6 +4,7 @@
 
 #include "impeller/typographer/backends/skia/text_render_context_skia.h"
 
+#include <iostream>
 #include <utility>
 
 #include "flutter/fml/logging.h"
@@ -297,34 +298,41 @@ 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()) {
+    std::cerr << "descriptor mismatch" << std::endl;
+    return false;
+  }
 
   auto mapping = std::make_shared<fml::NonOwnedMapping>(
       reinterpret_cast<const uint8_t*>(bitmap->getAddr(0, 0)),  // data
@@ -333,9 +341,10 @@ static std::shared_ptr<Texture> UploadGlyphTextureAtlas(
   );
 
   if (!texture->SetContents(mapping)) {
-    return nullptr;
+    std::cerr << "contents cant be set" << std::endl;
+    return false;
   }
-  return texture;
+  return true;
 }
 
 std::shared_ptr<GlyphAtlas> TextRenderContextSkia::CreateGlyphAtlas(
@@ -421,16 +430,34 @@ 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) {
+    std::cerr << "reuse atlas" << std::endl;
+    if (!UploadGlyphTextureAtlas(old_texture, bitmap)) {
+      return nullptr;
+    }
+    glyph_atlas->SetTexture(std::move(old_texture));
+  } else {
+    std::cerr << "can't reuse "
+              << (old_texture != nullptr
+                      ? old_texture->GetTextureDescriptor().size
+                      : ISize(0, 0))
+              << " : " << atlas_size << std::endl;
+    auto texture = CreateGlyphTextureAtlas(GetContext()->GetResourceAllocator(),
+                                           atlas_size, format);
+    if (!texture || !UploadGlyphTextureAtlas(texture, bitmap)) {
+      return nullptr;
+    }
+    glyph_atlas->SetTexture(std::move(texture));
+  }
 
   return glyph_atlas;
 }