[Impeller] remove CPU clear of atlas.

impeller/renderer/backend/gles/blit_command_gles.cc

@@ -276,7 +276,7 @@ bool BlitCopyBufferToTextureCommandGLES::Encode(
                   0u,                          // border
                   data.external_format,        // external format
                   data.type,                   // type
-                  tex_data                     // data
+                  nullptr                      // data
     );
     texture_gles.MarkSliceInitialized(slice);
   }

impeller/renderer/blit_pass_unittests.cc

@@ -104,5 +104,29 @@ TEST_P(BlitPassTest, ChecksInvalidSliceParameters) {
                                  std::nullopt, "", /*slice=*/0));
 }
 
+TEST_P(BlitPassTest, CanBlitSmallRegionToUninitializedTexture) {
+  auto context = GetContext();
+  auto cmd_buffer = context->CreateCommandBuffer();
+  auto blit_pass = cmd_buffer->CreateBlitPass();
+
+  TextureDescriptor dst_format;
+  dst_format.storage_mode = StorageMode::kDevicePrivate;
+  dst_format.format = PixelFormat::kR8G8B8A8UNormInt;
+  dst_format.size = {1000, 1000};
+  auto dst = context->GetResourceAllocator()->CreateTexture(dst_format);
+
+  DeviceBufferDescriptor src_format;
+  src_format.size = 4;
+  src_format.storage_mode = StorageMode::kHostVisible;
+  auto src = context->GetResourceAllocator()->CreateBuffer(src_format);
+
+  ASSERT_TRUE(dst);
+
+  EXPECT_TRUE(blit_pass->AddCopy(DeviceBuffer::AsBufferView(src), dst,
+                                 IRect::MakeLTRB(0, 0, 1, 1), "", /*slice=*/0));
+  EXPECT_TRUE(blit_pass->EncodeCommands(GetContext()->GetResourceAllocator()));
+  EXPECT_TRUE(context->GetCommandQueue()->Submit({std::move(cmd_buffer)}).ok());
+}
+
 }  // namespace testing
 }  // namespace impeller

impeller/typographer/backends/skia/typographer_context_skia.cc

@@ -142,10 +142,12 @@ static size_t PairsFitInAtlasOfSize(
                               )) {
       return pairs.size() - i;
     }
-    glyph_positions.emplace_back(Rect::MakeXYWH(location_in_atlas.x(),  //
-                                                location_in_atlas.y(),  //
-                                                glyph_size.width,       //
-                                                glyph_size.height       //
+    // The size of the glyph was padded by 1px on all sides. Shift the glyph
+    // origin by 1px so the padding surrounds the glyph.
+    glyph_positions.emplace_back(Rect::MakeXYWH(location_in_atlas.x() + 1,  //
+                                                location_in_atlas.y() + 1,  //
+                                                glyph_size.width,           //
+                                                glyph_size.height           //
                                                 ));
   }
 
@@ -180,10 +182,12 @@ static bool CanAppendToExistingAtlas(
                               )) {
       return false;
     }
-    glyph_positions.emplace_back(Rect::MakeXYWH(location_in_atlas.x(),  //
-                                                location_in_atlas.y(),  //
-                                                glyph_size.width,       //
-                                                glyph_size.height       //
+    // The size of the glyph was padded by 1px on all sides. Shift the glyph
+    // origin by 1px so the padding surrounds the glyph.
+    glyph_positions.emplace_back(Rect::MakeXYWH(location_in_atlas.x() + 1,  //
+                                                location_in_atlas.y() + 1,  //
+                                                glyph_size.width,           //
+                                                glyph_size.height           //
                                                 ));
   }
 
@@ -234,7 +238,8 @@ static void DrawGlyph(SkCanvas* canvas,
                       const Glyph& glyph,
                       bool has_color) {
   const auto& metrics = scaled_font.font.GetMetrics();
-  const auto position = SkPoint::Make(0, 0);
+  const auto position =
+      SkPoint::Make(1.0f / scaled_font.scale, 1.0f / scaled_font.scale);
   SkGlyphID glyph_id = glyph.index;
 
   SkFont sk_font(
@@ -280,6 +285,12 @@ static bool UpdateAtlasBitmap(const GlyphAtlas& atlas,
       continue;
     }
 
+    FML_DCHECK(pos->GetOrigin() != Point(0, 0));
+    // Add 1px of padding around glyph so that linearly sampled skew/rotate
+    // glyphs do not sample uninitialized data.
+    size.width += 2;
+    size.height += 2;
+
     SkBitmap bitmap;
     HostBufferAllocator allocator(host_buffer);
     bitmap.setInfo(GetImageInfo(atlas, size));
@@ -297,9 +308,11 @@ static bool UpdateAtlasBitmap(const GlyphAtlas& atlas,
 
     DrawGlyph(canvas, pair.scaled_font, pair.glyph, has_color);
 
-    if (!blit_pass->AddCopy(allocator.TakeBufferView(), texture,
-                            IRect::MakeXYWH(pos->GetLeft(), pos->GetTop(),
-                                            size.width, size.height))) {
+    // Note: the position is shifted by (1, 1) to include the padding pixels.
+    if (!blit_pass->AddCopy(
+            allocator.TakeBufferView(), texture,
+            IRect::MakeXYWH(pos->GetLeft() - 1, pos->GetTop() - 1, size.width,
+                            size.height))) {
       return false;
     }
   }
@@ -414,6 +427,7 @@ std::shared_ptr<GlyphAtlas> TypographerContextSkia::CreateGlyphAtlas(
   if (atlas_size.IsEmpty()) {
     return nullptr;
   }
+
   // ---------------------------------------------------------------------------
   // Step 4b: Find location of font-glyph pairs in the atlas. We have this from
   // the last step. So no need to do create another rect packer. But just do a
@@ -461,6 +475,7 @@ std::shared_ptr<GlyphAtlas> TypographerContextSkia::CreateGlyphAtlas(
   if (!new_texture) {
     return nullptr;
   }
+
   // The texture needs to be cleared to transparent black so that linearly
   // samplex rotated/skewed glyphs do not grab uninitialized data. We could
   // instead use a render pass to clear to transparent black, but there are