From c38f0b7aaee3651f0eb98c7987da420f4225f504 Mon Sep 17 00:00:00 2001
From: Jonah Williams <jonahwilliams@google.com>
Date: Thu, 13 Mar 2025 10:55:02 -0700
Subject: [PATCH] [Impeller] fix validation check when restoring to onscreen
 with BDF and mips. (#165098)

Fixes https://github.com/flutter/flutter/issues/163421

If we restore to the onscreen but need to generate mips (because its a
toImage call) then we could miss the mip map generation. This will
primarily happen on Android emulators as they do not support framebuffer
fetch.
---
 .../display_list/aiks_dl_unittests.cc         | 23 +++++++++++++++++++
 .../flutter/impeller/display_list/canvas.cc   | 23 +++++++++++++++++--
 .../flutter/impeller/display_list/canvas.h    |  4 ++++
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/engine/src/flutter/impeller/display_list/aiks_dl_unittests.cc b/engine/src/flutter/impeller/display_list/aiks_dl_unittests.cc
index e217d56155..0dae345069 100644
--- a/engine/src/flutter/impeller/display_list/aiks_dl_unittests.cc
+++ b/engine/src/flutter/impeller/display_list/aiks_dl_unittests.cc
@@ -20,6 +20,7 @@
 #include "flutter/display_list/dl_paint.h"
 #include "flutter/testing/testing.h"
 #include "fml/synchronization/count_down_latch.h"
+#include "gtest/gtest.h"
 #include "imgui.h"
 #include "impeller/base/validation.h"
 #include "impeller/core/device_buffer.h"
@@ -30,6 +31,7 @@
 #include "impeller/display_list/dl_dispatcher.h"
 #include "impeller/display_list/dl_image_impeller.h"
 #include "impeller/geometry/scalar.h"
+#include "impeller/playground/playground.h"
 
 namespace impeller {
 namespace testing {
@@ -1119,5 +1121,26 @@ TEST_P(AiksTest, DisplayListToTextureAllocationFailure) {
   EXPECT_EQ(texture, nullptr);
 }
 
+TEST_P(AiksTest, DisplayListToTextureWithMipGenerationOnGLES) {
+  if (GetBackend() != PlaygroundBackend::kOpenGLES) {
+    GTEST_SKIP() << "Only relevant for GLES";
+  }
+  DisplayListBuilder builder;
+
+  std::shared_ptr<DlImageFilter> filter =
+      DlImageFilter::MakeBlur(8, 8, DlTileMode::kClamp);
+  builder.SaveLayer(std::nullopt, nullptr, filter.get());
+  builder.Restore();
+
+  AiksContext aiks_context(GetContext(), nullptr);
+  // Use intentionally invalid dimensions that would trigger an allocation
+  // failure.
+  auto texture =
+      DisplayListToTexture(builder.Build(), ISize{10, 10}, aiks_context,
+                           /*reset_host_buffer=*/true, /*generate_mips=*/true);
+
+  EXPECT_FALSE(texture->NeedsMipmapGeneration());
+}
+
 }  // namespace testing
 }  // namespace impeller
diff --git a/engine/src/flutter/impeller/display_list/canvas.cc b/engine/src/flutter/impeller/display_list/canvas.cc
index f3f96425f1..1c60c5857e 100644
--- a/engine/src/flutter/impeller/display_list/canvas.cc
+++ b/engine/src/flutter/impeller/display_list/canvas.cc
@@ -1718,7 +1718,6 @@ bool Canvas::BlitToOnscreen(bool is_onscreen) {
   auto offscreen_target = render_passes_.back()
                               .inline_pass_context->GetPassTarget()
                               .GetRenderTarget();
-
   if (SupportsBlitToOnscreen()) {
     auto blit_pass = command_buffer->CreateBlitPass();
     blit_pass->AddCopy(offscreen_target.GetRenderTargetTexture(),
@@ -1762,6 +1761,24 @@ bool Canvas::BlitToOnscreen(bool is_onscreen) {
   }
 }
 
+bool Canvas::EnsureFinalMipmapGeneration() const {
+  if (!render_target_.GetRenderTargetTexture()->NeedsMipmapGeneration()) {
+    return true;
+  }
+  std::shared_ptr<CommandBuffer> cmd_buffer =
+      renderer_.GetContext()->CreateCommandBuffer();
+  if (!cmd_buffer) {
+    return false;
+  }
+  std::shared_ptr<BlitPass> blit_pass = cmd_buffer->CreateBlitPass();
+  if (!blit_pass) {
+    return false;
+  }
+  blit_pass->GenerateMipmap(render_target_.GetRenderTargetTexture());
+  blit_pass->EncodeCommands();
+  return renderer_.GetContext()->EnqueueCommandBuffer(std::move(cmd_buffer));
+}
+
 void Canvas::EndReplay() {
   FML_DCHECK(render_passes_.size() == 1u);
   render_passes_.back().inline_pass_context->GetRenderPass();
@@ -1775,7 +1792,9 @@ void Canvas::EndReplay() {
   if (requires_readback_) {
     BlitToOnscreen(/*is_onscreen_=*/is_onscreen_);
   }
-
+  if (!EnsureFinalMipmapGeneration()) {
+    VALIDATION_LOG << "Failed to generate onscreen mipmaps.";
+  }
   if (!renderer_.GetContext()->FlushCommandBuffers()) {
     // Not much we can do.
     VALIDATION_LOG << "Failed to submit command buffers";
diff --git a/engine/src/flutter/impeller/display_list/canvas.h b/engine/src/flutter/impeller/display_list/canvas.h
index 08273caca0..1962d48d5f 100644
--- a/engine/src/flutter/impeller/display_list/canvas.h
+++ b/engine/src/flutter/impeller/display_list/canvas.h
@@ -263,6 +263,10 @@ class Canvas {
   // Visible for testing.
   bool SupportsBlitToOnscreen() const;
 
+  /// For picture snapshots we need addition steps to verify that final mipmaps
+  /// are generated.
+  bool EnsureFinalMipmapGeneration() const;
+
  private:
   ContentContext& renderer_;
   RenderTarget render_target_;