[Impeller] keep imgui hostbuffer alive. (flutter/engine#56409)

Fixes flutter#158275

We are now counting on the content context to keep the host buffer alive. the imgui overlay does not use a content context, so it has to manage the lifetime of the host buffer correctly, keeping it alive for as many frames as needed and destroying it in the correct order (before context destruction).

Author: Jonah Williams

engine/src/flutter/impeller/playground/imgui/imgui_impl_impeller.cc

@@ -138,13 +138,11 @@ void ImGui_ImplImpeller_Shutdown() {
 }
 
 void ImGui_ImplImpeller_RenderDrawData(ImDrawData* draw_data,
-                                       impeller::RenderPass& render_pass) {
+                                       impeller::RenderPass& render_pass,
+                                       impeller::HostBuffer& host_buffer) {
   if (draw_data->CmdListsCount == 0) {
     return;  // Nothing to render.
   }
-  auto host_buffer = impeller::HostBuffer::Create(
-      render_pass.GetContext()->GetResourceAllocator(),
-      render_pass.GetContext()->GetIdleWaiter());
 
   using VS = impeller::ImguiRasterVertexShader;
   using FS = impeller::ImguiRasterFragmentShader;
@@ -178,7 +176,7 @@ void ImGui_ImplImpeller_RenderDrawData(ImDrawData* draw_data,
   VS::UniformBuffer uniforms;
   uniforms.mvp = impeller::Matrix::MakeOrthographic(display_rect.GetSize())
                      .Translate(-display_rect.GetOrigin());
-  auto vtx_uniforms = host_buffer->EmplaceUniform(uniforms);
+  auto vtx_uniforms = host_buffer.EmplaceUniform(uniforms);
 
   size_t vertex_buffer_offset = 0;
   size_t index_buffer_offset = total_vtx_bytes;
@@ -284,5 +282,5 @@ void ImGui_ImplImpeller_RenderDrawData(ImDrawData* draw_data,
     vertex_buffer_offset += draw_list_vtx_bytes;
     index_buffer_offset += draw_list_idx_bytes;
   }
-  host_buffer->Reset();
+  host_buffer.Reset();
 }

engine/src/flutter/impeller/playground/imgui/imgui_impl_impeller.h

@@ -7,6 +7,7 @@
 
 #include <memory>
 
+#include "impeller/core/host_buffer.h"
 #include "third_party/imgui/imgui.h"
 
 namespace impeller {
@@ -23,6 +24,7 @@ IMGUI_IMPL_API void ImGui_ImplImpeller_Shutdown();
 
 IMGUI_IMPL_API void ImGui_ImplImpeller_RenderDrawData(
     ImDrawData* draw_data,
-    impeller::RenderPass& renderpass);
+    impeller::RenderPass& renderpass,
+    impeller::HostBuffer& host_buffer);
 
 #endif  // FLUTTER_IMPELLER_PLAYGROUND_IMGUI_IMGUI_IMPL_IMPELLER_H_

engine/src/flutter/impeller/playground/playground.cc

@@ -9,6 +9,7 @@
 
 #include "fml/closure.h"
 #include "fml/time/time_point.h"
+#include "impeller/core/host_buffer.h"
 #include "impeller/playground/image/backends/skia/compressed_image_skia.h"
 #include "impeller/playground/image/decompressed_image.h"
 #include "impeller/renderer/command_buffer.h"
@@ -148,6 +149,9 @@ bool Playground::IsPlaygroundEnabled() const {
 }
 
 void Playground::TeardownWindow() {
+  if (host_buffer_) {
+    host_buffer_.reset();
+  }
   if (context_) {
     context_->Shutdown();
   }
@@ -303,8 +307,13 @@ bool Playground::OpenPlaygroundHere(
         return false;
       }
       pass->SetLabel("ImGui Render Pass");
+      if (!host_buffer_) {
+        host_buffer_ = HostBuffer::Create(context_->GetResourceAllocator(),
+                                          context_->GetIdleWaiter());
+      }
 
-      ImGui_ImplImpeller_RenderDrawData(ImGui::GetDrawData(), *pass);
+      ImGui_ImplImpeller_RenderDrawData(ImGui::GetDrawData(), *pass,
+                                        *host_buffer_);
 
       pass->EncodeCommands();
 

engine/src/flutter/impeller/playground/playground.h

@@ -10,6 +10,7 @@
 
 #include "flutter/fml/status.h"
 #include "flutter/fml/time/time_delta.h"
+#include "impeller/core/host_buffer.h"
 #include "impeller/core/runtime_types.h"
 #include "impeller/core/texture.h"
 #include "impeller/geometry/point.h"
@@ -130,6 +131,7 @@ class Playground {
   std::shared_ptr<Context> context_;
   Point cursor_position_;
   ISize window_size_ = ISize{1024, 768};
+  std::shared_ptr<HostBuffer> host_buffer_;
 
   void SetCursorPosition(Point pos);
 

engine/src/flutter/testing/run_tests.py

@@ -553,7 +553,7 @@ def make_test(name, flags=None, extra_env=None):
             '--enable_vulkan_validation',
             '--enable_playground',
             '--playground_timeout_ms=4000',
-            '--gtest_filter="*ColorWheel/Vulkan"',
+            '--gtest_filter="*ColorWheel*"',
         ],
         coverage=coverage,
         extra_env=extra_env,