[Impeller] wire up bdf and blend detection in experimental canvas. (#53151)

Use the flags in #53104 + context capabilities to determine if we need to begin the first pass as an offscreen.

Part of flutter/flutter#142054

Author: jonahwilliams

impeller/display_list/dl_dispatcher.cc

@@ -18,10 +18,12 @@
 #include "impeller/display_list/dl_vertices_geometry.h"
 #include "impeller/display_list/nine_patch_converter.h"
 #include "impeller/display_list/skia_conversions.h"
+#include "impeller/entity/contents/content_context.h"
 #include "impeller/entity/contents/filters/filter_contents.h"
 #include "impeller/entity/contents/filters/inputs/filter_input.h"
 #include "impeller/entity/contents/runtime_effect_contents.h"
 #include "impeller/entity/entity.h"
+#include "impeller/geometry/color.h"
 #include "impeller/geometry/path.h"
 #include "impeller/geometry/path_builder.h"
 #include "impeller/geometry/scalar.h"
@@ -1170,11 +1172,24 @@ Canvas& DlDispatcher::GetCanvas() {
   return canvas_;
 }
 
-ExperimentalDlDispatcher::ExperimentalDlDispatcher(ContentContext& renderer,
-                                                   RenderTarget& render_target,
-                                                   bool requires_readback,
-                                                   IRect cull_rect)
-    : canvas_(renderer, render_target, requires_readback, cull_rect) {}
+static bool RequiresReadbackForBlends(
+    const ContentContext& renderer,
+    flutter::DlBlendMode max_root_blend_mode) {
+  return !renderer.GetDeviceCapabilities().SupportsFramebufferFetch() &&
+         ToBlendMode(max_root_blend_mode) > Entity::kLastPipelineBlendMode;
+}
+
+ExperimentalDlDispatcher::ExperimentalDlDispatcher(
+    ContentContext& renderer,
+    RenderTarget& render_target,
+    bool has_root_backdrop_filter,
+    flutter::DlBlendMode max_root_blend_mode,
+    IRect cull_rect)
+    : canvas_(renderer,
+              render_target,
+              has_root_backdrop_filter ||
+                  RequiresReadbackForBlends(renderer, max_root_blend_mode),
+              cull_rect) {}
 
 Canvas& ExperimentalDlDispatcher::GetCanvas() {
   return canvas_;

impeller/display_list/dl_dispatcher.h

@@ -12,6 +12,7 @@
 #include "impeller/aiks/experimental_canvas.h"
 #include "impeller/aiks/paint.h"
 #include "impeller/entity/contents/content_context.h"
+#include "impeller/geometry/color.h"
 
 namespace impeller {
 
@@ -291,7 +292,8 @@ class ExperimentalDlDispatcher : public DlDispatcherBase {
  public:
   ExperimentalDlDispatcher(ContentContext& renderer,
                            RenderTarget& render_target,
-                           bool requires_readback,
+                           bool has_root_backdrop_filter,
+                           flutter::DlBlendMode max_root_blend_mode,
                            IRect cull_rect);
 
   ~ExperimentalDlDispatcher() = default;

impeller/display_list/dl_playground.cc

@@ -55,7 +55,9 @@ bool DlPlayground::OpenPlaygroundHere(DisplayListPlaygroundCallback callback) {
         list->Dispatch(collector);
 
         ExperimentalDlDispatcher impeller_dispatcher(
-            context.GetContentContext(), render_target, IRect::MakeMaximum());
+            context.GetContentContext(), render_target,
+            display_list->root_has_backdrop_filter(),
+            display_list->max_root_blend_mode(), IRect::MakeMaximum());
         list->Dispatch(impeller_dispatcher);
         impeller_dispatcher.FinishRecording();
         context.GetContentContext().GetTransientsBuffer().Reset();

shell/gpu/gpu_surface_metal_impeller.mm

@@ -164,8 +164,6 @@
 
         impeller::IRect cull_rect = surface->coverage();
         SkIRect sk_cull_rect = SkIRect::MakeWH(cull_rect.GetWidth(), cull_rect.GetHeight());
-        [[maybe_unused]] auto supports_readback =
-            surface_frame.framebuffer_info().supports_readback;
 
 #if ENABLE_EXPERIMENTAL_CANVAS
         impeller::TextFrameDispatcher collector(aiks_context->GetContentContext(),
@@ -176,7 +174,9 @@
             fml::MakeCopyable([aiks_context, &display_list, &cull_rect,
                                &sk_cull_rect](impeller::RenderTarget& render_target) -> bool {
               impeller::ExperimentalDlDispatcher impeller_dispatcher(
-                  aiks_context->GetContentContext(), render_target, supports_readback, cull_rect);
+                  aiks_context->GetContentContext(), render_target,
+                  display_list->root_has_backdrop_filter(), display_list->max_root_blend_mode(),
+                  cull_rect);
               display_list->Dispatch(impeller_dispatcher, sk_cull_rect);
               impeller_dispatcher.FinishRecording();
               aiks_context->GetContentContext().GetTransientsBuffer().Reset();

shell/gpu/gpu_surface_vulkan_impeller.cc

@@ -84,8 +84,6 @@ std::unique_ptr<SurfaceFrame> GPUSurfaceVulkanImpeller::AcquireFrame(
 
         auto cull_rect =
             surface->GetTargetRenderPassDescriptor().GetRenderTargetSize();
-        [[maybe_unused]] auto supports_readback =
-            surface_frame.framebuffer_info().supports_readback;
 
         return renderer->Render(
             std::move(surface),
@@ -99,7 +97,8 @@ std::unique_ptr<SurfaceFrame> GPUSurfaceVulkanImpeller::AcquireFrame(
                   SkIRect::MakeWH(cull_rect.width, cull_rect.height));
               impeller::ExperimentalDlDispatcher impeller_dispatcher(
                   aiks_context->GetContentContext(), render_target,
-                  supports_readback,
+                  display_list->root_has_backdrop_filter(),
+                  display_list->max_root_blend_mode(),
                   impeller::IRect::RoundOut(
                       impeller::Rect::MakeSize(cull_rect)));
               display_list->Dispatch(

shell/platform/embedder/embedder_external_view.cc

@@ -117,7 +117,8 @@ bool EmbedderExternalView::Render(const EmbedderRenderTarget& render_target,
 
     impeller::ExperimentalDlDispatcher impeller_dispatcher(
         aiks_context->GetContentContext(), *impeller_target,
-        /*supports_readback=*/false, cull_rect);
+        display_list->root_has_backdrop_filter(),
+        display_list->max_root_blend_mode(), cull_rect);
     display_list->Dispatch(impeller_dispatcher, sk_cull_rect);
     impeller_dispatcher.FinishRecording();
     aiks_context->GetContentContext().GetTransientsBuffer().Reset();