From 9f75d34bb87be08ac57b6eee49e030f836bc7b3a Mon Sep 17 00:00:00 2001
From: Ben Doherty <bendoherty@google.com>
Date: Wed, 8 Dec 2021 13:35:54 -0800
Subject: [PATCH] Rework color history in preparation for SSR (#4932)

---
 filament/src/PostProcessManager.cpp |  9 ++-----
 filament/src/PostProcessManager.h   |  1 +
 filament/src/Renderer.cpp           | 40 ++++++++++++++++++++++++++++-
 filament/src/details/Renderer.h     |  3 +++
 4 files changed, 45 insertions(+), 8 deletions(-)

diff --git a/filament/src/PostProcessManager.cpp b/filament/src/PostProcessManager.cpp
index 026706b575..4fbef7c253 100644
--- a/filament/src/PostProcessManager.cpp
+++ b/filament/src/PostProcessManager.cpp
@@ -2177,19 +2177,17 @@ void PostProcessManager::prepareTaa(FrameHistory& frameHistory,
 
 FrameGraphId<FrameGraphTexture> PostProcessManager::taa(FrameGraph& fg,
         FrameGraphId<FrameGraphTexture> input, FrameHistory& frameHistory,
+        FrameGraphId<FrameGraphTexture> colorHistory,
         TemporalAntiAliasingOptions const& taaOptions,
         ColorGradingConfig colorGradingConfig) noexcept {
 
     FrameHistoryEntry const& entry = frameHistory[0];
-    FrameGraphId<FrameGraphTexture> colorHistory;
     mat4f const* historyProjection = nullptr;
-    if (UTILS_UNLIKELY(!entry.color.handle)) {
+    if (UTILS_UNLIKELY(!colorHistory)) {
         // if we don't have a history yet, just use the current color buffer as history
         colorHistory = input;
         historyProjection = &frameHistory.getCurrent().projection;
     } else {
-        colorHistory = fg.import("TAA history", entry.colorDesc,
-                FrameGraphTexture::Usage::SAMPLEABLE, entry.color);
         historyProjection = &entry.projection;
     }
 
@@ -2296,9 +2294,6 @@ FrameGraphId<FrameGraphTexture> PostProcessManager::taa(FrameGraph& fg,
                     colorGradingSubpass(driver, colorGradingConfig);
                 }
                 driver.endRenderPass();
-
-                // perform TAA here using colorHistory + input -> output
-                resources.detach(data.output, &current.color, &current.colorDesc);
             });
     return colorGradingConfig.asSubpass ? taa->tonemappedOutput : taa->output;
 }
diff --git a/filament/src/PostProcessManager.h b/filament/src/PostProcessManager.h
index 111d235416..74c626cc9a 100644
--- a/filament/src/PostProcessManager.h
+++ b/filament/src/PostProcessManager.h
@@ -126,6 +126,7 @@ public:
 
     FrameGraphId<FrameGraphTexture> taa(FrameGraph& fg,
             FrameGraphId<FrameGraphTexture> input, FrameHistory& frameHistory,
+            FrameGraphId<FrameGraphTexture> colorHistory,
             TemporalAntiAliasingOptions const& taaOptions,
             ColorGradingConfig colorGradingConfig) noexcept;
 
diff --git a/filament/src/Renderer.cpp b/filament/src/Renderer.cpp
index b03ea974f1..52d5628b2e 100644
--- a/filament/src/Renderer.cpp
+++ b/filament/src/Renderer.cpp
@@ -589,7 +589,25 @@ void FRenderer::renderJob(ArenaScope& arena, FView& view) {
 
     // TAA for color pass
     if (taaOptions.enabled) {
-        input = ppm.taa(fg, input, view.getFrameHistory(), taaOptions, colorGradingConfig);
+        input = ppm.taa(fg, input, view.getFrameHistory(),
+                getColorHistory(fg, view.getFrameHistory()), taaOptions, colorGradingConfig);
+    }
+
+    struct ExportColorHistoryData {
+        FrameGraphId<FrameGraphTexture> color;
+    };
+    if (taaOptions.enabled) {
+        fg.addPass<ExportColorHistoryData>("Export color history", [&](FrameGraph::Builder& builder,
+                auto& data) {
+            // We need to use sideEffect here to ensure this pass won't be culled. The "output" of
+            // this pass is going to be used during the next frame as an "import".
+            builder.sideEffect();
+            data.color = builder.sample(input);
+        }, [&view](FrameGraphResources const& resources, auto const& data, backend::DriverApi&) {
+            FrameHistory& frameHistory = view.getFrameHistory();
+            FrameHistoryEntry& current = frameHistory.getCurrent();
+            resources.detach(data.color, &current.color, &current.colorDesc);
+        });
     }
 
     // --------------------------------------------------------------------------------------------
@@ -1248,6 +1266,26 @@ void FRenderer::initializeClearFlags() {
             | TargetBufferFlags::DEPTH_AND_STENCIL;
 }
 
+FrameGraphId<FrameGraphTexture> FRenderer::getColorHistory(FrameGraph& fg,
+        FrameHistory const& frameHistory) noexcept {
+    // Here we import the previous frame's color output and cache it in the blackboard. This ensures
+    // we only import it once per frame even across multiple calls to getColorHistory.
+    Blackboard& blackboard = fg.getBlackboard();
+
+    if (auto history = blackboard.get<FrameGraphTexture>("colorHistory")) {
+        return history;
+    }
+
+    FrameHistoryEntry const& entry = frameHistory[0];
+    if (UTILS_UNLIKELY(!entry.color.handle)) {
+        return {};
+    }
+    FrameGraphId<FrameGraphTexture> colorHistory = fg.import("Color history", entry.colorDesc,
+            FrameGraphTexture::Usage::SAMPLEABLE, entry.color);
+    blackboard["colorHistory"] = colorHistory;
+    return colorHistory;
+}
+
 // ------------------------------------------------------------------------------------------------
 // Trampoline calling into private implementation
 // ------------------------------------------------------------------------------------------------
diff --git a/filament/src/details/Renderer.h b/filament/src/details/Renderer.h
index 13626266f4..026915e8ad 100644
--- a/filament/src/details/Renderer.h
+++ b/filament/src/details/Renderer.h
@@ -187,6 +187,9 @@ private:
         return clock::now() - getUserEpoch();
     }
 
+    static FrameGraphId<FrameGraphTexture> getColorHistory(FrameGraph& fg,
+            FrameHistory const& frameHistory) noexcept;
+
     // keep a reference to our engine
     FEngine& mEngine;
     FrameSkipper mFrameSkipper;