SF: Move HWComposerBufferCache in to CompositionEngine

This simply moves DisplayHardware/HWComposerBufferCache.* to
CompositionEngine/HwcBufferCache.*, adjusting the existing code to
reference the moved file and namespace.

This is a prelude to moving the layerBE state into CompositionEngine.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Bug: 121291683
Change-Id: Id1e907963d0453ec7beea285ab384a963c356f89
diff --git a/services/surfaceflinger/CompositionEngine/Android.bp b/services/surfaceflinger/CompositionEngine/Android.bp
index 1651cc4..ce6b06c 100644
--- a/services/surfaceflinger/CompositionEngine/Android.bp
+++ b/services/surfaceflinger/CompositionEngine/Android.bp
@@ -41,6 +41,7 @@
         "src/DisplayColorProfile.cpp",
         "src/DisplaySurface.cpp",
         "src/DumpHelpers.cpp",
+        "src/HwcBufferCache.cpp",
         "src/Layer.cpp",
         "src/Output.cpp",
         "src/OutputCompositionState.cpp",
@@ -82,6 +83,7 @@
         "tests/CompositionEngineTest.cpp",
         "tests/DisplayColorProfileTest.cpp",
         "tests/DisplayTest.cpp",
+        "tests/HwcBufferCacheTest.cpp",
         "tests/LayerTest.cpp",
         "tests/MockHWComposer.cpp",
         "tests/OutputTest.cpp",
diff --git a/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/HwcBufferCache.h b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/HwcBufferCache.h
new file mode 100644
index 0000000..b45de5a
--- /dev/null
+++ b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/HwcBufferCache.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cstdint>
+#include <vector>
+
+#include <utils/StrongPointer.h>
+
+namespace android {
+
+class GraphicBuffer;
+
+namespace compositionengine::impl {
+
+// With HIDLized hwcomposer HAL, the HAL can maintain a buffer cache for each
+// HWC display and layer.  When updating a display target or a layer buffer,
+// we have the option to send the buffer handle over or to request the HAL to
+// retrieve it from its cache.  The latter is cheaper since it eliminates the
+// overhead to transfer the handle over the trasport layer, and the overhead
+// for the HAL to clone and retain the handle.
+//
+// To be able to find out whether a buffer is already in the HAL's cache, we
+// use HWComposerBufferCache to mirror the cache in SF.
+class HwcBufferCache {
+public:
+    HwcBufferCache();
+
+    // Given a buffer queue slot and buffer, return the HWC cache slot and
+    // buffer to be sent to HWC.
+    //
+    // outBuffer is set to buffer when buffer is not in the HWC cache;
+    // otherwise, outBuffer is set to nullptr.
+    void getHwcBuffer(int slot, const sp<GraphicBuffer>& buffer, uint32_t* outSlot,
+                      sp<GraphicBuffer>* outBuffer);
+
+private:
+    // a vector as we expect "slot" to be in the range of [0, 63] (that is,
+    // less than BufferQueue::NUM_BUFFER_SLOTS).
+    std::vector<sp<GraphicBuffer>> mBuffers;
+};
+
+} // namespace compositionengine::impl
+} // namespace android
diff --git a/services/surfaceflinger/CompositionEngine/src/HwcBufferCache.cpp b/services/surfaceflinger/CompositionEngine/src/HwcBufferCache.cpp
new file mode 100644
index 0000000..6f340b9
--- /dev/null
+++ b/services/surfaceflinger/CompositionEngine/src/HwcBufferCache.cpp
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <compositionengine/impl/HwcBufferCache.h>
+#include <gui/BufferQueue.h>
+#include <ui/GraphicBuffer.h>
+
+namespace android::compositionengine::impl {
+
+HwcBufferCache::HwcBufferCache() {
+    mBuffers.reserve(BufferQueue::NUM_BUFFER_SLOTS);
+}
+
+void HwcBufferCache::getHwcBuffer(int slot, const sp<GraphicBuffer>& buffer, uint32_t* outSlot,
+                                  sp<GraphicBuffer>* outBuffer) {
+    if (slot == BufferQueue::INVALID_BUFFER_SLOT || slot < 0) {
+        // default to slot 0
+        slot = 0;
+    }
+
+    if (static_cast<size_t>(slot) >= mBuffers.size()) {
+        mBuffers.resize(slot + 1);
+    }
+
+    *outSlot = slot;
+
+    if (mBuffers[slot] == buffer) {
+        // already cached in HWC, skip sending the buffer
+        *outBuffer = nullptr;
+    } else {
+        *outBuffer = buffer;
+
+        // update cache
+        mBuffers[slot] = buffer;
+    }
+}
+
+} // namespace android::compositionengine::impl
diff --git a/services/surfaceflinger/CompositionEngine/tests/HwcBufferCacheTest.cpp b/services/surfaceflinger/CompositionEngine/tests/HwcBufferCacheTest.cpp
new file mode 100644
index 0000000..f2a1aad
--- /dev/null
+++ b/services/surfaceflinger/CompositionEngine/tests/HwcBufferCacheTest.cpp
@@ -0,0 +1,82 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <compositionengine/impl/HwcBufferCache.h>
+#include <gtest/gtest.h>
+#include <gui/BufferQueue.h>
+#include <ui/GraphicBuffer.h>
+
+namespace android::compositionengine {
+namespace {
+
+class HwcBufferCacheTest : public testing::Test {
+public:
+    ~HwcBufferCacheTest() override = default;
+
+    void testSlot(const int inSlot, const uint32_t expectedSlot) {
+        uint32_t outSlot;
+        sp<GraphicBuffer> outBuffer;
+
+        // The first time, the output  is the same as the input
+        mCache.getHwcBuffer(inSlot, mBuffer1, &outSlot, &outBuffer);
+        EXPECT_EQ(expectedSlot, outSlot);
+        EXPECT_EQ(mBuffer1, outBuffer);
+
+        // The second time with the same buffer, the outBuffer is nullptr.
+        mCache.getHwcBuffer(inSlot, mBuffer1, &outSlot, &outBuffer);
+        EXPECT_EQ(expectedSlot, outSlot);
+        EXPECT_EQ(nullptr, outBuffer.get());
+
+        // With a new buffer, the outBuffer is the input.
+        mCache.getHwcBuffer(inSlot, mBuffer2, &outSlot, &outBuffer);
+        EXPECT_EQ(expectedSlot, outSlot);
+        EXPECT_EQ(mBuffer2, outBuffer);
+
+        // Again, the second request with the same buffer sets outBuffer to nullptr.
+        mCache.getHwcBuffer(inSlot, mBuffer2, &outSlot, &outBuffer);
+        EXPECT_EQ(expectedSlot, outSlot);
+        EXPECT_EQ(nullptr, outBuffer.get());
+
+        // Setting a slot to use nullptr lookslike works, but note that
+        // the output values make it look like no new buffer is being set....
+        mCache.getHwcBuffer(inSlot, sp<GraphicBuffer>(), &outSlot, &outBuffer);
+        EXPECT_EQ(expectedSlot, outSlot);
+        EXPECT_EQ(nullptr, outBuffer.get());
+    }
+
+    impl::HwcBufferCache mCache;
+    sp<GraphicBuffer> mBuffer1{new GraphicBuffer(1, 1, HAL_PIXEL_FORMAT_RGBA_8888, 1, 0)};
+    sp<GraphicBuffer> mBuffer2{new GraphicBuffer(1, 1, HAL_PIXEL_FORMAT_RGBA_8888, 1, 0)};
+};
+
+TEST_F(HwcBufferCacheTest, cacheWorksForSlotZero) {
+    testSlot(0, 0);
+}
+
+TEST_F(HwcBufferCacheTest, cacheWorksForMaxSlot) {
+    testSlot(BufferQueue::NUM_BUFFER_SLOTS - 1, BufferQueue::NUM_BUFFER_SLOTS - 1);
+}
+
+TEST_F(HwcBufferCacheTest, cacheMapsNegativeSlotToZero) {
+    testSlot(-123, 0);
+}
+
+TEST_F(HwcBufferCacheTest, cacheMapsInvalidBufferSlotToZero) {
+    testSlot(BufferQueue::INVALID_BUFFER_SLOT, 0);
+}
+
+} // namespace
+} // namespace android::compositionengine