Add Fps class
Add a class to wrap a fps value. This is useful because across
the code we
- convert between vsyncPeriod and fps
- compare with tolerance (this ensures we use consistent tolerance)
- consistent toString method
Bug: 159590486
Test: presubmit
Change-Id: Iebb77a33a2f822056642aa61bd6fac6514aa656d
diff --git a/services/surfaceflinger/Fps.h b/services/surfaceflinger/Fps.h
new file mode 100644
index 0000000..38a9af0
--- /dev/null
+++ b/services/surfaceflinger/Fps.h
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2020 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 <cmath>
+#include <ostream>
+#include <string>
+
+#include <android-base/stringprintf.h>
+#include <utils/Timers.h>
+
+namespace android {
+
+// Value which represents "frames per second". This class is a wrapper around
+// float, providing some useful utilities, such as comparisons with tolerance
+// and converting between period duruation and frequency.
+class Fps {
+public:
+ static constexpr Fps fromPeriodNsecs(nsecs_t period) { return Fps(1e9f / period, period); }
+
+ Fps() = default;
+ explicit constexpr Fps(float fps)
+ : fps(fps), period(fps == 0.0f ? 0 : static_cast<nsecs_t>(1e9f / fps)) {}
+
+ constexpr float getValue() const { return fps; }
+
+ constexpr nsecs_t getPeriodNsecs() const { return period; }
+
+ bool equalsWithMargin(const Fps& other) const { return std::abs(fps - other.fps) < kMargin; }
+
+ // DO NOT use for std::sort. Instead use comparesLess().
+ bool lessThanWithMargin(const Fps& other) const { return fps + kMargin < other.fps; }
+
+ bool greaterThanWithMargin(const Fps& other) const { return fps > other.fps + kMargin; }
+
+ bool lessThanOrEqualWithMargin(const Fps& other) const { return !greaterThanWithMargin(other); }
+
+ bool greaterThanOrEqualWithMargin(const Fps& other) const { return !lessThanWithMargin(other); }
+
+ bool isValid() const { return fps > 0.0f; }
+
+ int getIntValue() const { return static_cast<int>(std::round(fps)); }
+
+ // Use this comparator for sorting. Using a comparator with margins can
+ // cause std::sort to crash.
+ inline static bool comparesLess(const Fps& left, const Fps& right) {
+ return left.fps < right.fps;
+ }
+
+ // Compares two FPS with margin.
+ // Transitivity is not guaranteed, i.e. a==b and b==c doesn't imply a==c.
+ // DO NOT use with hash maps. Instead use EqualsInBuckets.
+ struct EqualsWithMargin {
+ bool operator()(const Fps& left, const Fps& right) const {
+ return left.equalsWithMargin(right);
+ }
+ };
+
+ // Equals comparator which can be used with hash maps.
+ // It's guaranteed that if two elements are equal, then their hashes are equal.
+ struct EqualsInBuckets {
+ bool operator()(const Fps& left, const Fps& right) const {
+ return left.getBucket() == right.getBucket();
+ }
+ };
+
+ inline friend std::string to_string(const Fps& fps) {
+ return base::StringPrintf("%.2ffps", fps.fps);
+ }
+
+ inline friend std::ostream& operator<<(std::ostream& os, const Fps& fps) {
+ return os << to_string(fps);
+ }
+
+private:
+ friend std::hash<android::Fps>;
+
+ constexpr Fps(float fps, nsecs_t period) : fps(fps), period(period) {}
+
+ float getBucket() const { return std::round(fps / kMargin); }
+
+ static constexpr float kMargin = 0.001f;
+ float fps = 0;
+ nsecs_t period = 0;
+};
+
+static_assert(std::is_trivially_copyable_v<Fps>);
+
+} // namespace android
+
+namespace std {
+template <>
+struct hash<android::Fps> {
+ std::size_t operator()(const android::Fps& fps) const {
+ return std::hash<float>()(fps.getBucket());
+ }
+};
+} // namespace std
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