skpbench: add option for gpu timing

include/private/SkGpuTimer.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkGpuTimer_DEFINED
+#define SkGpuTimer_DEFINED
+
+#include "SkTypes.h"
+#include "SkExchange.h"
+#include <chrono>
+
+using SkPlatformGpuTimerQuery = intptr_t;

[bsalomon, 2016/09/30 18:37:16]

What do you think about putting this in sk_gpu_test? It was my intention to put
the fence stuff there when I moved it tools but never followed through.

[csmartdalton, 2016/10/03 16:52:24]

Done.

+constexpr static SkPlatformGpuTimerQuery SK_InvalidGpuTimerQuery = 0;
+
+/**
+ * Platform-independent interface for timing operations on the GPU.
+ */
+class SkGpuTimer {
+public:
+    SkGpuTimer(bool disjointSupport)
+        : fDisjointSupport(disjointSupport)
+        , fActiveTimer(SK_InvalidGpuTimerQuery) {
+    }
+    virtual ~SkGpuTimer() { SkASSERT(!fActiveTimer); }
+
+    /**
+     * Returns whether this timer can detect disjoint GPU operations while timing. If false, a query
+     * has less confidence when it completes with QueryStatus::kAccurate.
+     */
+    bool disjointSupport() const { return fDisjointSupport; }
+
+    /**
+     * Inserts a "start timing" command in the GPU command stream.
+     */
+    void queueStart() {
+        SkASSERT(!fActiveTimer);
+        fActiveTimer = this->onQueueTimerStart();
+    }
+
+    /**
+     * Inserts a "stop timing" command in the GPU command stream.
+     *
+     * @return a query object that can retrieve the time elapsed once the timer has completed.
+     */
+    SkPlatformGpuTimerQuery SK_WARN_UNUSED_RESULT queueStop() {
+        SkASSERT(fActiveTimer);
+        this->onQueueTimerStop(fActiveTimer);
+        return skstd::exchange(fActiveTimer, SK_InvalidGpuTimerQuery);
+    }
+
+    enum class QueryStatus {
+        kInvalid,  //<! the timer query is invalid.
+        kPending,  //<! the timer is still running on the GPU.
+        kDisjoint, //<! the query is complete, but dubious due to disjoint GPU operations.
+        kAccurate  //<! the query is complete and reliable.
+    };
+
+    virtual QueryStatus checkQueryStatus(SkPlatformGpuTimerQuery) = 0;
+    virtual std::chrono::nanoseconds getTimeElapsed(SkPlatformGpuTimerQuery) = 0;
+    virtual void deleteQuery(SkPlatformGpuTimerQuery) = 0;
+
+private:
+    virtual SkPlatformGpuTimerQuery onQueueTimerStart() const = 0;
+    virtual void onQueueTimerStop(SkPlatformGpuTimerQuery) const = 0;
+
+    bool const                fDisjointSupport;
+    SkPlatformGpuTimerQuery   fActiveTimer;
+};
+
+#endif