OGL: Add GPUTimer class for measuring execution time of a draw/dispatch

Source/Core/VideoBackends/OGL/GPUTimer.h

@@ -0,0 +1,105 @@
+// Copyright 2016 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "Common/GL/GLExtensions/GLExtensions.h"
+
+#ifndef GL_TIME_ELAPSED
+#define GL_TIME_ELAPSED 0x88BF
+#endif
+
+namespace OGL
+{
+/*
+ * This class can be used to measure the time it takes for the GPU to perform a draw call
+ * or compute dispatch. To use:
+ *
+ *   - Create an instance of GPUTimer before issuing the draw call.
+ *     (this can be before or after any binding that needs to be done)
+ *
+ *   - (optionally) call Begin(). This is not needed for a single draw call.
+ *
+ *   - Issue the draw call or compute dispatch as normal.
+ *
+ *   - (optionally) call End(). This is not necessary for a single draw call.
+ *
+ *   - Call GetTime{Seconds,Milliseconds,Nanoseconds} to determine how long the operation
+ *     took to execute on the GPU.
+ *
+ * NOTE: When the timer is read back, this will force a GL flush, so the more often a timer is used,
+ * the larger of a performance impact it will have. Only one timer can be active at any time, due to
+ * using GL_TIME_ELAPSED. This is not enforced by the class, however.
+ *
+ */
+class GPUTimer final
+{
+public:
+  GPUTimer()
+  {
+    glGenQueries(1, &m_query_id);
+    Begin();
+  }
+
+  ~GPUTimer()
+  {
+    End();
+    glDeleteQueries(1, &m_query_id);
+  }
+
+  void Begin()
+  {
+    if (m_started)
+      glEndQuery(GL_TIME_ELAPSED);
+
+    glBeginQuery(GL_TIME_ELAPSED, m_query_id);
+    m_started = true;
+  }
+
+  void End()
+  {
+    if (!m_started)
+      return;
+
+    glEndQuery(GL_TIME_ELAPSED);
+    m_started = false;
+  }
+
+  double GetTimeSeconds()
+  {
+    GetResult();
+    return static_cast<double>(m_result) / 1000000000.0;
+  }
+
+  double GetTimeMilliseconds()
+  {
+    GetResult();
+    return static_cast<double>(m_result) / 1000000.0;
+  }
+
+  u32 GetTimeNanoseconds()
+  {
+    GetResult();
+    return m_result;
+  }
+
+private:
+  void GetResult()
+  {
+    if (m_has_result)
+      return;
+
+    if (m_started)
+      End();
+
+    glGetQueryObjectuiv(m_query_id, GL_QUERY_RESULT, &m_result);
+    m_has_result = true;
+  }
+
+  GLuint m_query_id;
+  GLuint m_result = 0;
+  bool m_started = false;
+  bool m_has_result = false;
+};
+}  // namespace OGL