devtools: add a bad/hacky FPS counter

Author: blattersturm

code/components/devtools-five/src/DrawFPS.cpp

@@ -0,0 +1,72 @@
+#include "StdInc.h"
+#include <ConsoleHost.h>
+
+#include <imgui.h>
+
+#include <CoreConsole.h>
+
+#include <mmsystem.h>
+
+static InitFunction initFunction([]()
+{
+	static bool drawFpsEnabled;
+	static bool streamingListEnabled;
+	static bool streamingMemoryEnabled;
+
+	static ConVar<bool> drawFps("cl_drawFPS", ConVar_Archive, false, &drawFpsEnabled);
+
+	ConHost::OnShouldDrawGui.Connect([](bool* should)
+	{
+		*should = *should || drawFpsEnabled;
+	});
+
+	ConHost::OnDrawGui.Connect([]()
+	{
+		if (!drawFpsEnabled)
+		{
+			return;
+		}
+
+		auto& io = ImGui::GetIO();
+
+		static std::chrono::high_resolution_clock::duration previous;
+		static uint32_t index;
+		static std::chrono::microseconds previousTimes[6];
+
+		auto t = std::chrono::high_resolution_clock::now().time_since_epoch();
+		auto frameTime = std::chrono::duration_cast<std::chrono::microseconds>(t - previous);
+		previous = t;
+
+		previousTimes[index % std::size(previousTimes)] = frameTime;
+		index++;
+
+		ImGui::SetNextWindowBgAlpha(0.0f);
+		ImGui::SetNextWindowPos(ImVec2(10, 10), 0, ImVec2(0.0f, 0.0f));
+		ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
+
+		if (ImGui::Begin("DrawFps", nullptr, ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoInputs | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_AlwaysAutoResize))
+		{
+			if (index > 6)
+			{
+				std::chrono::microseconds total{ 0 };
+
+				for (int i = 0; i < std::size(previousTimes); i++)
+				{
+					total += previousTimes[i];
+				}
+
+				if (total.count() == 0)
+				{
+					total = { 1 };
+				}
+
+				uint64_t fps = ((uint64_t)1000000 * 1000) * std::size(previousTimes) / total.count();
+				fps = (fps + 500) / 1000;
+
+				ImGui::Text("%llufps", fps);
+			}
+		}
+
+		ImGui::End();
+	});
+});