MenuApplets: Add CPUGraph, our first menu applet :^)

This implements the WSCPUMonitor functionality in a separate process.

MenuApplets/CPUGraph/main.cpp

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+#include <AK/CircularQueue.h>
+#include <LibCore/CProcessStatisticsReader.h>
+#include <LibCore/CTimer.h>
+#include <LibDraw/GraphicsBitmap.h>
+#include <LibGUI/GApplication.h>
+#include <LibGUI/GPainter.h>
+#include <LibGUI/GWindowServerConnection.h>
+
+NonnullRefPtr<GraphicsBitmap> create_shared_bitmap(const Size& size)
+{
+    ASSERT(GWindowServerConnection::the().server_pid());
+    ASSERT(!size.is_empty());
+    size_t pitch = round_up_to_power_of_two(size.width() * sizeof(RGBA32), 16);
+    size_t size_in_bytes = size.height() * pitch;
+    auto shared_buffer = SharedBuffer::create_with_size(size_in_bytes);
+    ASSERT(shared_buffer);
+    shared_buffer->share_with(GWindowServerConnection::the().server_pid());
+    return GraphicsBitmap::create_with_shared_buffer(GraphicsBitmap::Format::RGBA32, *shared_buffer, size);
+}
+
+static void get_cpu_usage(unsigned& busy, unsigned& idle)
+{
+    busy = 0;
+    idle = 0;
+
+    auto all_processes = CProcessStatisticsReader::get_all();
+
+    for (auto& it : all_processes) {
+        for (auto& jt : it.value.threads) {
+            if (it.value.pid == 0)
+                idle += jt.times_scheduled;
+            else
+                busy += jt.times_scheduled;
+        }
+    }
+}
+
+int main(int argc, char** argv)
+{
+    GApplication app(argc, argv);
+
+    Size applet_size(30, 16);
+    Rect applet_rect({}, applet_size);
+
+    CircularQueue<float, 30> cpu_history;
+
+    i32 applet_id = GWindowServerConnection::the().send_sync<WindowServer::CreateMenuApplet>(applet_size)->applet_id();
+    auto bitmap = create_shared_bitmap(applet_size);
+
+    GWindowServerConnection::the().send_sync<WindowServer::SetMenuAppletBackingStore>(applet_id, bitmap->shared_buffer_id());
+
+    unsigned last_busy = 0;
+    unsigned last_idle = 0;
+
+    auto repaint = [&] {
+        unsigned busy;
+        unsigned idle;
+        get_cpu_usage(busy, idle);
+        unsigned busy_diff = busy - last_busy;
+        unsigned idle_diff = idle - last_idle;
+        last_busy = busy;
+        last_idle = idle;
+        float cpu = (float)busy_diff / (float)(busy_diff + idle_diff);
+        cpu_history.enqueue(cpu);
+
+        GPainter painter(*bitmap);
+        painter.fill_rect(applet_rect, Color::Black);
+        int i = cpu_history.capacity() - cpu_history.size();
+        for (auto cpu_usage : cpu_history) {
+            painter.draw_line(
+                { applet_rect.x() + i, applet_rect.bottom() },
+                { applet_rect.x() + i, (int)(applet_rect.y() + (applet_rect.height() - (cpu_usage * (float)applet_rect.height()))) },
+                Color::from_rgb(0xaa6d4b));
+            ++i;
+        }
+
+        GWindowServerConnection::the().send_sync<WindowServer::InvalidateMenuAppletRect>(applet_id, applet_rect);
+    };
+
+    repaint();
+
+    auto timer = CTimer::construct(1000, [&] {
+        repaint();
+    });
+
+    return app.exec();
+}