I written the following SFML.NET app. It draw a single 128x128 sprite on the screen.

RenderWindow window = new RenderWindow(new VideoMode(800, 600), "SFML window");
window.SetVerticalSyncEnabled(true);

Texture texture = new Texture("test.jpg");    
Sprite sprite = new Sprite(texture);

// Start the game loop
while (window.IsOpen())
{
    window.DispatchEvents();
    window.Clear();
    window.Draw(sprite);
    window.Display();
}

Since VSync is enabled, the number of FPS is capped to 60. I expect the program to use very little CPU, but under task manager it show me that is use about 50% (two cores fully actually). Also it seems it use about 30% kernel time and the rest is user time.

The exact same application in SDL (just drawing a single sprite) use about 0% (regardless SDL_RENDERER_ACCELERATED is used or not).

I written the following SFML.NET app. It draw a single 128x128 sprite on the screen.

RenderWindow window = new RenderWindow(new VideoMode(800, 600), "SFML window");
window.SetVerticalSyncEnabled(true);

Texture texture = new Texture("test.jpg");    
Sprite sprite = new Sprite(texture);

// Start the game loop
while (window.IsOpen())
{
    window.DispatchEvents();
    window.Clear();
    window.Draw(sprite);
    window.Display();
}

Since VSync is enabled, the number of FPS is capped to 60. I expect the program to use very little CPU, but under task manager it show me that is use about 50% (two cores fully actually). Also it seems it use about 30% kernel time and the rest is user time.

The exact same application in SDL (just drawing a single sprite) use about 0% (regardless SDL_RENDERER_ACCELERATED is used or not).

EDIT : surprisingly, if I let the app run for a given amount of time (let's say 10-20 seconds, the CPU usage fall down to 0%). I manage to repeat this several times. That is really strange.