Modify the default UE4 C++ project to be able to draw on the floor

I want to make a game in Unreal Engine and I need a starting point. All I need you to do is change the default C++ project so you can draw on the floor with your mouse, editing the texture. This requires a ray trace to find the point you're drawing at and then setting the texture color at that point to white. You have to use C++, not Blueprints. You may change the standard floor to a plane. Mouse look must be disabled so you can move your mouse without rotating the camera.