[abenedik]

It looks like for some reason the DirectX device is removed when you minimize the window. This should not happen - Windows OS should preserve the device even when the computer goes to sleep.

This indicates a problem with the system or a driver.

Anyway, I the future I plan to improve error handling in this case (calling GetDeviceRemovedReason to get a better reason for device removal). Also, there will be an event called in such a case - to handle such situations, the user will need to save the current state of the objects, then dispose all existing DXEngine / DirectX resources and recreate the scene from scratch.