An operating system may receive transition information indicating that a user-interface of an application is to be transitioned from a first state to a second state. Transition of the user-interface from the first state to the second state comprises a change in a property of a user-interface item. The operating system may, in response to receiving the transition information, obtain from a rendering engine a value for the property of the user-interface item corresponding to the first state. The operating system may embed a module in the rendering engine so as to detect the change in the property of the user-interface item through communication from the application to the rendering engine; and obtain from the module a respective value for the property of the user-interface item corresponding to the second state. The operating system may generate an animation based on a comparison between the value and the respective value.