A method of controlling rendering of computer images includes: providing first instructions to be processed at first computers, for rendering a first computer image; providing second instructions to be processed at second computers, for rendering a second computer image; receiving a user request for a change; and in response to receiving the request: regenerating the first instructions; providing first delta information to be processed at the first computers, reflecting one or more differences between the provided first instructions and the regenerated first instructions; regenerating the second instructions based on the request; providing second delta information to be processed at the second computers, reflecting one or more differences between the provided second instructions and the regenerated second instructions; receiving first rendering results from the first computers corresponding to the first delta information; and receiving second rendering results from the second computers corresponding to the second delta information.