A user mode device driver interface (UMDDI) is disclosed. The UMDDI is preferably implemented in Windows® NT® version 5.0 and similar systems. The UMDDI allows a device driver to execute in user-mode while the graphics engine (GRE) remains in kernel-mode. The UMDDI exists as a layer between the user-mode driver and GRE; from the perspective of GRE, it encapsulates the user-mode driver and makes it appear to be a normal kernel-mode driver. The UMDDI layer handles the kernel-to-user and user-to-kernel transitions, parameter validation, and management of the kernel-mode and user-mode data and objects.