Implementation of Advanced Display Technologies on HP-UX Workstations

This article provides implementation and configuration information about the single logical screen (SLS) technology described in the article “Advanced Display Technologies on HP-UX Workstations.”1 Understanding the implementation of SLS requires a little background on the X server architecture. The X server is divided into layers of functionality, each with a specific purpose and each interfacing with its neighbors. At the lowest level, which is closest to the physical hardware, is the device-dependent X (DDX) layer. This layer is responsible for controlling the frame buffer, including all rendering. Specifics of frame buffer control involve functions such as frame buffer initialization and state management, hardware locking, rendering, pointer control, hardware colormap management, and other functions such as direct memory access. Also included within the DDX layer is the detection and management of input. At the highest layer is the device-independent X (DIX) layer. This layer contains code that is independent of the various hardware platforms. Think of this layer as the control layer. It includes the dispatch loop that manages the reception and processing of X protocol, event management, error detection, and other control, organization and bookkeeping operations. This layer also interfaces extensively with the operating system interface layer and with the DDX layers. The operating system interface layer contains operating system calls, and it controls such things as memory management (allocation and deallocation), connections (socket creation), and kernel interactions. Although most of the operating system interface layer code is referenced from within the DIX layer, the DDX layer also invokes interface-layer-specific calls. Although there are other areas, such as font control, they have very little to do with SLS so they will be omitted from our discussion. Figure 1 shows typical X Client using an X API such as Xlib to communicate with the X server