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What is the relationship between CDE and Motif? 6-Dec-00 17:00 GMT In order to answer this question, we should go back and look at the original window manager, mwm (the Motif Window Manager), and consider the services which it provided, and look at some of the problems with the implementation. In looking at the issues, we will then see why the Common Desktop Environment (CDE) came about. Mwm was a layout manager pure and simple. Its primary concern was simply to configure the stacking order of the applications on the screen, and to ensure that the focus was correctly distributed amongst the various programs as the user switched context between applications. It did not concern itself with consistency of appearance: each application was entirely free to choose whatever appearance it sought for itself, and no attempt was made to coordinate the defaults for any of the running applications. Part of the problem was the Motif toolkit as originally written: it made no attempt to rationalize appearance across the various applications which concurrently occupied the screen. Such behavior which it provided in the toolkit were basic to say the least: since the default toolkit background for certain objects was a not particularly appealing shade of blue, this meant that most application programmers would automatically assign new default colors to their application. Naturally each programmer might well consider such issues as the number of available colors supported by the hardware, and attempt to optimize the color usage of the program to hand. But none of this was coordinated: each application would provide its own defaults, and although each might be optimal in terms of color usage in its own terms, taken together with other applications on the screen it was still entirely possible to run out of colors or indeed other scarce resources, perhaps to overload the X server with an inordinately large array of fonts. The effect could be rather more than cosmetic if the appearance of certain controls like toggles, buttons, and so on, differed widely across the running applications: to a novice user, these subtle changes could be the source of confusion. Of course, the user could specify some default colors or fonts in their own X defaults files which would in principle apply to all applications. In practice, since each application generally provided its own defaults, and since configuration of X resource files is not a particularly unsophisticated task, asking the user to address the issue of coordinating sensible defaults for all applications is a distinctly sub-optimal solution. Added to which, when Motif first appeared on the scene, the paradigm for the desktop was less sophisticated: there was no notion of the virtual desktop, with its multiple rooms or whatever, which make the logical space on the desktop larger than the physical parameters of the display hardware. When mwm was first around, we were used to a scheme of working where we would have a few applications on the screen; we would generally finish one task before proceeding to the next, although there might be some multi-tasking going on. This was partly a result of moving over from dumb terminals: there, we might have had several tasks running in the background, but the foreground contained the interface of a single application. Changing to a windowing environment involved a change in mind set, and these things take time. In the (as then) new windowing environment, the screen would not be cluttered with long-running background tasks like mail programs which nowadays we tend to leave on the screen all day, along with whatever else we are doing. The screen certainly did become cluttered as we got used to the environment, and became more adept at holding multiple application contexts in our minds at the same time. Which is where the CDE project comes in. There are two aspects to CDE. Firstly, there is CDE Motif, which is a set of enhancements to the Motif toolkit which provide hooks, generally implemented at the XmDisplay and XmScreen level, such that the general default appearance of an application can be set so that it overrides some of the defaults which the application might like to assign to itself. And secondly, there is the CDE desktop manager. This provides the multi-room capability which is absent from mwm, as well as implementing things like style-manager programs so that the user can set the default colors, fonts, and so forth for all applications on the screen. Furthermore, the CDE project was a collaborative venture involving some of the more well-known operating system vendors (Sun, HP, SCO, IBM, Dec (Compaq), etc), so that the whole project also had something of a cross-platform aspect to it: it ensured a degree of consistency to the desktops across all of the vendor platforms. Although the basic design goals were known and agreed - a multi-view virtual desktop which controlled the resource usage of all applications in a consistent manner - the implementation details were sometimes not consistent. Certain things were not agreed on, like how far do you go to enforce the consistency of color usage, and whether the effect of changing the default desktop colors is dynamic or static in effect. Other platforms in parallel to the CDE effort implemented similar themes using the Motif toolkit. For example, on SGI platforms, the Schemes mechanisms are implemented in a different way to CDE on Solaris. Whatever the implementation, sometimes changing the default colors has immediate effect on all running applications, at other times the new defaults only take effect when an application is started. Then again, changing some aspects of default appearance might take effect only if you restart the desktop manager itself. These details of the design are variant. The SGI Schemes mechanisms really pre-date CDE, although some effort was made to provide a level of consistency. Schemes do, however, address the same issues as CDE. So to summarize, CDE should be viewed as an enhancement to the original Motif specification. It addresses the limitations of the original design by coordinating the resource usage of the multiple applications concurrently running on the screen. CDE Motif is simply Motif which has the extra hooks (resources) that allow the CDE window manager to set defaults for the application. Applications built under CDE Motif will run perfectly happily in a non-CDE environment: all that they lose is the connection with the CDE style management system. Sponsored by X-Designer - The Leading X/Motif GUI Builder - Click to download a FREE evaluation   Goto top of page