My Ideas on Compositors

[Sam Spilsbury]

On Tue, Feb 1, 2011 at 3:32 AM, Carl-Philip Haensch
<Carl-Philip.Haensch at mailbox.tu-dresden.de> wrote:
> Hi,
>
> after a discussion on #wayland, I want to write down some ideas about
> compositor plugins for wayland at all.
>
> At first, the wayland reference implementation should be as basic as
> possible to make wayland also a choice for OpenBox users. On the other hand,
> you want to have nice effects on your screen, wobbling windows etc.
>
> So the solution would be a plugin architecture that extends the compositor
> for effects, app switchers and so on.
> My idea is a shared library that is loaded by wayland and that has a bunch
> of callbacks wayland can call.
> There will be only one .so file loaded into wayland but that's no reason to
> not implement plugin multiplexers and other interesting stuff.
>
> So what we need to design is a plugin API that lets you do everything you
> want. The compositor will have a list of procedure variables containing the
> linked callbacks of the master plugin. Each function call will be done if
> the pointer to the callback is not null. If the plugin replaces something
> (for example drawing a surface), the "native" implementation is not executed
> if there is a plugin function for it.
> Now a list of functions that will have to be in the plugin API. Please read
> through it and add things I forgot:
>  - onDrawBackground (draws the back image)
>  - onAfterDrawBackground(for background animations, panels)
>  - onSurfaceUpdate (to manipulate the position matrix of the window, called
> after you have matrix and matrix_inv)
>  - onSurfaceDraw (replaces the draw code of the display.. for wobbling
> windows)
>  - onAfterDraw (to draw notifications)
>  - onSurfaceCreate
>  - onSurfaceDelete
>  - onKeyPress (to fish out global hot keys like Alt+Tab; maybe needs events
> like up/down/press)
>  - Functions to manipulate the visibility of the surfaces
>  - Functions to request meta data from surfaces (fullscreen, maximized,
> minimized, toolbox)
>  - Functions to set size and position
>
> So the following things are possible with this plugin API:
>  - Having a clock and CPU load applets in background
>  - Multiple desktops
>  - desktop overview
>  - desktop cube
>  - whobbling windows
>  - notifications
>  - panels and window placement around the panel
>  - app switcher
>  - properly workigng fullscreen
>
> What did I forget? What do you think about the idea or the concept of
> implementing it?

It may actually be better to reduce the amount of executable code that
we're loading into the compositor and look into making as many of
these effects scripts or something. OpenGL ES allows us to most of the
effects that users have come to know and love using shaders, and if we
could have a proper architecture for getting those into the compositor
then writing effects becomes relatively easy.

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-- 
Sam Spilsbury