[ Thanks to Bryan for this link.
]
“In most embedded designs, the X Window System is
overkill, especially when running a dedicated graphics
application. For this reason, the Microwindows Project was
developed. Microwindows is an open source project aimed at
producing desktop-quality graphics functionality for small
devices. The architecture allows for ease in adding different
display, mouse, touchscreen and keyboard devices, as I will explain
below. Starting with Linux version 2.2.0, the kernel contains code
to allow user applications to access graphical display memory as a
framebuffer, which ends up being a memory-mapped region in a user
process space that, when written to, controls the display
appearance. This allows graphics applications to be written without
having to have knowledge of the underlying graphics hardware, or
use the X Window System. This is the way that Microwindows
typically runs on embedded systems.”
“Microwindows was designed to attempt to bring applications to
market quickly, with a minimum of effort. In order to accomplish
this, I felt that designing yet another graphics applications
programming interface (API) would steepen the learning curve, thus
discouraging interest and increasing time-to-market. Microwindows
implements two popular graphics programming interfaces: the
Microsoft Windows Win32/WinCE graphics display interface (GDI),
used by all Windows CE and Win32 applications, and an Xlib-like
interface, known as Nano-X, used at the lowest level by all Linux
X11 widget sets. This allows the extremely large group of Windows
programmer talent to be used in developing the graphical side of
the application, as well as being familiar to the core group of
Linux graphics programmers used to working with X11.”
“Microwindows runs in 50-250k of memory, an order of magnitude
smaller than the X Window System. This is primarily the result of
using a single routine for each of the drawing functions in the
engine layer. The engine layer checks for clipping and calls a
driver-level routine for drawing a pixel or line if unclipped. The
X Window System duplicates the entire drawing routine for each
pixel depth and has clipped and unclipped versions for speed.
Microwindows fully supports the new Linux kernel framebuffer
architecture, and currently has support for 1, 2, 4, 8, 16, 24, and
32 bits per pixel displays, with support for palettized and
truecolor display color implementations, as well as grayscale. With
both APIs, all colors are specified in the portable RGB format, and
the system has routines to convert to the nearest available color,
or shade of gray for monochromatic systems. Although Microwindows
fully supports Linux, it’s internal, portable architecture is based
on a relatively simple screen device interface, and can run on many
different RTOS’s as well as bare hardware. This brings a big
benefit: graphics programming by the customer can be shared between
projects, and even run on different targets with different RTOS’s,
without having to rewrite the graphics side of the
application.”