mirror of
https://github.com/apache/nuttx.git
synced 2026-08-05 14:19:03 +00:00
d4c904d949
Included documentation for the framebuffer example, fb. This includes a description of how the program works, what features it supports and images of what the rendered output should look like if everything is correct. Signed-off-by: Matteo Golin <matteo.golin@gmail.com>
68 lines
2.5 KiB
ReStructuredText
68 lines
2.5 KiB
ReStructuredText
==================
|
|
``fb`` Framebuffer
|
|
==================
|
|
|
|
This application is a simple demonstration which serves to test the
|
|
:doc:`framebuffer character driver
|
|
</components/nxgraphics/framebuffer_char_driver>`.
|
|
|
|
The program interacts with the framebuffer through the interfaces described in
|
|
the linked page in order to render a very simple image consisting of 6
|
|
concentric, colourful rectangles. Note that between each rectangle, the program
|
|
sleeps for 500 milliseconds. Rectangle are drawn from outermost to innermost, in
|
|
descending size.
|
|
|
|
.. figure:: fb-image.jpg
|
|
:figwidth: 80%
|
|
:align: center
|
|
:alt: The Pinephone displaying concentric, colourful rectangles after running the ``fb`` example.
|
|
|
|
The image displayed by the ``fb`` example, shown on the Pinephone. Credit to
|
|
Lup Yuen Lee.
|
|
|
|
.. warning::
|
|
|
|
The application renders directly to the framebuffer provided by the character
|
|
driver. On some devices, the entire rendering operation may not be complete
|
|
in time for the video synchronization, causing screen tearing or skips. This
|
|
is the case for the :doc:`Raspberry Pi 4B
|
|
</platforms/arm64/bcm2711/boards/raspberrypi-4b/index>`, and the results can
|
|
be seen below.
|
|
|
|
.. figure:: fb-skip.png
|
|
:figwidth: 40%
|
|
:align: center
|
|
:alt: The framebuffer example output, but with skipped pixels.
|
|
|
|
The framebuffer example output, but with skipped pixels.
|
|
|
|
Skipping issues like this one can generally be avoided by rendering to a
|
|
separate buffer first, and then copying that buffer to the framebuffer in one
|
|
operation.
|
|
|
|
Feature support
|
|
---------------
|
|
|
|
The application ignores the pixel format provided by the framebuffer character
|
|
driver, and only inspects the 'bits per pixel' (depth) field. Currently, only
|
|
the following bits per pixel are supported (with the corresponding formats
|
|
assumed):
|
|
|
|
* 1: Monochrome
|
|
* 8: RGB_332
|
|
* 16: RGB_565
|
|
* 24: RGB
|
|
* 32: ARGB
|
|
|
|
The program supports different features depending on the characteristics of the
|
|
framebuffer driver. If the framebuffer requires ``FB_UPDATE``, this example
|
|
behaves accordingly.
|
|
|
|
If the framebuffer supports ``FB_OVERLAY``, then the application also supports
|
|
getting and displaying the overlay information.
|
|
|
|
If the virtual y resolution is double that of the y resolution when the
|
|
framebuffer is initially queried, the application will attempt to use
|
|
double-buffer rendering by fetching a second framebuffer corresponding to the
|
|
``display + 1``, where ``display`` is the display number that was associated
|
|
with the first framebuffer.
|