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How to create usplash themes
============================
Usplash in its current incarnation allows for simple and advanced themes. I'll
start with explaining the basics of a theme and will introduce the more advanced
topics later. I do assume that the reader has basic C programming knowledge and
knows what a Makefile is for.
A basic theme
=============
A basic theme consist of a background picture and color/position definitions for
various elements. The usplash-theme.h file lists all of them (ignore the
function pointers for now). If you specify only a background image and
color/position variables, usplash will take care of drawing a basic progress bar
and the text. The included usplash-testcard-theme.c is such a basic theme
The image you use should have max. 256 colors. The resolution is up to you, but
keep in mind that usplash will use the resolution of the image without checking
whether your display supports it. For themes that are to be default for many
people, I recommend choosing no higher than 800x600. The utility 'pngtousplash'
can be used to convert an image to usplash-usable C code. The example-theme
directory contains a complete them that builds out-of-source. Inspect its
Makefile to see how to put the pieces together. If you intend to create a
package, make sure to Build-Depend on usplash-dev, which contains pngtousplash
and the necessary header files.
You should always allow your theme to display text, the INPUT function of
usplash will display text, even when not running verbose.
Themes have a ratio field where you can specify either USPLASH_4_3 if the image
is a true 4:3 image or 16:9 if the image is a 16:9 image, scaled to 4:3. The
image MUST be a 4:3 image, because usplash can only handle 4:3 video modes
currently.
Optional 1: Custom font
=======================
You can include a custom font. You will need to link it into your theme .so file
and set the .font field in the theme structure. The example theme supplies a
custom font, so once again: look there. The font should be a bdf font, converted
with bdftousplash.
Optional 2: Custom drawing functions and animation
==================================================
Themes can override the functions called for displaying the progress bar and/or
text. This can be used to create better looking progress bar. If you supply a
custom progress bar, you're sort of forced to implement custom animations too,
since the animation code is also used for displaying a pulsating progress bar.
25 times per second, the animation function is called. This function has one
argument: whether the progress bar is currently pulsating or not. This allows
you to create animated themes as well as simply doing a better looking progress
bar.
If you override the custom drawing functions, please make sure that any images
you use, use the exact same palette as the background image. You can do this by
creating one big image containing all components and then cutting out the
respctive images or by following the instructions on
http://carol.gimp.org/gimp/resources/palettes/howto.html
For now, you should not override draw_text, because the INPUT function of
usplash will not use it and thus the txt will look odd in you theme.
The included example theme uses custom animation for the progress bar, so once
again it can be used as an example.
Optional 3: Multiple themes in one file
=======================================
Usplash theme librarys can contain multiple themes in a linked list. Each theme
has a next pointer, which should either be NULL or point to another theme in the
same file. The example theme includes the same theme at three different
resolutions.
The first theme in the list should still be called usplash_theme and it should
be the fallback variant of your theme, lowest resolution and 4:3 scale. This
because usplash will use the first theme in case no favorable resolution was
specified on th command line.
The theme selection will also take the ratio of your screen into account, so it
will favor a low-res 16:9 variant over a high-res 4:3 variant if you have a 16:9
screen.
--
Sept. 6 2006
Dennis Kaarsemaker <dennis@ubuntu.com>
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