In some cases you are already working with a cairo_t and know
your destination image size, this adds an API that allows you
to handle these cases more easily. Along with now being able to
draw images with an alpha level. It also leaves the original API
unchanged.
Unfortunately we can't use logging.h directly from conky as its
in C++ and lua bindings only have access to a C compiler.
Instead we now have a very simple C implementation of logging.h to
use within the bindings.
This change also adds NULL checks to catch some extra invalid
states
Previously if the source image was a different to the displayed
image the alpha channel was incorrect, as it wasn't scaled leading
to a series of artifacts.
One problem is, that tolua/lua does not handle plain data pointers
properly. Therefore something like
local surface = cairo_image_surface_create_for_data(
imlib_image_get_data_for_reading_only(), ..
will fail using the lua bindings. Hence this wrapper, which adds
a function which be used to draw an imlib image to a cairo surface.
This also addresses another issue, drawing images with a transparent
background (e.g. gifs or pngs) to the cairo surface properly. Apparently
the image format of imlib is incompatible to cairos which uses
pre-multiplied data. This is also explained in the cairo documentation.
A fix for this issue is to blend the image with another alpha mask to
get the correct values. The code and explanation for this was taken from
http://lists.cairographics.org/archives/cairo/2008-March/013492.html
Executive Summary: This wrapper function can load (transparent) images
(e.g. gif or png) from a file by using imlib and draw them on a cairo
surface.
