Jérémy Morel wrote:
Thanks to Niels, Haithem and Chris responses, the fade out effect now
works.
Chris > It looks like the DSDRAW_BLEND was the most important of all
the missing flags. Without it no alpha blending is possible. Thanks
for the indication.
I'll switch to layers when my project is over and I enter the
refinishing phase. For now I'm concentrating on making it work.
Haithem > Thanks ! Setting the pixelformat parameter without the
DSDESC_PIXELFORMAT wasn't exactly the best thing to do. And I would
have totally missed it if it weren't for you. Out of curiosity, I took
off the flag to measure its effect once blending is activated: it
gives weird results in the fading out effect. Kinda reminded me of the
of the movie "2001 a space odyssey" :)
Niels > Just adding the same layer over and over should work: the fade
out effect should be linear and end with a perfectly white image.
However it doesn't, I discovered it once the flags were correctly set.
It leaves in the end a kind of waterstamp (see attached image). I
already saw that implementing that very same effect with QT, but I
can't figure why it does so. I switched to your method, which provides
an accelerated version of the effect (from k=30 and over, the image is
back to pure white).
I can only say that I would expect this to be something outside the
realm of DirectFB/QT - like driver issues or maybe water in your
display, just thinking out loud :) I have never seen an effect like
that. You can always do "dfbdump -ds -dl" (if you are running
multi-core, otherwise you have to call an internal directfb function
from your app, check dfbdump sources what it does) to dump the current
contents of your DirectFB buffers.
I am also a bit puzzled how you expect to get a whitening effect when
you apply the color ARGB 01ffffff over and over; blending normally does
((256-a)*destination)/256 + source, so if your destination is 01010101
then ((256-a)*destination)/256 will give 00000000 (rounding down) and
adding the source will bring you back to 01010101 (default
premultiplication, as you would need for regular blending). Higher
numbers will block at other rouding error related values.
Thanks again to all 3 of you !
--
Jérémy
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