nanogui: How to change the alpha value of a pixmap?
Subject:
Re: [nanogui] How to change the alpha value of a pixmap?
From:
Greg Haerr ####@####.####
Date:
5 Jul 2012 05:34:27 -0000
Message-Id: <CF4771E7-5E20-4E85-A521-FFAC3127513F@censoft.com>
> how can I efficiently change the alpha value of all pixels in a pixmap?
> I want to do a fadein/-out effect. In a previous version I could do sth
> like this:
>
> GrCopyArea(trg, gc, 0, 0, w, h, src, 0, 0,
> MWROP_BLENDCONSTANT | (fadelevel & 0xFF));
>
> But this does not work anymore, since the constant is now fixed at 150.
Arne,
This one will be a little complicated, because of the way that all the blit
code was rewritten in 0.93. Here is a way that should make it work;
we essentially need to make room for the lower eight bits to hold
the fade level as a parameter to blendconstant, like the old version did:
1. Redefine MWROP_BLENDCONSTANT to 0x100 in mwtypes.h.
This will make room, for this ROP only, for the alpha param in the
lower 8 bits.
2. Move the code handling MWROP_BLENDCONSTANT out of the
switch statement in convblit_frameb.c to just above the switch statement,
and check for "if ((op & 0xff00) == MWROP_BLENDCONSTANT) {…} else switch ...
to handle this ROP.
3. Get the alpha value as "int alpha = op & 0xff;'"
Things should work as before. I may have forgotten something,
but that seems from visual inspection that it should work.
Regards,
Greg
