[haiku-bugs] Re: [Haiku] #10007: OP_INVERT and anti-aliasing don't play together
- From: "Pete" <trac@xxxxxxxxxxxx>
- Date: Thu, 08 Dec 2016 01:05:45 -0000
#10007: OP_INVERT and anti-aliasing don't play together
----------------------------------+----------------------------
Reporter: Pete | Owner: stippi
Type: bug | Status: assigned
Priority: normal | Milestone: R1
Component: Kits/Interface Kit | Version: R1/Development
Resolution: | Keywords:
Blocked By: | Blocking:
Has a Patch: 0 | Platform: All
----------------------------------+----------------------------
Comment (by Pete):
Replying to [comment:5 pulkomandy]:
It looks like removing the calls to BLEND_INVERT could work.
Alternatively, we could tweak that function so that its operation is
reversible, so we can get antialiasing without leaving artifacts on the
background.
Looking more closely, I don't think just removing BLEND_INVERT would do
the job. If you examine the pixels of an anti-aliased, slightly-slanted,
line, you can see fairly large sections where there is no 100% (a=255)
coverage of any written pixel. You'd get gaps in the drawing. As
OP_INVERT is being fed the anti-aliased data, there's not much can be done
about that.
I think letting BLEND_INVERT draw pixels above a certain threshold
coverage would work. It seems reasonable that 50% (>127) is probably the
right threshold.
(Thinking more about some kind of "scaled invertible blend", I think
you're right and that it's not possible. Trying to invert less than all
the bits leads to crazy values.)
Also, I don't think that setting alpha to 255, as the current code does,
is correct. This is not reversible. I'd prefer that alpha was just left
alone.
So here's a suggested minimal rewrite of thos macros. (I've switched to
exclusive-or because I can't see any problem.)
{{{
// BLEND_INVERT
// (threshold may be arbitrary. leave alpha unchanged)
#define BLEND_INVERT(d, a) \
if (a > 127) { \
d[0] = 255 ^ d[0]; \
d[1] = 255 ^ d[1]; \
d[2] = 255 ^ d[2]; \
}
// ASSIGN_INVERT
// (leave alpha unchanged)
#define ASSIGN_INVERT(d) \
{ \
d[0] = 255 ^ d[0]; \
d[1] = 255 ^ d[1]; \
d[2] = 255 ^ d[2]; \
}
}}}
Obviously the threshold check could be done in the invoking code rather
than the macro, and the two could probably be merged a bit, but I don't
have the ability to build a test ATM, so I'll leave it there.
--
Ticket URL: <
https://dev.haiku-os.org/ticket/10007#comment:8>
Haiku <
https://dev.haiku-os.org>
Haiku - the operating system.
Other related posts:
