#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 pulkomandy):
The inversion is not done with an XOR, but with a negation: {{{d[0] = 255
- _p.data8[0];}}}. This is also a reversible operation: {{{255 - (255 - x)
= 255 - 255 + x = x}}}.
This formula is used when the drawing fully covers a pixel. When there is
only partial coverage, that new color is blended with the previous one:
{{{BLEND(d, 255 - _p.data8[2], 255 - _p.data8[1], 255 - _p.data8[0],
a);}}} (with a being the coverage percentage).
The BLEND macro does: {{{d[0] = ((((b - _p.data8[0]) * a) + (_p.data8[0]
<< 8)) >> 8);}}} (with "b" the new color, "a" the coverage, and _p the
initial value of the pixel). Blending in this way is not a self-reversible
operation. I don't know if we can design a reversible blend for this
purpose.
--
Ticket URL: <https://dev.haiku-os.org/ticket/10007#comment:7>
Haiku <https://dev.haiku-os.org>
Haiku - the operating system.
