This completes the work for #1068. This addressed a subtle issue.
When we're using pixel->semigraphic art, we want slightly different
rendering. Essentially, imagine that we have two images, each two
pixels tall and one pixel wide. The top image is a transparent pixel
above a white pixel. The bottom image is a white pixel above a black
pixel. We'd expect the result to be two white pixels, but we can
instead get a black pixel above a white pixel. This is because the
*background* color is being merged from the bottom plane, but really
we want the *top* color. Ncvisuals are now blitted along with
information regarding which quadrants they draw over, and when
appropriate, we invert the foreground and background. Closes#1068.
Reclaim the "blitted" and "full foreground" bits in the
channels. Instead, we now write four bits, encoding the
four quadrants we might occupy as the result of a blit.
These four imply the previous two, leaving us with four
free bits remaining in the channels. This opens a clear
path to O(1)-time, zero-space blitter stacking #1068.
w00t!
For properly stacking transparent blittings (#1068), we
need tag those cells which both (1) originated in an
ncvisual operation and (2) have some transparency. For
the three affected blitters (halfblock, quadrant, and
sexblitter), call cell_set_blitted().
Rather than checking to see if there is enough space
for the crender vec following a geometry change, stash
the previous allocation, and realloc() whenever it
changes (i.e. whenever we get a resize). This brings
the crender vec back down in size if the screen gets
smaller, and seems to eliminate the problem in #1302.
Without defining a null implementation for the
USE_MULTIMEDIA=none case, we print a warning in programs
which linked against notcurses-core about not being built
with multimedia support. This warning is both (a) inaccurate
and (b) irrelevant. We can now distinguish between "no support"
(implementation != NULL) and "linked against notcurses-core"
(implementation == NULL). Move the warning to the shim.
