ncplane_as_rgba ought work for quadrants and sextants

[dankamongmen]

ncplane_rgba() currently only works on halfblocks and fullblocks (spaces). it ought be able to handle NCBLIT_2x2 and NCBLIT_3x2 as well. since we don't know what the original blit was (and they could technically be mixed), translate cells into their LCMs: each cell ought thus go to 2x6. that kinda whacks out aspect ratio; we could perhaps go to 6x12 instead?

fullblock -> 6x12
halfblocks -> 6x6, 6x6
quadrant -> 3x6, 3x6, 3x6, 3x6
sextant -> 3x4, 3x4, 3x4, 3x4, 3x4, 3x4

[dankamongmen]

this leads directly to #1441.

[dankamongmen]

we also now need NCBLIT_PIXEL support

[dankamongmen]

also, apparently it has no support for transparency, egads

[dankamongmen]

This work is ongoing in the dankamongmen/ncplane-as-rgba branch, and ought be done this evening. One thing to add: if a plane has a null glyph at a cell, we probably ought use the default character there. This allows, for instance, ncplane_as_rgba() to be run on a plane which has been filled using ncplane_set_base().

[dankamongmen]

This work is ongoing in the dankamongmen/ncplane-as-rgba branch, and ought be done this evening. One thing to add: if a plane has a null glyph at a cell, we probably ought use the default character there. This allows, for instance, ncplane_as_rgba() to be run on a plane which has been filled using ncplane_set_base().

if we want to do this, i think a better way might be to have ncplane_at_yx() consult the base cell, which is honestly probably a good idea unless we've specified otherwise in the documentation.

[dankamongmen]

also, it needs to keep working with NCBLIT_DEFAULT. except how can it? NCBLIT_DEFAULT resolves to a different thing based off the scaling type, and the latter is not available to us. hrmmm. we could always go for the most complex; since we would decay to 2x1 to maintain aspect ratio...no, because 3x2 doesn't contain 2x1 (2x2 does, though), so if they went with STRETCH and got 3x2, that won't work for a 2x1, shit...hrmm....maybe we don't allow NCBLIT_DEFAULT? maybe we prescan? maybe we go with 3x2, and retry with 2x2? no really great solutions here...

[dankamongmen]

we now support NCBLIT_2x2 and NCBLIT_3x2. we need add support for NCBLIT_BRAILLE and NCBLIT_PIXEL still, but we've genericized it to use the inverse tables from blitset.