Before this fix, if vsync was on the GPU cells buffer could be cleared
for a frame while resizing the terminal down. This was due to the fact
that the surface sent messages for the resize to both the renderer and
the IO thread. If the renderer thread was processed first then the GPU
cells buffer(s) would be cleared and not rebuilt, because the terminal
state would be larger than the GPU cell buffers causing updateFrame to
bail out early, leaving empty cell buffers.
This fixes the problem by changing the origin of the renderer's resize
message to be the IO thread, only after properly updating the terminal
state, to avoid clearing the GPU cells buffers at a time they can't be
successfully rebuilt.
This happened to work in releases somehow but Xcode debug builds would
catch this as an assertion. Our cell bg pipeline now uses the "full
screen vertex shader" which takes no parameters, so we don't need a
vertex descriptor.
- Significant changes to optimize memory usage.
- Adjusted formatting of the metal shader code to improve readability.
- Normalized naming conventions in shader code.
- Abstracted repetitive code for attribute descriptors to a helper
function.
With a minimum contrast set, the colored glyphs that Powerline uses
would sometimes be set to white or black while the surrounding background
colors remain unchanged, breaking up contiguous colors on segments of
the Powerline.
This no longer happens with this patch as Powerline glyphs are now
special-cased and exempt from the minimum contrast adjustment.
There are scenarios where this configuration looks bad. This commit
introduces some heuristics to prevent it. Here are the heuristics:
* Extension is always enabled on alt screen.
* Extension is disabled if a row contains any default bg color. The
thinking is that in this scenario, using the default bg color looks
just fine.
* Extension is disabled if a row is marked as a prompt (using semantic
prompt sequences). The thinking here is that prompts often contain
perfect fit glyphs such as Powerline glyphs and those look bad when
extended.
This introduces some CPU cost to the extension feature but it should be
minimal and respects dirty tracking. This is unfortunate but the feature
makes many terminal scenarios look much better and the performance cost
is minimal so I believe it is worth it.
Further heuristics are likely warranted but this should be a good
starting set.
