Add equator and ecliptic overlays (#109)

[alexchandel]

Summary

• add --equator and --ecliptic options for the polar projection
• render the celestial equator and ecliptic overlays
• draw the ecliptic in yellow when colors are enabled
• add test coverage for the new coordinate/rendering path
• fixes Ecliptic or polar equator? #109

[alexchandel]

@da-luce can I get a workflow approval?

[codecov]

Codecov Report

❌ Patch coverage is 94.19087% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/drawing.c	87.38%	3 Missing and 11 partials ⚠️

Files with missing lines	Coverage Δ
src/coord.c	64.91% <100.00%> (+5.72%)	⬆️
test/coord_test.c	100.00% <100.00%> (ø)
test/drawing_test.c	89.24% <100.00%> (+7.73%)	⬆️
src/drawing.c	56.17% <87.38%> (+14.13%)	⬆️

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[da-luce]

Just checked this out--awesome! I'll try and take a closer look soon to better understand the code and then merge this in

[alexchandel]

Thx! I can add some more test coverage if you need. draw_polyline_connected() is very general-purpose / arguably overkill, but was the only way I could get the corners consistently correct and I thought "why not make it general?"

[da-luce]

Thx! I can add some more test coverage if you need. draw_polyline_connected() is very general-purpose / arguably overkill, but was the only way I could get the corners consistently correct and I thought "why not make it general?"

This is exactly how I've tried approach drawing.c, so it fits right in! Would you be able to add a few more coverage tests? I know the drawing ones are annoying to make but I plan on using draw_polyline_connected() to draw a full equatorial grid sometime soon (🤞), so it'd be good for that function to have good coverage

[alexchandel]

Expanded the tests, think I got everything worth covering. Can you rerun the workflow? @codecov will you do that yourself, bot?

There might be some inspiration in render_reference_circle() to be taken for gridlines, it's somewhat general in sampling+projecting+drawing a celestial reference circle.

[alexchandel]

@da-luce needs workflow approval again apparently

[alexchandel]

There is also a bikeshedding question of -e / -E for --equator / --ecliptic. I figured "equator" was slightly more common so it got -e, but I could see it either way.

[da-luce]

I honestly don't have a huge preference, especially because I'll reorganize the API in 2.0. Stuff has been busy and I haven't had time to really look through this but I'll get it merged in the next few weeks

[alexchandel]

No rush. There are a couple corner case "partials" in the codecov still too, lmk if you need those to be covered. I've been using this build locally for a while, haven't seen any issues.

I've noticed that if it's left running for like a full day, astroterm appears behind when I check in on it. Not sure if that's because of OS sleeping, or drift in the "game loop" logic, but worth noting.