feat/stars

[thombruce]

closes #25

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Internal use. Do not delete.

• Tests passing
• Coverage sufficient
• Manual review
• No A11y regression
• Translations provided or not needed

[thombruce]

We have circular orbits that will have different orbital periods dependent upon the distance from the parent star.

That's enough to call this good enough for now.

In theory, I know how to implement Kepler orbits, but we might want to shift focus towards generating more than just the two planets we can do right now (maybe by porting Deep-Fold's Pixel Planet Generator and associated shaders to Bevy).

Implementing Kepler orbits would require knowledge about the planet's apoapsis and periapsis or its semi-major axis which can be derived from those. These are extra values to generate. I believe we also need knowledge of the central body's mass, though I am unsure of this.

Happy to plough forwards into different waters and circle back. There is an open issue for Kepler Orbits here: #28

[thombruce]

Actually, there is a major problem that needs to be resolved before merging.

Because the position in an orbit is calculated for a given real value of time, when the player pauses for any length of time and then unpauses the planet will jump forwards in its orbit.

We need to setup a different timer. One that takes into account the pausing and unpausing.

[thombruce]

This might be outdated, but the way to do this as of 0.9 was to create a stopwatch I think. Reference here: https://bevy-cheatbook.github.io/features/time.html#stopwatch

The stopwatch counts up from some time value that we could save and load ("game time") and needs to be manually ticked in an update function. Manual ticking means we can opt to manually not tick too, e.g. when in the pause state.

That's what we need to implement. A game_time system ticking a stopwatch which we can reference to get the time ticked in an unpaused state since game start.

That should do it.

[thombruce]

Yup, 4af11b8, that's fixed it!