Name scale properties on Sprites to things that make sense

[DigiDuncan]

What does it do?

• Allows setting scale to a float for backwards compatible codefeel/easy proportional scaling
• Getting scale returns a tuple[float, float]
• Renames scale -> scale_x
• Renames scale_xy -> scale
• Adds scale_y

Why should this be done?

• The current implementation lies to you. scale as it is returns scale_x, which is incorrect if x/y are scaled independently.
• There is precedent. Sprite currently returns position¹ as a 2-tuple, and center_x and center_y as floats.
• Learning wrong is worse than not learning. The current implementation is more confusing for children in the long run. Most game libraries represent scale in both dimensions, and Arcade should aim to provide transferable knowledge.
• It's confusing for a developer. If you are a games dev, understanding why .scale returns x, scale_y returns y, scale_xy returns a tuple, but setting scale sets both x and y, is very confusing and makes code harder to read and reeks havoc on codefeel.

¹I'd argue position should be center as well, but that's for another day.

[pushfoo]

TL;DR: This will be a non-breaking change & efficiency upgrade with pyglet 2.1, which seems to be coming sooner than expected.

Benefits:

1. sprite_instance.scale *= 2.0 will work with scalars as it does now
2. sprite_instance.scale *= 2.0, 3.0:
   • It'll just work with arbitrary sequences (pyglet 2.1 feature)
   • Cleaner
   • More efficient than multiplying center_x and center_y individually (both iterate over and update all referencing SpriteLists)
   • More reliable than doing math on the individual axes yourself

Steps required:

• Bump to pyglet 2.1 (Switch to Pyglet 2.1 or dev releases #2043)
• Make BasicSprite.scale return pyglet 2.1's tuple-based Vec2s
• Improve doc to use/review position to teach tuples, then lead into scale
  1. cute diagram with scale x and scale y, stretching a snake image
  2. scale example with interactive GUI sliders to scale sprite
  3. add links to healthbar examples
• Revert any example temp fixes to pass CI / typing

[einarf]

What about the initializer? Should scale still only be a float there?

[pushfoo]

Imo, it could be either without an isinstance check:

if hasattr(scale, "__len__"):
    self._scale = Vec2(*scale)
else:
    self._scale = Vec2(scale, scale)