sprite group classes > support source_rect functionality

[JovialKnoll]

Currently the LayeredDirty class blits sprites taking into account DirtySprite's source_rect attribute. I would like all of the groups to take into account any Sprite's source_rect attribute.

pros: I think it would be useful for all groups to use a source_rect value if present, to enable easy e.g. sprite sheet functionality.
cons: checking another attribute per sprite per draw, I don't think this will have a big performance impact but maybe that's a particular concern.

Questions about approach:

1. Is this worthwhile for me to work on, or is there no interest in a change like this?
2. Should I just put source_rect (defaulted to None) on the Sprite class so we can assume it exists, or should I not assume it exists and get it with getattr(spr, 'source_rect', None) or similar?

Thanks for reading! I'd love to get feedback.

[Starbuck5]

to enable easy e.g. sprite sheet functionality.

If one is using a sprite sheet, wouldn't it be easier to just cut out the part of the surface that should be part of the sprite? You can use .subsurface for it without even using any additional memory.

[JovialKnoll]

sure, was just an example.

Is the source_rect functionality not useful to have built in for things like that and should only remain in DirtySprite for backwards compatibility reasons?

[JovialKnoll]

Separately, for sprite sheet animations, is it better to just change source_rect over time or keep reassigning image to a different subsurface of the base surface?

[Starbuck5]

It seems most straightforward to keep re-assigning image, since that's how animations work in all other contexts, right?

[JovialKnoll]

Okay, does it make sense to support source_rect dynamically in the other draw functions at all, or is this basically just functionality we don't need and it only needs to remain available for DirtySprite to not break backwards compatibility?

If the former I can make a different PR, if the latter, please go ahead and close this issue and I'll remove the PR.