Suggestions for Mask methods to enhance usability of mask.overlap()

[AnRibo]

It is easy to obtain a point of overlap between sprites/masks, but obtaining e.g. the right-most point of overlap specifically can be quite challanging. By default with pygame, as I understand it, I generally get the top-left-most point as it searches columns top->bottom starting with the left-most column. *edit: I took a peek at the code which seem to have various algotithms for getting a fast result depending on the situation, thus it seems best to make an alternate method to do what I want. I will try to make it myself + a working example of what it does, let me know it there is any interrest to add it to the project.

[celeritydesign]

Any extra options for specifying the start position within a mask for collision checks would be welcome.
An example use case could be in the case of a laser “beam” weapon (I.e a line, not a bullet) that overlaps an enemy. At the moment it isn’t trivial to show the closest point of impact (and truncate the beam accordingly)

[AnRibo]

Any extra options for specifying the start position within a mask for collision checks would be welcome. An example use case could be in the case of a laser “beam” weapon (I.e a line, not a bullet) that overlaps an enemy. At the moment it isn’t trivial to show the closest point of impact (and truncate the beam accordingly)

Yes, this is exactly what I mean! I have it planned out, just need to get set up with dev build and compiling. I will post progress here.

[AnRibo]

I have realized that actually coding this myself will not happen and I understand if there is noone else able/willing to do it as this highly specialized bit-manipulation in C is not something you just learn by doing, oh well I gave it a shot lol.
Instead I will cheat by flipping and offsetting the sprites to get the overlap point I want. However, if the sprites are larger than the wordsize the mask bits are stored in we still get unexpected behaviour as the current algorithm searches word-sized strips left->right and thus it will not always return the left-most overlaps. As the wordsize is different on windows and Linux we get different behaviours depending on operating system (current_algorithm.gif , explore the code example on windows and Linux to observe this difference). To completely negate this one would also have to subsurface sprites to limit height to the minimum wordsize and check them in order. So the issue is fully solvable with python at runtime, I will eventually share it by adding it to the example code, although awkwardly complex and extremely expensive compared to a fully deterministic algorithm in C. The proposed algorithm would run somewhat slower than the current algorithm and thus should not replace it, but would be a nice addition and something that no other engine/framework has as far as I know. It would also solve the current issue of unexpected results and differences between operating systems relating to wordsize (proposed_additional_algorithm.gif) and allow the user to easily place visual effects at the apropiate point of impact.

Edit: Subsurfacing does NOT work to effectively increase the wordlength. Current algorithm will decide to switch search direction after checking x strips (I guess the zag in "zig-zag" comment in the code) based on some relationship between mask/overlap/word size (???) so I can get certain sprite sizes to work but not others (unless I subsurface with a height of 1 of course).

Edit 2: I am starting to think that there are issues with how the code runs on Windows. On Linux I can subsurface to limit sprite height to below wordsize and it behaves completely deterministicly, but on Windows I get all sorts of weird unexpected behaviour.

[AnRibo]

I made an example/demo of three methods for improving mask overlap-based collision (hollow, flipped and sliced mask) where a combination of flipped and hollow gives exactly the results I need. It would be easier if we had flip/rotate methods for masks as we have with surface so I would very much like to see that in the future.
mask_collision_enhanced.py at https://github.com/AnRibo/pygame-resources