[1.1.80] Splitters do not exchange lines

[HornedHeck]

Description

I tried to create few belt balancers with custom ratio and to test them created a stand which fully loads belts. During the tests some inconsistency in splitters behaviour has been found.

Actual result

Further investigation revealed that in case if splitter is fed with 2 fully loaded lines and 2 lines ready for output 3 different mode of work possible:
1. Splitter lefts lanes as they were before:

Do nothing

Screenshot_20230523_134730.png (2.65 MiB) Viewed 589 times

2. Splitter swap lines entirely:

Swap lines

Screenshot_20230523_135324.png (2.2 MiB) Viewed 589 times

3. Splitter mixes 2 lines:

Work as expected

Screenshot_20230523_140432.png (2.67 MiB) Viewed 589 times

Expected result

I expect that splitter will mix lines (way 3), because they do so under lower loads with same usecases.

Consistency

I tried to reproduce it with all 3 tiers of belts and seems that this behaviour is quite common for yellow and red belts.
Blue belts usually works as expected but issue still can be reproduced

Way to reproduce

From the scratch:
1. Ensure you have 2 fully loaded belts of the same tier as splitter but do not connect them
2. Ensure splitter have 2 connected outputs and items will not stuck there
3. Connect 2 inputs to the splitter
4. In case if bug still can't be observed check load on inputs and pause one of them for a short period of time (e.g. remove belt and place again)
5. Repeat p. 4 until it happens, it may takes 4-5 attempts with blue belts.

Using provided save:
1. Load with the save
2. Follow p.4 and p.5 from the instruction above. You can toggle belts with constant combinators.

[boskid]

Thanks for the report however that is Not a bug. Splitter receives 2 full belts and outputs 2 full belts, everything is working as expected. There are solutions to guarantee mixing as you expect but they are using more than 1 splitter.

[HornedHeck]

Thanks for the report however that is Not a bug. Splitter receives 2 full belts and outputs 2 full belts, everything is working as expected. There are solutions to guarantee mixing as you expect but they are using more than 1 splitter.

Which of 3 ways has been expected? And why behaviour is so different compared to not full belts?

[boskid]

None of the 3 possible outcomes is preferred. There are actually 4 distinct outcomes since there are 2 cases for left lines and 2 cases for right lines: they are either passed through or swapped, so 2x2 = 4. Exact outputs selected are based on the previous state of a splitter, it simply remembers "last item was transfered to left output belt, lets try to transfer next item onto right output belt" and that decision happens separately for left lines of left and right belt and separately for right lines of the left and right belt.