Tl;dr: `LuaFluidBox::get_prototype()` is known to be broken and can access neither the full fluidbox prototype data nor the actual state of the fluidboxes for the current recipe. It would be nice to give it the full functionality.
What I want to accomplish
I want to read an entity and find the position of each fluidbox of this entity that has a valid connection to a neighbor. This way, I can delete the original entity and place pipes wherever it was connected.
What I tried so far
On Entity A, `LuaFluidBox::get_connected(x)` returns a list of LuaFluidBox objects that have a connection to Entity A's x'th fluidbox. Say A's #1 fluidbox is connected to B's #1 fluidbox, and both have multiple pipe connections. I can determine the location of the actual connection by computing the world coordinate of all the connection points using `fluidbox.get_prototype(1).pipe_connections` of both A and B and see which ones match up.
This breaks with assembly machines, where the fluidboxes are modified at runtime to disable or merge the pipe connections into fewer fluidboxes, so they no longer match the prototypes. There is no way to determine the location on an assembly machine of a particular pipe connection. LuaFluidBox::get_prototype() cannot retrieve all the prototypes as defined in the Data stage because its input index is erroneously limited to the number of dynamically-assigned fluidboxes, which is usually less than the number of actual prototypes.
This behavior was identified in a 2018 interface request and a 2020 "won't fix" bug report with an acknowledgement of the problem but no resolution.
1. The first intuitive solution that would be to add a method LuaFluidBox::get_pipe_connections() to return runtime-assigned pipe connections for this runtime-assigned fluidbox. I.e., when a chemical plant is set to Sulfuric Acid, get_pipe_connections(1) would return an array with two pipe_connections corresponding to the two inputs that have been merged.
2. The simplest solution may be to fix LuaFluidBox::get_prototype() so that it actually can return the complete data-stage prototype data. I.e., when a chemical plant is set to Sulfuric Acid and has two fluidboxes, get_prototype(3) and get_prototype(4) would still return the two output port definitions as they were originally defined. Then a mod could also retrieve the recipe in use, and determine for itself which prototype fluidboxes have been merged at runtime, and thus which pipe connections go to each runtime fluidbox.
3. The most comprehensive solution would be for the results of LuaFluidBox::get_connected() to include the indexes and/or location offsets of the pipe connection(s) where the two fluidboxes join.
Thank you for your consideration.
Place to ask discuss and request the modding support of Factorio. Don't request mods here.
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