[2.1.20] Poor performance when hovering over entity with many circuit network signals

[Redruin]

Hovering over power poles/combinators with very many actively changing circuit signals reduces UPS + FPS significantly when the total number of unique signals is many thousand:

09-29-2026, 16-00-11.png (698.55 KiB) Viewed 213 times

Notably, this performance cost is asymmetric compared to other GUIs in the game - only hovering specifically seems to significantly degrade performance.

Here is a sample blueprint showcasing the issue that isn't purely academic. It uses a Lookup table to calculate the square root of an integer in a single tick (using a technique which could be reused for any monotonic function). Behind it is a simple counter to stimulate it every tick.

09-29-2026, 15-58-59.png (998.79 KiB) Viewed 213 times

Paste the blueprint into a new save, leaving the signal parameters empty.

Hovering over one of the CCs/Deciders will cause the game to "hitch" (presumably as it builds a snapshot of the large signal network to display), but will otherwise remain at full speed as long as the signal network is static. Turning on the circuit with the leftmost CC and hovering over the offending combinators however brings my FPS/UPS down to ~20/40 on my machine. Interestingly, opening the GUI of either the decider or the CC does not incur the same performance penalty, with or without the circuit updating.

This is a minor issue since it is only present when hovering, which is usually infrequent. Still, having the game hitch when mousing over circuitry is undesirable, and perhaps could be fixed quite simply due to the other GUIs being blazingly fast.

[Rseding91]

Thanks for the report. I've made some improvements to the logic for the next release which address most but not all of the performance hit from this setup.