[2.0.72] Underground belt lighting inconsistent when sideloading

[Thezwarteridder]

Hi, today I was playing factorio today (as one does) and noticed that west facing underground belts and sideloading west facing underground belts have significant differences in their shading on the hood.

screenshot-tick-302941.png (387.07 KiB) Viewed 289 times

This is most noticeable on the west facing variant of all underground belts however, there is a slight disparity in the east facing underground belts too though this one is much more subtle (literally just the top row of pixels and third rivet) as seen in the image below.

screenshot-tick-279568.png (408.75 KiB) Viewed 289 times

This effect is most noticeable when placing and removing the belts as seen in this video.

lighting bug.mp4

(14.87 MiB) Downloaded 20 times

The bug only occurs when a north facing transport belt touches a west/east facing underground belt, it does not occur with any other orientation of belt or underground belt. This was tested with all orientations and tiers of belts and undergrounds available in base game (green belts untested) and it occurs with all of them identically.
Aditionally the bug occurs regardless of how sideloading occurs no matter if by transport belt, underground belt or splitter so long as it is done by a north facing belt as shown in this image.

screenshot-tick-360361.png (1.06 MiB) Viewed 289 times

Have a great day Wube
- Astrid and Nia

[eugenekay]

That is an intentional "cutout" in the hood of the Underground Belt that only appears when a (ghost) belt is placed in that specific location. Any pixel-level differences are because they are different sprites - the smaller (sideloading) hood casts a smaller shadow; so this seems very consistent.

underground-belt-structure.png (143.41 KiB) Viewed 275 times

Note the extra sprites on the 3rd/4th row of data/base/graphics/entity/underground-belt/underground-belt-structure.png, and the corresponding direction_in/out_side_loading property in base/prototypes/entity/transport-belts.lua.

This cutout makes it so that items do not visually "clip through" the hood when sideloading is used:

12-18-2025, 22-09-05.png (62.15 KiB) Viewed 271 times

Good Luck!

[haon899]

As seen in your sprite sheet above the error that is being discussed is also visible there.

We are talking about the shadow cast by the metal corner trim onto the yellow hood. That is much darker on the sideloaded sprite and lighter on the standard sprite.

To be clear we are not talking about the obviously intentional cutout on the sprite. but as the title of the bug indicates, and the reference videos and text indicates we are disusing the lighting inconsistency with the shadows on the sprite.

I've added a box around it for you to see.

Added Clarificaiton.png (27.55 KiB) Viewed 146 times

As clearly visible, the underground has a much lighter shading in its standard form, but a much sharper lighting on its side-loaded form.