Factorio Forums

Apologies for the mangled subject.

Attached is a video that depicts the disparity between "forward" (direction of item flow) and "backward" (against item flow direction) dragging. First, the video demonstrates the "backward" action by starting to drag a red underground belt on top of a red underground belt and going "backwards." While still dragging, the belt is rotated and continued to drag backwards over more underground belts, completely overwriting each underground belt. Then the test blueprint is replaced.

The next demonstration is of the "forward" action, again starting to place red belt on top of an underground belt and dragging forward. Again the corner is reached, and the belt rotated while dragging. This time, however the belt does not overwrite the next underground belt.

It's probably easier to see than describe. Embedded in the recording is a capture of the keys I'm pressing, along with mousing information (there's nothing unusual going on with it).

A slightly different way of looking at it:

Consider a straight belt line including undergrounds entrances/exits. When holding a belt matching the belt direction, if you drag along the line of the belt starting on a belt piece, underground entrance/exits are retained. But starting on an underground entrance/exit, all underground entrances/exits will be replaced with belt pieces, and belt pieces placed between them (maybe changed later to avoid obstacles). This applies whether you are dragging forwards or backwards with respect to the belt direction.

Now consider a similar line but with a corner, and the same actions. It seems the behaviour in the second case reverts to that of the first case after following the corner when dragging in the forward direction, but not when dragging in the backwards direction.

Thanks for the report, it is now fixed for the next release.