No fall damage when falling up

[SpaghettiToastBook]

Issue type

• Bug report

Minetest version

0.4.17.1

Summary

If gravity is inverted, no fall damage occurs when hitting something, even if falling down from that height would induce fall damage.

[paramat]

Interesting, low priority but would be nice to be consistent.

[Wuzzy2]

For those who want to look into this, here are some pointers for you:

File: src/client/clientenvironment.cpp
Function: ClientEnvironment::step

Relevant code:

         for (const CollisionInfo &info : player_collisions) {
                 v3f speed_diff = info.new_speed - info.old_speed;;
                 // Handle only fall damage
                 // (because otherwise walking against something in fast_move kills you)
                 if (speed_diff.Y < 0 || info.old_speed.Y >= 0)
                         continue;

[Desour]

paramat wrote at #6123 (comment):

Negative gravity is possible but not really intended or supported.

[SpaghettiToastBook]

Thanks @Wuzzy2. I suppose I could try to fix it, but I have very little C++ skill...

Why isn't negative gravity supported?

[paramat]

Because it's not very useful or usable.

[SpaghettiToastBook]

It'd be useful if you had an item to toggle the sign of gravity so that you can move up faster (but also risking taking fall damage), or an item that inverts gravity while jump is pressed (producing a weird sort of flight). I actually wrote a mod that makes the latter one, which is how I found this bug.

Still, I can see why negative gravity is not really that important.

[HybridDog]

because otherwise walking against something in fast_move kills you

This makes it unrealistic. Running against a wall should not hurt you but falling from somewhere should.
Nonetheless, damage with fast_move is bad for gameplay.
To solve this predicament, you could make the player bounce back instead of loosing hearts when running against a wall. If the gravity is inverted you'd also bounce.

[Calinou]

Having fall damage when hitting a ceiling makes sense for consistency's sake as nodes with the bouncy group can push you upwards with great force.

I would still disable fall damage when hitting walls though.

[paramat]

A new issue for optional all-direction damage might appear, if it does this issue could perhaps be closed.
@SpaghettiToastBook are you requesting horizontal collision damage as well?