0000547: Walking enemies cannot leave steep slopes

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0000547: Walking enemies cannot leave steep slopes

Postby Enjay » Sun Apr 30, 2017 6:25 pm

https://mantis.zdoom.org/view.php?id=547
Summary
0000547: Walking enemies cannot leave steep slopes

Description
Enemies on a slope that is too steep to go up should be able to walk down the slope onto flat ground. They used to be able to do it but they can't any more. I'm not sure when this broke but the attached file allows the imps to walk off the slope in the last official ZDoom but not the final Git build (I know that doesn't really narrow it down much at all).

Steps To Reproduce
Load the attached demo and watch the behaviour of the imps. The cacodemon is there to show that flying enemies can cross the line at the slope bottom (so it's nothing to do with line flags) but walking enemies cannot.

Warp to map02 to see almost the same maps but the sloped sectors are set 1 unit lower. This is more like how things used to behave.

Additional Information
The slope in map01 is right on the border of what is climbable. The floors are set at 192 units high. The player cannot go up the slope and the imps cannot get off. The sloped sectors in map02 are lowered by 1 unit to 191. The player can go up and the imps can get off.

Also of passing interest, when the sloped sectors are at 192, the imps automatically slide down the slope when the map starts. Lowering the floors to 191 allows the imps to walk down the slopes at their own speed rather than being forced to slide down the slope. However, I *think* this is how things always behaved - other than in older versions when the enemies slid to the bottom of the slope, they slid right off instead of getting stuck at the bottom.

This attached file is a small section from my Burghead mod that relied on the enemies appearing on the slope, being able to come down it and ambush the player. I can modify the map if I need to but this strikes me as something that might affect other released mods too

https://mantis.zdoom.org/file_download. ... 8&type=bug
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Enjay
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Re: 0000547: Walking enemies cannot leave steep slopes

Postby Enjay » Sun Apr 30, 2017 6:26 pm

Just in case my description implied otherwise: the bug is not that the player (or anything else) cannot go up the slope - that is correct behaviour. The bug is that, even on such a steep slope, enemies should be able to leave it. It's just that being unable to leave the slope happens at the same gradient as being unable to climb it.
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Enjay
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Re: 0000547: Walking enemies cannot leave steep slopes

Postby RockstarRaccoon » Sun Apr 30, 2017 6:26 pm

Honestly, I've always felt like things should slide down slopes...
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Re: 0000547: Walking enemies cannot leave steep slopes

Postby Enjay » Sun Apr 30, 2017 6:26 pm

I'm fine with them sliding down the steep slopes (they shouldn't slide down climbable slopes though - and they don't, so that's fine) but they should be able to get off the slope and onto the flat at the bottom once they have slid down.
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Enjay
Everyone is a moon, and has a dark side which he never shows to anybody. Twain
 
 
 
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Re: 0000547: Walking enemies cannot leave steep slopes

Postby Graf Zahl » Sun Apr 30, 2017 6:26 pm

Welcome to the wonderful world of Doom engine physics... :(
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Re: 0000547: Walking enemies cannot leave steep slopes

Postby Enjay » Sun Apr 30, 2017 6:27 pm

Graham Jackson of Risen3D likened messing with Doom physics to messing with a pencil or a pyramid balancing on its point.
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Everyone is a moon, and has a dark side which he never shows to anybody. Twain
 
 
 
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Re: 0000547: Walking enemies cannot leave steep slopes

Postby RockstarRaccoon » Sun Apr 30, 2017 6:27 pm

Enjay: I haven't tested this yet, but I was thinking of applying a conveyor-belt special to the slopes I want to be slid down... You think that'll work for you?
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Re: 0000547: Walking enemies cannot leave steep slopes

Postby Enjay » Sun Apr 30, 2017 6:27 pm

Thanks for the suggestion. There are a few options that I could use to fix the map (and a conveyor might well work). I'm less concerned about my specific map because I'm going to be doing a bugfix release sometime in the not too distant future anyway. However, I think it's quite likely that this issue might affect/break other already released maps and, given that it is a change from how things used to work, I feel that it should probably be addressed engine-side if it can be.
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Enjay
Everyone is a moon, and has a dark side which he never shows to anybody. Twain
 
 
 
Joined: 15 Jul 2003
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