Bouncing projectiles may fail to bounce off of 3D floors

Thu Oct 15, 2020 8:01 am

It appears that with a particular setup of 3D floors, bouncing projectiles will sometimes fail to bounce off of them. Instead, they will explode. This may be exclusive to sloped 3D floors, although I haven't been able to confirm it so far.

I've encountered this bug in the beginning area of the map Warp House. However, since that map is particularly complex, I've copied the map parts that exhibit buggy behavior to an isolated test map, which is attached to this report.

To reproduce the bug, load the test map and grab the plasma gun, which has been modified to fire bouncing projectiles. Fire at the surface in front of you (with hexagon tiles), and you'll notice that almost all projectiles explode immediately instead of bouncing.

Tested in GZDoom 4.3.1, 4.4.2, and g4.5pre-256
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Re: Bouncing projectiles may fail to bounce off of 3D floors

Thu Oct 15, 2020 12:34 pm

I've encountered this issue myself too, and I can confirm it's exclusive to sloped floors only.

Re: Bouncing projectiles may fail to bounce off of 3D floors

Thu Oct 15, 2020 12:48 pm

Sloped math is not the most robust thing out there, Doom's naive collision detection does not play that well with them.

Re: Bouncing projectiles may fail to bounce off of 3D floors

Thu Oct 15, 2020 2:11 pm

Do note that even though the 3D floors in the example WAD are sloped, projectiles fail to bounce off of their top sides, which are flat. Firing at the (sloped) underside of the structure, however, appears to also trigger the bug, but from my experience it seems to happen less often.