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The best way that I know of is to make the stairs themselves (and not railings on the side) as passable then include an invisible surface with the same slope angle as the stairs but have it as invisible. It's the simplest method.

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It's ridiculous, but this tried and true method doesn't work anymore. You can no longer use invisible level geometry for a collision hull. To achieve the same effect with c_instructions, you have to take your invisible shape and make it a map entity and then import into the level and use it that way. Then it should work.

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I agree. C_collision may be better in some aspects, but currently the OBB method puts together TWO complications.

First: with USE_BOX< collision between entities and level is made using ellipsoids. So, surface normal is taken from the ellipsoid at the collision point, and not from the surface. To illustrate this better I made this image:



This causes that the surface normal read from stairs (when the entity is gliding up) constantly changes, depending on where the ellipsoid is hitting the steps. For this reason, it's very hard to code something that really allows entity to go up stairs while preventing to glide up slopes, and vice-versa.
For instance, if we set the var move_min_z to 0.5, we prevent entities to go up very steep slopes, but it would not be able to go up quite mild stairs (as some of the 'normals' obtained at the stairs are read as even stepper than from the slopes).


So, now, more than ever, the 'invisible ramp' trick is necessary, and it would solve most issues. But.. here comes the second problem.

Second: Invisible level blocks are not detected by TRACE!
Now, this is something I have to understand. Why would I need an invisible block that is also passable, and doesn't cast shadows, and does nothing? If there's a specific flag for Passable blocks, why make invisible blocks also passable? Of course there may be internal engine details I don't know, but I can only speak from my point of view.

These two problems narrow the options we have. In the best of cases, we have to write an unnecessarily complex script to handle this.


The manual doesn't help. Although it tries:

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Block Properties: Invisible
invisible obstacles. Note that invisible blocks are also not detected by trace() instructions. If a block should be invisible, but detected by trace() , use the None texture flag instead.

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c_collision...
For these reasons the GameStudio Template Scripts use two c_move calls instead. One to handle gravity, the second to handle the forces acting on the player. This is a more flexible solution that allows for more control but is slower than a single c_move call.

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