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[Hangedman]

Cross-pollinated from the FP forums, because I realized I could throw this open to anyone, really. This isn't so much a Flashpunk question as a general programming question.

I'm making a fancy platformer, and attempting to code in two different floors: solid floors, and drop floors (floors that you can drop through by pressing 'down', that are only solid when you are on top of them.)

But no matter how I try to program it, I always get errors where my character is clipping through the floors and getting stuck, or just falling through. I've played with the player hitboxes, the floor hitboxes, the physics/clipping code...

Can someone elaborate the most practical method for doing this?
I can do the code, I just can't figure out a good method.

[Skofo]

This is how I'd do it:

When you press down, set a variable that corresponds to the y coordinate right under your character. In the collision code between the character and floor, make it check if the floor intersects with that y coordinate--if it does, then quit the function before the actual collision code. Reset the variable once the character stands on another floor.

You might need to turn that y coordinate into a range of y coordinates if you have slopes or something.

[Rob Lach]

If you are constantly in the colliding state (ie when you're standing on something), set the player's y-coord relative to what the player is colliding with from below and keep it like that until you explicitly leave that stae (by running off the side (x-coord check) or jumping or getting attacked, whatever). That way if it moves up/down you'll player will just be glued to it. You can do something similar for x if you want platforms that move sideways.

[Tycho Brahe]

I assume there's some kind of flag for setting collisions? If there is, then how about, when the down key is pressed, setting that flag to false (no collision) until the characters y is more than the height of the character below It?

[Matt Thorson]

Here's how I do this:

First, I have two distinct types of solids: SOLID and JUMPTHRU. SOLID is completely solid, the player will never be inside it. JUMPTHRU the player can enter from below or beside but not above. So if the player is fully above a JUMPTHRU and moving downward and hits it, he stops. If the player is even one pixel within a JUMPTHRU he will not collide with it moving downward, and he never collides with it in any other direction.

Then, if the player is standing on a JUMPTHRU holding the down key and he presses jump, just drop him down one pixel and the collision system will take care of him falling.

[Hangedman]

Here's how I do this:

First, I have two distinct types of solids: SOLID and JUMPTHRU. SOLID is completely solid, the player will never be inside it. JUMPTHRU the player can enter from below or beside but not above. So if the player is fully above a JUMPTHRU and moving downward and hits it, he stops. If the player is even one pixel within a JUMPTHRU he will not collide with it moving downward, and he never collides with it in any other direction.

Then, if the player is standing on a JUMPTHRU holding the down key and he presses jump, just drop him down one pixel and the collision system will take care of him falling.

This was essentially what I attempted to do, except I ran into issues with detecting collision with a full-sized hitbox. Essentially, my character gets stuck in the floor because without multiple hitboxes...

Crap. I just figured out how to do it!
Only collide in the usual way (x, y+1), but not when he's intersecting it in any other way.
I know that seems like common sense, but I've been looking for too many complex solutions to have thought straight until now.

Thanks for the advice everyone!

[deemen]

I've found the best way to handle this kind of platform is with a state machine setup. You want to be able to prevent "tunnelling" in your physics, and this helps with that.

Basically you create two states "above" and "below". If the player is above, then he collides with the platform. If he's below, he doesn't. You use the line segment representing the top of the platform to handle the state changes.

Code:

1   |    2    |   3
    |         |     
----===========----
    |         |      
4   |    5    |   6

(Equal sign is the platform. Other lines show different areas)

Basically you make a state machine where 1, 2, 3 are "above" and 4, 5, 6 are "below". Then you allow state changes both ways for 1 <=> 4 and 3 <=> 6 but only one way for 2 and 5, 5 => 2.

Then, to handle the Drop Floor problem, all you do is swap the state to "below" and the character will stop colliding with the platform.

Hope that helps, even if you already found your solution .

[Matt Thorson]

Here's how I do this:

First, I have two distinct types of solids: SOLID and JUMPTHRU. SOLID is completely solid, the player will never be inside it. JUMPTHRU the player can enter from below or beside but not above. So if the player is fully above a JUMPTHRU and moving downward and hits it, he stops. If the player is even one pixel within a JUMPTHRU he will not collide with it moving downward, and he never collides with it in any other direction.

Then, if the player is standing on a JUMPTHRU holding the down key and he presses jump, just drop him down one pixel and the collision system will take care of him falling.

This was essentially what I attempted to do, except I ran into issues with detecting collision with a full-sized hitbox. Essentially, my character gets stuck in the floor because without multiple hitboxes...

Crap. I just figured out how to do it!
Only collide in the usual way (x, y+1), but not when he's intersecting it in any other way.
I know that seems like common sense, but I've been looking for too many complex solutions to have thought straight until now.

Thanks for the advice everyone!

  Now try to make your platforms move

[Hangedman]

Now try to make your platforms move