How do I stay on steep slopes with move_and_collide()?

[NorthernQuokka]

Godot Version

4.2.2

Question

I am currently replicating 2d sonic physics, and I am struggling to figure out how to stay on slopes with move_and_collide(). In the 2d Sonic games, the player would always stay on slopes unless they jumped, ran off a ramp, or ran too slow. My code works fine for concave slopes, but the player falls off convex slopes when they get too steep (about 45 deg). I would use move_and_slide() if I could, but it doesn’t work with a different part of my code. Is there any way I could make this work?

[tayacan]

Hard to say what’s going wrong without seeing some relevant snippets of code.

You might be interested in this paper about collision detection and sliding. It’s not engine-specific, and assumes no built-in collision handling, but you can probably look at the parts that deal with sliding and implement something like it on top of move_and_collide, if you want functionality like move_and_slide, but customized in some way.

[gertkeno]

Maybe you can use the last collided surface’s normal as a influence on direction

var floor_forward = last_collision.get_normal()
floor_forward = Vector2(floor_forward.y, -floor_forward.x) # turn 90 degrees right

velocity = floor_forward * input * speed

last_collision = move_and_collide(velocity * delta)

[NorthernQuokka]

I figured it out. I added two raycasts that extend below the player. Then I used them when my original two raycasts failed. If one of them was colliding while grounded, I set my grounded variable to true.

var collisionA = sensorA.is_colliding()
var collisionB = sensorB.is_colliding()
var collisionA1 = sensorA1.is_colliding()
var collisionB1 = sensorB1.is_colliding()

if collisionA or collisionB:
	grounded = true
elif collisionA1 or collisionB1:
	if !inAir:
		grounded = true
	else:
		grounded = false