How to check if actor is in contact with a block/actor group?

[illyabusigin]

Hi John! I'm resuming work on my platformer and am trying to figure out the best way of determining if a user is in contact with a block/actor in a group.

My use-case is I have my player who will walk off the edge of an obstacle. When he walks off the edge I want to get a notification that he's no longer in contact with the ground so that I can apply gravity.

See GIF for my current behavior:

I've accomplished this by adding the following methods to Actor:

public func isInContact(withBlockGroup group: Group) -> Bool {
        for block in blocksInContact {
            if block.group == group {
                return true
            }
        }
        
        return false
    }
    
    public func isInContact(withActorGroup group: Group) -> Bool {
        for actor in actorsInContact {
            if actor.group == group {
                return true
            }
        }
        
        return false
    }

I have a plugin that watches for rectChanges and flips a flag which changes gravity behavior:

actor.events.rectChanged.addObserver(self) { (scene, player, stuff) in
            if !player.isInContact(withBlockGroup: self.floorGroup) {
                if self.isGrounded {
                    self.isGrounded = false
                }
            }
        }

Is there a better/more efficient way of doing this? If not I'd be happy to open a PR with the change.

[VNystad]

The way i've done this kind of collisiondetection is with a "2d"array, int[][]. It is done in c++, but i think it's somehow the same.

The size of 1 index in the array is 32*32 pixels, so the array coords for (24, 21) = [0][0] and (43,24) = [0][1]
I check if the array position below me has an value > 0 (a tile ID), if so, collision!
collidableArray[(int)(player.GetPosY()/ 32) + 1] [(int)player.GetPostX()/ 32] > 0, accessing array index O(1), so it's a really fast checkup

bool Physics::Grounded(Player* p, int** collidableArray)
{
// Variables for debugging
int playerArrayCoordX = (p->GetPosX() + 17) / 32;
int playerSouthCoord = ((p->GetPosY() + p->GetSizeHeight() / 2) / 32)>0 ? (p->GetPosY() + 50) / 32 : 0;
if (collidableArray[playerSouthCoord][playerArrayCoordX] > 0)
return true;
return false;
}