Tried to mod the Grandma Engine in order to add moving platforms to it so I can understand collisions better. However I got two issues.
For platforms moving horizontally, the player's friction gets eliminated the moment it lands on it.
For platforms moving vertically I also see a 1 pixel offset from time to time, especially when jumping on the platform while it is moving.
Finally the jumpthrough functionality is ruined.
Download gmz here.
A question I also have is,
What is the correct code for checking the player's bottom position of the bounding box against the bounding box top of other object? e.g. A player checking that there is floor below him.
Why place_meeting(x, y+1, obj_floor) does not always work? Especially when falling on a floor that moves upwards, it will fail most of the times.
This also often fails as well collision_rectangle(bbox_left, bbox_bottom+1, bbox_right, bbox_bottom+1, obj_wall, 1, 1);