Adding Leniency to Jumping Mechanic

Question

I have written some jumping code for my player in a platformer game. At the moment it has some basic logic which says that the player can jump if he is on the ground. The pseudocode looks something like this:

### Input Handling ###
if(jumpButtonPressed){
    if(onGround){
        jump
    }
}

### Player Update Loop ###
onGround = false
movePlayer
resolveCollisions
if(player collided with ground){
      onGround = true
}

This works fine for basic static tile levels, but when the player is standing on a descending platform, or moving down a downward slope for instance, it becomes very difficult to jump. The reason for this (in the case of the descending platform) is that the platform has moved from underneath him in that frame, so for that moment he is not actually colliding with the ground, and therefore the condition to be able to jump is not fulfilled.

Is there a general way to add some leniency into the jump mechanic so that the player can jump even if they are not technically on the ground for that exact frame? This seems like it should be quite a common problem but I cannot seem to find any similar questions on stackexchange or google.

Answer 1

The best solution for this is largely going to be a product of tweaking and testing. If you've seen the documentary Indie Game, one of the designers/programmers of Super Meat Boy talks about all of the time he spent endlessly tweaking jumping and wall sliding, until it felt right.

There may not be a perfect solution, and moving platforms have long posed an issue for physics, but here is something you can try. Rather than using a boolean to keep track of whether you are touching the ground, try using a timer. Every time the player has a collision with the ground, reset the timer, and allow him to jump while the timer is non-zero. Jumping should kill the timer, obviously. The time should be very short, and it may allow characters to jump in the air just after running off a platform, which you may see as good or bad.

An alternative, depending on the implementation of gravity, is just tracking a frame count (like 2 or 3 frames). I don't like this as much because it's performance-dependent, but it could be that the character is actually standing on the descending platform only every-other frame, and this would resolve that. (collide & become still, then the platform drops and he has a collision-less fall).

You could, as a third solution, check to see how your physics deals with the character once he hits the platform. Namely, does it set his y-velocity to 0, or to the y-velocity of the object he had a collision with? If the answer is 0, adjusting that could be sufficient.