How to create gravity in Scratch?

Question

For people looking to advance their skills in Scratch and add gravity and jumping to your 2D game. Simple to use and easily optimizable. This can work for platformers or other fun-skilled games.

Answer 1

To emulate the effect on scratch, we would start by creating a gravity variable. Make sure you are viewing the code of the sprite you wish to apply the effect to.

Step 1: Create a new variable called Gravity.

Step 2: Change the Gravity

You are going to want the gravity to slowly speed up while your player or other object is not touching the ground, color, or other collision detected object. You can do this by creating this script.

When Flag is Clicked:
     Forever:
        If(not touching[object or color]):
             Change(gravity) by -1
        If(touching[object or color]):
            Set(gravity) to 0

This will allow the gravity to slowly increase when the player is not colliding with the desired object. Now, you can apply this gravity by changing the y position of the player by gravity.

Full script:

When Flag is Clicked:
     Forever:
        If(not touching[object or color]):
             Change(gravity) by -1
             end
        If(touching[object or color]):
            Set(gravity) to 0
            end
        Change Y By(gravity)

Extra: If you want to take it to another level, you are able to add a jump effect. It is quite easy.

Script:

When Flag is Clicked:
    Forever:
       If(touching[object or color] and [key(up) is pressed]):
           Set(gravity) to (desired jump height value)

Answer 2

Uhm, so assuming there are walls and ceilings in your platformer

First, you need the following variables

X_Vel (X's velocity)

Y_Vel (Y's velocity)

Alongside the X and Y of the player

And then assuming that the ground is a sprite called Level

Then you can make this for gravity

Y_Vel = Y_Vel - 1
Y = Y + Y_Vel

And then for floor collision

if (Touching Level) then
    Ground <- Custom block
    
    if (Space Pressed) then
        Y_Vel = 10 <- For jumping
    else
        Y_Vel = 0 <- Player doesn't melt to the floor
    end
end

And then for the custom "Ground" block

Define Ground
    repeat (abs(Y_Vel))
        if (Touching Level) then
            Y = Y + ((abs(Y_Vel) / Y_Vel) * -1)
        end
    end
end

You might notice that the character won't actually go all the way back up if it doesn't hit the ground hard enough, and that's intentional and needed for wall collisions

You might also notice that the character might also go downwards too if Y_Vel is positive, which is also intentional and needed for ceiling collision

Moving on, we're going into the left and right code since we haven't finished the wall collision code, and because you said platformers. We're going to need velocity to move the player for the wall collisions so this is what goes next:

if (A Pressed) then <- Or Right arrow key
    X_Vel = -10
end

if (D pressed) then <- Or Left arrow key
    X_Vel = 10
end

X = X + X_Vel <- Move player

Feel free to edit the code above for more features like sprinting, acceleration, rolling, etc.

And then finally, wall collision

if (Touching Level) then
    X = X + (X_Vel * -1)
    X_Vel = 0
end

That's it... Unless you want to improve the wall collision and mimick the ground/ ceiling collision. Well, here you go!

Of course, it'd be much better if you just watch a YouTube tutorial on this problem.