From Test-Scratch-Wiki
There are many ways to jump depending on how you want a sprite to jump. This article contains a number of them, categorized from least-realistic to most realistic. The ↑ key is usually used for jumping in games, but sometimes Space, Z,X,W, or even the mouse is used for jumping.
Simple jumping
The following is commonly used in animations and results in a sprite effectively teleporting upwards, and then downwards again.
when green flag clicked
forever
if <key [up arrow v] pressed?> then //typical jumping key
change y by (50)
wait (0.5) secs
change y by (-50)
end
The below script results in the sprite moving up if the up arrow is pressed.
when green flag clicked
forever
if <key [up arrow v] pressed?> then //typical jumping key
change y by (5)
end
It was used in the Scrolling Demo project by SampleProjectsTeam.
Falling
The following script "teleports" the sprite upwards, and then has it fall back down at a constant rate, until it lands on a platform.
when green flag clicked
forever
if <key [up arrow v] pressed?> then //typical jumping key
change y by (50)
repeat until <touching color [#000000]?> //color of the ground
change y by (-5)
end
end
end
The next script makes the sprite rise up at a constant rate and fall back down at a constant rate.
when gf clicked forever if <key [up arrow v] pressed?> then //typical jumping key repeat (10) change y by (5) end repeat until <touching color [#000000]?> //color of the ground change y by (-5) end end
Limited Jumps
In most video games, you cannot jump more than a certain number of times, and you cannot jump in midair. This can be implemented in Scratch.
The purple blocks labeled "jump" represent a compatible jump script.
To allow you to only jump on the ground, use the following script.
when gf clicked forever if <<key [up arrow v] pressed?> and <touching color [#000000]>> then // typical jumping key, color of the ground change y by (5) jump // category=custom end
Double jumping is a common element in video games. Although not possible in real life, these scripts can make you jump up to two times.
when gf clicked forever if <touching color [#000000]?> then // color of the ground set [jumps v] to [0] end when gf clicked forever if <<key [up arrow v] pressed?> and <touching color [#000000]>> then // typical jumping key change y by (5) // this will keep the first script for resetting the jump count change [jumps v] by (1) jump // category=custom else if <<key [up arrow v] pressed?> and <(jumps) < [2]>> then // This will keep you from jumping more than twice change [jumps v] by (1) jump // category=custom end end
To make the sprite jump up to n times, change the 2 to an n.
Physically Accurate Jumping
With Ground Detection
A more realistic effect for jumping commonly used in games is the following, using a variable to control the vertical speed of a sprite (simulating gravity) is this:
when green flag clicked
set [y speed v] to [0]
forever
change y by (y speed)
when green flag clicked
forever
if <<key [up arrow v] pressed?> and <(y speed) = [0]>> then //typical jumping key
set [y speed v] to (9.9)
repeat until <touching color [#000000]?> //the color of the platforms
change y by (y speed)
change [y speed v] by (-0.5)
end
set [y speed v] to (0)
end
Without Ground Detection
If one does not need to sense the ground and simply want a realistic, gravitational jump, that will end at the starting point, the following script can replicate the jump:
when gf clicked forever if <key [up arrow v] pressed?> then set [y vel v] to (10) repeat (20) change y by (y vel) change [y vel v] by (-1) //simulates gravity end end
Advanced Jumping
The following script includes velocity-based jumping and advanced landing. The sprite is constantly acted upon by the force of gravity and cannot pass through sprites. The sprite may appear to "bounce" slightly when "at rest":
when gf clicked forever change [yvel v] by (-0.2) // simulates the force of gravity change y by (yvel) if <touching [platforms v]?> then// if the sprite hits an object set [yvel v] to ((-0.34)*(yvel)) // bounce off of it change y by (yvel) if <touching [platforms v]?> then change y by (yvel) if <touching [platforms v]?> then change y by (yvel) end end if <<(yvel) > (0)>and<key [up arrow v] pressed?>> then// jumping script set [yvel v] to (4) // jump magnitude (a higher number results in a higher jump) end
In the above script, gravity was added to create a realistic effect; you can read more about simulating gravity here.
