How do I make a sprite change size (or do other things) in a specific amount of time?

Cheezzychiknzzz

Suppose I want to make a sprite start at 100%, then shrink it smoothly to 80% in 2 seconds, and then I want it grow back smoothly to 100% in 2 seconds (again) and repeat the cycle forever. Plus, how do I apply it to other similar properties such as direction, graphic effects, etc…?

ajsya

I would just create some kind of loop that made it work out so that the sprite changed by the right size in the right amount of time.

when green flag clicked
forever
repeat (20)
change size by (-1)
wait (.1) secs
end
repeat (20)
change size by (1)
wait (.1) secs
end
end

I was going to try creating a custom block that did the changing size part, but I ran out of time. I think the timing is also a little messed up for some Scratch technical reason. It takes over 2 seconds to change the size even though it should only take 2 seconds theoretically since .1*20 is 2. I tried playing around with “run without screen refresh” and turbo mode, but it wasn't working for me.

dem_bot

You're probably looking for a sine wave. A sine wave usually goes from -1 to 1, so we have to multiply it by 10 to go from -10 to 10. Then we add 90 to it to go from 80 to 100.

((([sin v] of (t)::operators) * [10]) + [90])

t should constantly increase. Usually I would use the days since 2000 for this:

((days since 2000) * [big number just try some stuff out til u have a nice speed])

Edit: i just realised u want it to loop in 4 seconds.
In that case, the really big number is 360/4 * 3600 * 24

Last edited by dem_bot (Yesterday 16:59:25)

ajsya

dem_bot wrote:
You're probably looking for a sine wave. A sine wave usually goes from -1 to 1, so we have to multiply it by 10 to go from -10 to 10. Then we add 90 to it to go from 80 to 100.
((([sin v] of (t)::operators) * [10]) + [90])
t should constantly increase. Usually I would use the days since 2000 for this:
((days since 2000) * [big number just try some stuff out til u have a nice speed])
Edit: i just realised u want it to loop in 4 seconds.
In that case, the really big number is 360/4 * 3600 * 24

Smart! This is way better than what I came up with.

Woodfur

ajsya wrote:
I think the timing is also a little messed up for some Scratch technical reason. It takes over 2 seconds to change the size even though it should only take 2 seconds theoretically since .1*20 is 2. I tried playing around with “run without screen refresh” and turbo mode, but it wasn't working for me.

Loop blocks always add a 1/30th-second wait at the end. That's the frame rate Scratch projects run at, so it's better to work with it than against it.

forever
repeat (60) //number of frames in 2 secs
change size by ((1) / (3))
end
repeat (60)
change size by ((-1) / (3))
end

Run without screen refresh will cancel the delay, but it's meant for calculations that happen instantaneously—using it on actions that take measurable time can break your project.

Cheezzychiknzzz

But what if I want it to grow or shrink in a fractional number of time?

dem_bot

Cheezzychiknzzz wrote:
But what if I want it to grow or shrink in a fractional number of time?

with the sine wave you can basically do whatever as long as it fits in a double (the variable type scratch uses for numbers).
31104000/amount of seconds per rotation

kemlevor

when green flag clicked
set [caracteristic time v] to [2]
set [time v] to [0]
set [t0 v] to [150]
set [tf v] to [100]
set [step v] to [0]
forever
if <(step) = [0]> then 
change [time v] by (timer)
if <(time) > (caracteristic time)> then
set [time v] to (caracteristic time)
end  
set size to ((t0) + (((tf) - (t0)) * (( ([e^ v] of (((5) * (time)) / (caracteristic time))::operators) - (1)) / (([e^ v] of (5)::operators) - (1))))) %
if <(time) > (caracteristic time)> then
set [time v] to [0]
set [step v] to [1]
end
else
change [time v] by (timer)
if <(time) > (caracteristic time)> then
set [time v] to (caracteristic time)
end  
set size to ((tf) + (((t0) - (tf)) * (( ([e^ v] of (((1) * (time)) / (caracteristic time))::operators) - (1)) / (([e^ v] of (1)::operators) - (1))))) %
if <(time) > (caracteristic time)> then
set [time v] to [0]
set [step v] to [0]
end

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