So essentially you've just got negative acceleration, so we'll use the formula
d = 1/2*a*t*tsolved for a (acceleration):
JASS:
d = 1/2*a*t*t
2*d = a*t*t
a = 2*d/(t*t)
So in your example you have the duration (t) 4.00 seconds, the timer callback probably runs every 0.03 seconds, and a distance (d) of 1000.00 units. Thus, your acceleration is calculated as
a = 2*1000.00/(4.00*4.00), or
a = 125.00 units/second. Then, we need to divide by 33.33 (since that's roughly how many times 0.03 goes into 1.00) to get the acceleration per timer interval which would be, in this case,
3.7504.
Last, you need to get your initial speed. Since linear acceleration is just (Final Speed-Initial Speed)/Time, you simply multiply the acceleration/TimerInterval by the total time (4.00 seconds) to get the initial velocity in units/TimerInterval. Thus, it would be 15.0002.
Of course, you then multiply the acceleration by -1.00 such that the object slows down from a fast velocity to rest instead of the other way around.
So you'd do something like this:
JASS:
function Callback takes nothing returns nothing
local real X = HoweverYouGetX()
local real Y = HoweverYouGetY()
local real Acceleration = HoweverYouGetTheAcceleration()
local real Velocity = HoweverYouGetTheVelocity()+Acceleration
local real Angle
local unit U = HoweverYouGetTheUnit()
if Velocity > 0.00 then
set Angle = HoweverYouGetTheAngle()
call HoweverYouStoreReals(Velocity)
call SetUnitX(U, X+Velocity*Cos(Angle))
call SetUnitY(U, Y+Velocity*Sin(Angle))
else
call HoweverYouCleanUp()
endif
set U = null
endfunction
And of course storing the appropriate values at the initiation of the knockback.
