A time acceleration function
Posted: 02.05.2004, 01:46
Hello,
Let's suppose that in your script you need to compress X days into Y seconds. Then you convert these X days to seconds and divide this by Y seconds, obtaining a time factor F, that you can use to increase time speed.
But this "acceleration" is really a jump from 1 to F in zero time, and produces a not so pleasant effect.
The function below, instead, applies a smooth acceleration to time, assuring a much better result (that may be very suitable for certain visual purposes)
The script also includes two use examples.
Please post suggestions and bugs here.
Bye
Let's suppose that in your script you need to compress X days into Y seconds. Then you convert these X days to seconds and divide this by Y seconds, obtaining a time factor F, that you can use to increase time speed.
But this "acceleration" is really a jump from 1 to F in zero time, and produces a not so pleasant effect.
The function below, instead, applies a smooth acceleration to time, assuring a much better result (that may be very suitable for certain visual purposes)
The script also includes two use examples.
Code: Select all
--*********************************************************
--*********************************************************
-- accTime()
-- A function to calculate smooth time acceleration
--
-- coded by Toti
--*********************************************************
--*********************************************************
--****************************************************
-- constants (only used by the main program)
--****************************************************
DELAY = 5
--****************************************************
-- the accTime() function
--
-- parameters:
-- DT: real time interval in days
-- dt: simulation time interval in seconds
-- (where DT will be compressed into)
--****************************************************
function accTime (DT, dt)
local st0 = celestia:getscripttime()
local pi = math.pi
local k = ((DT/dt * 43200) - 0.5) * pi -- 43200 * 2 = seconds in a day
local period = pi / dt
local dst = 0 -- without this, 'repeat-until' does not work
repeat
wait()
dst = celestia:getscripttime() - st0
local ts = k * math.sin (dst * period) + 1
celestia:settimescale (ts)
-- you can comment this line:
celestia:flash (string.format("Seconds: %3.0f" , dst), DELAY)
until dst >= dt
celestia:settimescale (1) -- correct floating point error
end
--****************************************************
-- use the function
--****************************************************
upVector = celestia:newvector(0,1,0)
obs = celestia:getobserver()
earth = celestia:find("Sol/Earth")
celestia:select(earth)
obs:gotolonglat(earth, 0, 0, 20000, DELAY)
obs:lookat(earth:getposition(),upVector)
celestia:flash ("Let's show an entire Earth day in ten seconds...", DELAY)
wait(DELAY)
--**************************
--Here is the function call
--**************************
accTime (1, 10)
celestia:flash ("And now...", DELAY)
wait(DELAY)
sol = celestia:find("Sol")
obs:gotolonglat(sol, 0, 1.5707, 4*1e8, DELAY)
obs:lookat(sol:getposition(),upVector)
wait(DELAY)
-- be sure to show planet's orbits and flags
oldrf = celestia:getrenderflags()
oldlf = celestia:getlabelflags()
oldof = celestia:getorbitflags()
celestia:setrenderflags{constellations=false,eclipseshadows=true,galaxies=true,grid=false,lightdelay=false,markers=false,
nightmaps=true,orbits=true,planets=true,ringshadows=true,smoothlines=false,stars=true}
celestia:setlabelflags{asteroids=false,spacecraft=false,comets=false,constellations=false,locations=false,moons=false,
planets=true,star=false}
celestia:setorbitflags{Planet=true,Moon=false,Comet=false,Asteroid=false,Spacecraft=false}
celestia:flash ("...let's watch ten Earth years in twenty seconds...", DELAY)
wait(DELAY)
--**************************
--Here is the function call
--**************************
accTime (365*10, 20)
celestia:flash ("That was all!", DELAY)
wait(DELAY)
-- restore user's defaults
celestia:setrenderflags(oldrf)
celestia:setlabelflags(oldlf)
celestia:setorbitflags(oldof)
Please post suggestions and bugs here.
Bye
