Timer-based movement problem - GameCreators Forum

Author

Message

gUESS

17

Years of Service

User Offline

Joined: 18th Feb 2008

Location: Looking for my mind. Have you seen it?

Posted: 18th Feb 2008 08:48

Link

Hi,

I have got timer based movement working alright but the way I have it implemented I don't see how i can apply it to this situation.

I currently have it where it is just a variable that controls how much I increment or decrement certain values like this:

+ Code Snippet

rem Move the object based on sync rate
position = position + (movement * timerValue)

What I need is for it to apply to something similar to applying friction where I multiply a value every loop like this:

+ Code Snippet

rem A little friction applied every loop
movement = movement * 0.98

The only way I can see doing this is to check it with a timer every loop to see if a certain amount of time has passed before executing this statement.

Any help?

Back to top

Profile PM

Libervurto

18

Years of Service

User Offline

Joined: 30th Jun 2006

Location: On Toast

Posted: 18th Feb 2008 12:32

Link

What would you use time based movement for?

Back to top

Profile PM Email

gUESS

17

Years of Service

User Offline

Joined: 18th Feb 2008

Location: Looking for my mind. Have you seen it?

Posted: 18th Feb 2008 23:13

Link

I don't quite get what you mean but basically I want to have everything moving consistently no matter what the frame rate.

What I'm am trying to apply this to is something like curvevalue() which I use to simulate friction when ever I'm doing physics stuff. I do got something like a workaround where I just this calculation every set amount of milliseconds. The problem with this is that it can get out of sync if the framerate is low enough.

Back to top

Profile PM

Ortu

DBPro Master

17

Years of Service

User Offline

Joined: 21st Nov 2007

Location: Austin, TX

Posted: 19th Feb 2008 06:13

Link

the friction (or any speed adjustment) should be applied to the movement increment in a single formula. something like:

position=newvalue(position,direction,(speed*time elapsed since last check*friction)

speed=distance/time to cover distance i.e. 1unit per 50ms speed#=1.0/50.0

Back to top

Profile PM Email Website

Latch

18

Years of Service

User Offline

Joined: 23rd Jul 2006

Location:

Posted: 19th Feb 2008 06:43

Link

@guess

One thing you can do is program your game or physics demo to run at a certain FPS on your machine. You then create an adjustment variable that represents a percentage of your desired fps to the actual fps. Use this percentage to apply to positioning, rotation, etc of your objects. This will keep everything moving and rotating at relative distances but will be smoother the closer the actual fps is to your desired fps and more choppy the slower the actual fps is. Because it is a percentage, the movements should be pretty much the same visually.

In the following 2 examples, I have a cube that is supposed to rotate 2 units per refresh. I want the sync rate to be 60 FPS ideally. In example one, everything is fine, and the factor (adjment#) ends up being a little less than 1 because the actual fps runs at about 62. So the speed of rotation is 1.9something units per refresh.

+ Code Snippet

srate#=60
sync on
sync rate srate#
autocam off

make object cube 1,25

position camera 0,0,-60
sync

for n=1 to 100
   rem bring fps up to whereever it will be
   sync
next n

do
   fps#=screen fps()*1.0
   if fps#=0 then fps#=1
   adjment#=srate#/fps#

   speed#=2*adjment#

   turn object left 1,speed#

   text 0,0,"Speed adjustment factor = "+str$(adjment#)
   text 0,20,"Actual FPS = "+str$(fps#)
   text 0,40,"Cube Rotation Speed "+str$(speed#)

   sync
loop

Now in example 2, I add about 1000 spheres just to eat up FPS. On my machine, the actual fps drops down to about 30 but the ideal is still 60 so the cube's rotation gets calculated at about 4 units per refresh. When running this example, give it a minute to create all of the spheres.

You'll notice that the rotation of the cube appears at about the same except it's just a little more jagged because it rotates a little faster to compensate for the reduction in fps:

+ Code Snippet

srate#=60
sync on
sync rate srate#
autocam off

make object cube 1,25

for obj=100 to 1000
   make object sphere obj,1
next obj

position camera 0,0,-60
sync

for n=1 to 100
   rem bring fps up to whereever it will be
   sync
next n

do
   fps#=screen fps()*1.0
   if fps#=0 then fps#=1
   adjment#=srate#/fps#

   speed#=2*adjment#

   turn object left 1,speed#

   text 0,0,"Speed adjustment factor = "+str$(adjment#)
   text 0,20,"Actual FPS = "+str$(fps#)
   text 0,40,"Cube Rotation Speed "+str$(speed#)

   sync
loop

If you use the adjustment# variables on all objects in terms of their speed and/or rotation, your game should run at the same speed on every machine. The higher the machine's fps, the smoother it will be. The lower, the more jagged it will be.

Enjoy your day.

Back to top

Profile PM

gUESS

17

Years of Service

User Offline

Joined: 18th Feb 2008

Location: Looking for my mind. Have you seen it?

Posted: 20th Feb 2008 01:07

Link

Latch,
I already have something like that implemented and it works fine. The problem though is when I try to use my adjment# with something like:

+ Code Snippet

velocity# = velocity# * friction#
position# = position# + velocity#

Using the timer value (adjment#) on this doesn't work properly in any way I see.

My question was if there was any way of getting this to work properly aside from doing something like this:

+ Code Snippet

rem Pseudo-Code
if timeElapsed > syncTime
   velocity# = velocity# * friction#
endif
position# = position# + velocity#

The snippet here will only work properly if the frame rate is high enough (e.i. Actual_Frames_Per_Second >= syncTime).

Back to top

Profile PM

jason p sage

17

Years of Service

User Offline

Joined: 10th Jun 2007

Location: Ellington, CT USA

Posted: 21st Feb 2008 22:59 Edited at: 28th Mar 2008 21:20

Link

First Off. Congrats! You're trying to go about it the Right Way.

Second - You should make a function that calls the CLOCK ONCE!

Third - The Timer Function Needs to Make Sure at least One Millisecond has passed before trying to change its "OLD TIME" and "NEW TIME" values. (Keeps math predictable.)
[edit]Ok.. Not Quite... Instead I think you should just set Time Elapsed to ZERO, BUT Keep your OLD TIME. When 1 or more milliseconds passes - THEN calc elapsed time from that. [/edit]

Forth - You should TRY to make Your Calc'd multipliers in One place (just for Organization - and partially for speed reasons as it prevents calc'ing stuff twice.

Ok...We In Dark Basic Classic? Hmm...

+ Code Snippet

` Init code - Prime the Pump
TimerNew=timer()
TimerOld=TimerNew-1
TimerElapsed=TimerNew-TimerOld ` Just Self Documenting :)

BallSpeedMult#= 0.1
BallSpeedCalc# = 0

...
do
  ' You Main Loop - first Call Timer Thingy
  gosub UpdateClock

  ...
  
  ` Do this to "PreCalc Your Time Stuff"
  BallSpeedCalc# = BallSpeedMult# * TimerElapsed

  `Then Apply it... That way the value is available 
  ` multiple times if  you need it... (multiply = slow math)
  move object 1, BallSpeedCalc#
loop until 1=2



UpdateClock:
  TempTime = Timer()
  if(TempTime <> TimerNew)
    TimerOld = TimerNew
    TimerNew = Timer()
    TimeElapsed = TimerNew - TimerOld
  else
    TimeElapsed = 0
  endif
return

[edit]Code Change[/edit]

Hope that is helpful

http://www.jasonpetersage.com/?PAGE=ironinfantry&SECTION=ironinfantry

Back to top

Profile PM Email Website

gUESS

17

Years of Service

User Offline

Joined: 18th Feb 2008

Location: Looking for my mind. Have you seen it?

Posted: 22nd Feb 2008 00:02

Link

Sorry if I might not be clear enough (or It might be me misunderstanding you guys) but I already have Timer-Movement working very well for normal movement. Its just that I don't really know how to apply it to something that works like a curvevalue. I have here an example program that might help.

sync on : sync rate 40
autocam off

rem This is the speed at which you want the object to move relative to the framerate
baseTime = 40
rem Set the current sync rate
fps = 40
rem Set the object starting position
x# = 500
z# = 500

gosub Setup

rem Set the timer variable for timer-based movement
synctimeInt = timer()

rem Main Loop
do
sync rate fps

rem Display Info
set cursor 0,0
print "Frame Rate: ";screen fps()
print "Sync Rate: ";fps
print "Rate at which the object will move: ";moveVar#
center text 320,0,"Use arrow keys to move ball"
center text 320,20,"Press control to change sync rate"

rem Control object movement
if upkey() = 1 then zvel# = zvel# + 0.1
if downkey() = 1 then zvel# = zvel# - 0.1
if rightkey() = 1 then xvel# = xvel# + 0.1
if leftkey() = 1 then xvel# = xvel# - 0.1

rem Press control to change to a different sync rate
if controlkey() = 1
   if hitKey = 0
      inc fps,20
      if fps > 40 then fps = 0
      hitKey = 1
   endif
else
   hitKey = 0
endif

rem ----------------------------------------------------------------------
rem This is how I calculate the physics
rem This is where I apply friction to gradually slow the object down
xvel# = xvel# * 0.98 :`<- How do you make this consistant no matter the frame rate?
zvel# = zvel# * 0.98

rem Here I update the object position
x# = x# + (xvel# * moveVar#) :`<- Here is where I make sure the object always moves at the same speed
z# = z# + (zvel# * moveVar#)
rem ----------------------------------------------------------------------

rem Keep te ball in bounds
if x# > 500 then x# = 500 : xvel# = xvel# * -1
if x# < 0 then x# = 0 : xvel# = xvel# * -1
if z# > 500 then z# = 500 : zvel# = zvel# * -1
if z# < 0 then z# = 0 : zvel# = zvel# * -1

rem Update Object
position object 1,x#,5,z#
rem Update camera
position camera 0,50,0
point camera x#,0,z#

sync
   rem Caclulate Timer-Based Movement
   loopTime# = (timer() - syncTime)
   if loopTime# > 0 then moveVar# = loopTime# / (1000 / baseTime) else moveVar# = 1
   rem Reset the timer variable
   syncTime = timer()
loop

rem Setup Scene and objects
Setup:

rem Make the object for an example
   make object sphere 1,10
   rem Make the scene
   make matrix 1,500,500,10,10

return

+ Code Snippet

sync on : sync rate 40
autocam off

rem This is the speed at which you want the object to move relative to the framerate
baseTime = 40
rem Set the current sync rate
fps = 40
rem Set the object starting position
x# = 500
z# = 500

gosub Setup


rem Set the timer variable for timer-based movement
synctimeInt = timer()

rem Main Loop
do
sync rate fps

rem Display Info
set cursor 0,0
print "Frame Rate: ";screen fps()
print "Sync Rate: ";fps
print "Rate at which the object will move: ";moveVar#
center text 320,0,"Use arrow keys to move ball"
center text 320,20,"Press control to change sync rate"


rem Control object movement
if upkey() = 1 then zvel# = zvel# + 0.1
if downkey() = 1 then zvel# = zvel# - 0.1
if rightkey() = 1 then xvel# = xvel# + 0.1
if leftkey() = 1 then xvel# = xvel# - 0.1



rem Press control to change to a different sync rate
if controlkey() = 1
   if hitKey = 0
      inc fps,20
      if fps > 40 then fps = 0
      hitKey = 1
   endif
else
   hitKey = 0
endif



rem ----------------------------------------------------------------------
rem This is how I calculate the physics
rem This is where I apply friction to gradually slow the object down
xvel# = xvel# * 0.98 :`<- How do you make this consistant no matter the frame rate?
zvel# = zvel# * 0.98

rem Here I update the object position
x# = x# + (xvel# * moveVar#) :`<- Here is where I make sure the object always moves at the same speed
z# = z# + (zvel# * moveVar#)
rem ----------------------------------------------------------------------


rem Keep te ball in bounds
if x# > 500 then x# = 500 : xvel# = xvel# * -1
if x# < 0 then x# = 0 : xvel# = xvel# * -1
if z# > 500 then z# = 500 : zvel# = zvel# * -1
if z# < 0 then z# = 0 : zvel# = zvel# * -1


rem Update Object
position object 1,x#,5,z#
rem Update camera
position camera 0,50,0
point camera x#,0,z#

sync
   rem Caclulate Timer-Based Movement
   loopTime# = (timer() - syncTime)
   if loopTime# > 0 then moveVar# = loopTime# / (1000 / baseTime) else moveVar# = 1
   rem Reset the timer variable
   syncTime = timer()
loop

rem Setup Scene and objects
Setup:

   rem Make the object for an example
   make object sphere 1,10
   rem Make the scene
   make matrix 1,500,500,10,10

return

Back to top

Profile PM

jason p sage

17

Years of Service

User Offline

Joined: 10th Jun 2007

Location: Ellington, CT USA

Posted: 22nd Feb 2008 00:26 Edited at: 22nd Feb 2008 00:27

Link

Ok - this isn't a double - post - there is a delay for the noob hahah

anyway - he said that ... Well.. My intpretation was - You misunderstood me GUYS - Timer movement isn't the Problem you idiots - Its I'm trying to do physics and get something like Curve Value!

LOL.... OH.... Yeah - Cool - I knew you were doing it right LOL

I ran into that - and I learned the importance of a "Heartbeat" in your game. If you make a heart beat - for your physics and stuff... you can USE Curve Value BECAUSE Heart beat you make your code only call at a specified (timer based) interval.... Like every tenth of a second.

Example - Physics engines sometimes use Herat beat" approach so TIME doesn't really effect the calculations because the time is a constant (usually.... enough where it doesnt matter)

Try it.

[edit] I hope people know I was joking and he didn't call anyone any names...he was most polite.[/edit]

http://www.jasonpetersage.com/?PAGE=ironinfantry&SECTION=ironinfantry

Back to top

Profile PM Email Website

gUESS

17

Years of Service

User Offline

Joined: 18th Feb 2008

Location: Looking for my mind. Have you seen it?

Posted: 23rd Feb 2008 06:56

Link

That heart-beat thing sound like the way to go and I have toyed with it before.

I was kind of hoping to use some calculation based on the timerMove-variable but oh well.

The only problem I see with the heart-beat, game tick thingy is that if the frame rate lasts longer then however long the tick is supposed to be, that part of your game will start to go out of sync. Though in retrospect if that does happen, the frame-rate will be unacceptable and that should be the main priority.

Anyways, thanks for helping me out.

@jason
One more thing, how were you able to see my post before it got approved?

Back to top

Profile PM

jason p sage

17

Years of Service

User Offline

Joined: 10th Jun 2007

Location: Ellington, CT USA

Posted: 23rd Feb 2008 15:11

Link

Email Notifications.

Either everyone get's em or I'm priveledged. I Doubt the latter.

One does need to click the "Recieive Email Notifications" when they post though to get email.

http://www.jasonpetersage.com/?PAGE=ironinfantry&SECTION=ironinfantry

Back to top

Profile PM Email Website

Latch

18

Years of Service

User Offline

Joined: 23rd Jul 2006

Location:

Posted: 23rd Feb 2008 18:23

Link

@gUESS
OK, now I get it. After going through multiple timer based methods, it's not the movement, it's the gradual reduction in speed that is the problem.

So, say the car moves at 10 units per refresh at 50 fps. That means in theory it would move at 5 units per refresh at 100 fps. But applying .98*10 versus .98*5 doesn't produce the same slow down.

So the formula becomes 10*.98 = 5 * x
x = 1.96
But this doesn't make sense because that would actually make the car speed up so we have to use a different method (not multiplication of the friction coefficient alone) perhaps to slow the car.

The factor has to be time. We have to have a longer period of time to slow the car down when it's moving at less units per refresh. So we need a motion equation that takes into account time,veolcity and instead of just friction, acceleration.

s=(iv*t)+(a*(t^2))/2
where
s=the distance the car will move
iv=the initial velocity of the car
a=the decceleration
t=the time interval

Enjoy your day.

Back to top

Profile PM

gUESS

17

Years of Service

User Offline

Joined: 18th Feb 2008

Location: Looking for my mind. Have you seen it?

Posted: 26th Feb 2008 23:30

Link

Latch,

I think I see somewhat how that is supposed to work but I tried it and am confused on a few things.

How do find the value for a (deceleration)?
Is it based on the current velocity like velocity * 0.98?
Could it be a constant instead (negative/positive).

Also, what exactly is t (time interval)?
Is it supposed to be something like moveVar# from the example I posted earlier?

Please explain.

Back to top

Profile PM

jason p sage

17

Years of Service

User Offline

Joined: 10th Jun 2007

Location: Ellington, CT USA

Posted: 27th Feb 2008 00:01

Link

I recently released Iron Infantry DBPro Demo + EXE + Source - and my Tanks and the Helicopters decelerate - and are based on timer movement. Seek it out (Or follow my sig) and view the source code - it might help....plus its fun to play.

http://www.jasonpetersage.com/?PAGE=ironinfantry&SECTION=ironinfantry

Back to top

Profile PM Email Website

Sorry your browser is not supported!

DarkBASIC Discussion / Timer-based movement problem