SDL C++ Time based movements

This is a discussion on SDL C++ Time based movements within the Game Programming forums, part of the General Programming Boards category; Hello Folks! I try to build a little game with SDL. But i cant figure out one thing. I need ...

  1. #1
    The Programming Dutchman
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    Jan 2008
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    SDL C++ Time based movements

    Hello Folks!

    I try to build a little game with SDL. But i cant figure out one thing. I need to make time based movements so the game would run on the same speed at all different types of PCs , I started looking on google at time based movements but all the examples where a little confusing for me. So my question is: you know know how to make time based movements with SDL?

    OS: Linux.
    Language: C++


    Thanks in advance.
    The Programming Dutchman

  2. #2
    Super Moderator VirtualAce's Avatar
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    Compute the time delta between the last frame and the current one. Use that time delta in all movement calculations.

    Note also that any constant speed values must be adjusted as well. So if you want to move 50.0f units at 16.66667 ms per frame and you are getting 32.66667 ms per frame you will need to adjust the value accordingly.
    Last edited by VirtualAce; 06-12-2010 at 09:52 AM.

  3. #3
    The Programming Dutchman
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    Wow, uhmm maybe i don't get it because my english not so good, but what is delta time?

    if you want to, could you provide a a little example code?

    sorry..... :$

    btw: thanks for you fast reply!

    Jelte.
    The Programming Dutchman

  4. #4
    System Novice siavoshkc's Avatar
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    Delta means difference:
    Code:
    delta(t) = t2 - t1
    Generally when you want your program to be CPU speed independent you need to make sure all your operations execute in a specific amount of time.
    Code:
    while()
    {
    ...
    if (GetCurrentTime() - tLastExecution >= tINTERVAL)
    {
    //do something example: move characters
    tLastExecution = GetCurrentTime();
    }
    [edit]
    //other operations can be performed with a ratio to main interval amount
    if (GetCurrentTime() - tBeeMovementLastExecution >=( tINTERVAL/4))
    {
    //do something example: move bee
    tBeeMovementLastExecution = GetCurrentTime();
    }
    }
    Last edited by siavoshkc; 06-12-2010 at 10:52 AM.
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  5. #5
    Registered User
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    This is a good tutorial about the subject: Fix Your Timestep! Gaffer on Games

  6. #6
    The Programming Dutchman
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    Thanks! that would solve my problem!

    Jelte.
    The Programming Dutchman

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