Timer Based Movement - Frame Rate Independent Motion Example

[kevin]

  Timer Based Movement - Frame Rate Independent Motion Example


  This PlayBASIC code snippet shows how to make moving objects (balls) in a game move independently of the frame rate, meaning the movement looks consistent regardless of how fast or slow the game runs. This is achieved by using timers to calculate the position of each ball based on elapsed time rather than relying on the game's frame rate.

How It Works:

1. Setting Frame Rate Goals:

  - The program sets a target frame rate of 50 frames per second (FPS) and calculates how many milliseconds each frame should last (`1000 / 50 = 20ms` per frame).

2. Ball Setup:

  - The balls are defined using a custom type (`tBALL`) which includes properties like position (`X`, `Y`), size, color, speed, direction, and the time when the ball was created.

3. Adding Balls:

  - Balls are randomly generated within the display area with random sizes, colors, speeds, and directions. New balls are added every 50 milliseconds, creating a dynamic scene.

4. Moving the Balls:
  - The balls' positions are updated based on how much time has passed since each ball was created. This is calculated using the elapsed time and the ball's speed. The movement calculations are independent of the frame rate, making the motion consistent.

5. Rendering and Removal:
  - Each ball is drawn on the screen at its updated position. If a ball moves outside the display area, it's removed from the scene.

6. Display Information:
  - The program shows the current number of balls and the actual frames per second (FPS) at the top of the screen.

This approach ensures that the motion of the balls remains smooth and consistent, even if the game's performance varies. It's a great demonstration of using time-based calculations for movement, which is a valuable technique in game development to maintain consistency across different devices and frame rates.

PlayBASIC Code: [Select]

    // Ste our ideal  Required frames per second rate
    Frame_RATE# = 50

    // Ticks per frame
    Frame_RATE_MILLISECOND_PER_FRAME# = 1000.0/Frame_RATE# 
    

    Type tBALL
            X#
            Y#
            Size
            Colour
            Speed#
            Direction#
            StartTime
    EndType

    Dim Ball as TBall List
    
    CurrentTime = timer()

    Do
        
        Cls
        
        CurrentTime= Timer()

        //  Randomly Add more balls to the scene
        if Add_Balls < CurrentTime
        
            for lp =1 to rndrange(100,500)
                Ball                = new tBall
                Ball.x            = rndrange(100,GetsurfaceWidth()-100)
                Ball.y            = rndrange(100,GetsurfaceHeight()-100)
                Ball.size        = rndrange(10,20)
                Ball.Colour    = rndrgb()
                Ball.Speed        = rndrange#(1, 5)
                Ball.Direction    = rnd#(360)
                Ball.StartTime = CurrentTime
            next
            Add_Balls=CurrentTime+50    
        endif
        
        //  Draw Balls
        lockbuffer
        For each Ball()
            
            // How long as this ball been alive and move in this direction?
            ElapsedTime = CurrentTime-Ball.StartTime

            // compute how far this ball have moved since creation
            Dist#= (Ball.Speed /Frame_RATE_MILLISECOND_PER_FRAME#) * ElapsedTime

            //  Compute the moved position from it's origin point
            x#=Ball.x+cos(ball.direction)*Dist#
            y#=Ball.y+sin(ball.direction)*Dist#


            // check if the ball is on screen or not ? 
            // if not; delete it from the list 
            if x#<(-ball.size) or x#>(getSurfaceWidth()+ball.size) or              y#<(-ball.size) or y#>(getSurfaceHeight()+ball.size)
                    Ball=null
                    continue
            endif

            // draw the ball since it's still visible
            circlec x#,Y#,ball.size,true,ball.colour

        Next
        unlockbuffer
                    
        text 10,10,"Balls #"+str$(GetListSize(Ball()))
        text 10,20,"  Fps #" +str$(fps())
            
        sync
    
    Loop spacekey()

 

[kevin]

  I little effect for something fun to look at :)


Source Code Bellow: Just Some Circles

PlayBASIC Code: [Select]

    Screen=NewImage(getSurfaceWidth(),GetSurfaceHeight(),2)

    // Ste our ideal  Required frames per second rate
    Frame_RATE# = 50

    // Ticks per frame
    Frame_RATE_MILLISECOND_PER_FRAME# = 1000.0/Frame_RATE# 
    

    Type tBALL
            X#
            Y#
            Size
            Colour
            Speed#
            Direction#
            StartTime
                Mode
    EndType



    Dim Ball as TBall List
    
    Dim Modes(1)
    Modes(0)= 1+64
    Modes(1)= 1+128

    CurrentTime = timer()

    Do
        
        
        CurrentTime= Timer()

        //  Randomly Add more balls to the scene
        if Add_Balls < CurrentTime
        
            for lp =1 to rndrange(50,250)
                Ball              = new tBall
                Ball.x          = (GetsurfaceWidth()/2)-rnd(30)
                Ball.y          = (GetsurfaceHeight()/2)-rnd(30)
                Ball.size          = rndrange(10,100)
                Ball.Colour        = rndrgb() and $0f0f0f
                Ball.Speed      = rndrange#(1, 5)
                Ball.Direction  = rnd#(360)
                Ball.StartTime    = CurrentTime
                Ball.Mode            = Modes(lp&1)
            next
            Add_Balls=CurrentTime+50    
        endif
        
        
        rendertoimage screen
        Cls
        inkmode 1+64
        //  Draw Balls
        lockbuffer
        For each Ball()
            
            // How long as this ball been alive and move in this direction?
            ElapsedTime = CurrentTime-Ball.StartTime

            // compute how far this ball have moved since creation
            Dist#= (Ball.Speed /Frame_RATE_MILLISECOND_PER_FRAME#) * ElapsedTime

            //  Compute the moved position from it's origin point
            x#=Ball.x+cos(ball.direction)*Dist#
            y#=Ball.y+sin(ball.direction)*Dist#


            // check if the ball is on screen or not ? 
            // if not; delete it from the list 
            if x#<(-ball.size) or x#>(getSurfaceWidth()+ball.size) or              y#<(-ball.size) or y#>(getSurfaceHeight()+ball.size)
                    Ball=null
                    continue
            endif

                Inkmode Ball.Mode

            // draw the ball since it's still visible
            circlec x#,Y#,ball.size,true,ball.colour

        Next
        unlockbuffer


        rendertoscreen
        drawimage Screen,0,0,false
                    
        sync
    
    Loop spacekey()