2d Stars Example

[kevin]

2D Stars Examples


  This is classic 2D (right to left) star scrolling routine.  This version is using parallel arrays for the stars coordinate and speed. There's a bunch of ways to do this; but here we're create filling our star with a random starting coordinate within the bitmap screen as well as give this star a random speed.

  This is integer only so it has fixed point precision, which just means we scale our values up by some fixed constant and anything bellow this becomes the fractional part and anything above it is the whole number part. 

 

PlayBASIC Code: [Select]

; PROJECT : Project1
; AUTHOR  : 
; CREATED : 29/08/2023
; ---------------------------------------------------------------------

    AccBits = 2^16

    ScreenWidth =800
    ScreenHeight =600
    Count=25000

    Dim StarsX(Count)
    Dim StarsY(Count)
    Dim StarsSpeed(Count)

    For lp =0 to count
        StarsX(lp) = rnd(ScreenWidth*AccBits)
        StarsY(lp) = rnd(ScreenHEight-1)
        StarsSpeed(lp) = rndrange(1*AccBits,5*AccBits)
    next
        
    // -------------------------------------------
    do // Main Loop
    // -------------------------------------------

        cls

        lockbuffer    
            For lp =0 to count
            // Move the star to the left
            x=StarsX(lp)-StarsSpeed(lp)
            
            if X<0
                // wrap the X coordinate
                X=X+(ScreenWidth*AccBits)
                // give this star a new Y and speed
                StarsY(lp) = rnd(ScreenHEight-1)
                StarsSpeed(lp) = rndrange(1*AccBits,5*AccBits)
            endif
            // Store the updated X
            StarsX(lp)=x
            // draw it to the surface
            dot x/AccBits,StarsY(lp)
        next
        unlockbuffer    

        // flip the buffers
        sync
    loop spacekey()=true

 
   
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