! 3D Animated Balls

gr.open 255,0,0,0

gr.orientation 0

gr.color 255,0,0,0

LET scw = 1280
LET sch = 800
LET csw = scw/2  % center_screenwidth
LET csh = sch/2  % center_screenheight

! 27 balls with 3 coordinates (x,y,z)
DIM balls [27,3]

lop: 

Gosub Rotate
Gosub sort_z
Gosub draw
GOTO lop

Rotate:

! increment = faster rotations
LET a = a + 0.1
LET b = b + 0.1
LET c = c + 0.1

LET i = 0

FOR x = -1 TO 1 
  FOR y = -1 TO  1 
    FOR z = -1 TO 1 
     LET i = i + 1

      ! rotate about the z-axis
     LET x1 = x*COS(a) - y*SIN(a)   
     LET y1 = y*COS(a) + x*SIN(a)   

      ! rotate about the y-axis
     LET x2 = x1*COS(b) - z *SIN(b) 
     LET z1 = z *COS(b) + x1*SIN(b)

      ! rotate about the x-axis
     LET y2 = y1*COS(c) - z1*SIN(c)
     LET z2 = z1*COS(c) + y1*SIN(c) 

      ! load array with rot. coordinates
      balls[i,1] = x2
      balls[i,2] = y2
      balls[i,3] = z2
    NEXT z
  NEXT y
NEXT x

LET i = 0

Return

sort_z:

! bubble sort z coordinate
FOR n = 27 TO 1 STEP -1
  FOR i = 1 TO n-1
    IF balls[i,3] > balls[i+1,3] THEN
      temp = balls[i,3]
      balls[i,3] = balls[i+1,3]
      balls[i+1,3] = temp  
      
      temp = balls[i,2]
      balls[i,2] = balls[i+1,2]
      balls[i+1,2] = temp

      temp = balls[i,1]
      balls[i,1] = balls[i+1,1]
      balls[i+1,1] = temp
    Endif
  NEXT i
NEXT n

Return

draw:

FOR i = 1 TO 27
  ! perspective trans. mod 500 value for depth
  LET sx = 500*balls[i,1]/(balls[i,3]-8)+csw
  LET sy = 500*balls[i,2]/(balls[i,3]-8)+csh

  ! green, darker if further away (z)
  gr.color 255,0,(balls[i,3]+2)*20,0
    
  ! circle, smaler if further away (z)
  gr.circle kr,sx, sy, (balls[i,3] + 4) * 6
NEXT i 

gr.render

gr.cls

Return