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Thread: Example: Section 8.3 (page 265), A little MORE Gravity! 2 Bodies

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    Example: Section 8.3 (page 265), A little MORE Gravity! 2 Bodies

    [code=thinbasic]
    ' Example: Section 8.3 (page 265), A little MORE Gravity! 2 Bodies

    ' From Stan Blank's Book:
    ' "Python Programming in OpenGL
    ' "A Graphical Approach to Programming

    ' Converted by Michael Clease (Stolen timing ideas from Petr..hehe)
    ' Last modified: February 27, 2010

    Uses "TBGL"

    ' Handle for our window
    Global hWnd As DWord
    Global Width As Long
    Global Height As Long
    Global vx1, vy1, vz1, x1, y1, z1, r2, r3, ax1, ay1, az1, dt As Double
    Global vx2, vy2, vz2, x2, y2, z2, ax2, ay2, az2, G As Double
    Global m1,m2, rad1 ,rad2 As Double

    Dim Title As String Value "A little MORE Gravity! 2 Bodies Simulation - 'Esc' to quit"
    width = 500
    height = 500
    '
    ' Create and show window
    hWnd = TBGL_CreateWindowEx(Title, Width, Height, 32, %TBGL_WS_WINDOWED )
    TBGL_ShowWindow

    Init()'Anim,x,y,dx,dy,axrng)
    ' Define "Callback" to be fired + that it should be fired each 10ms
    TBGL_BindPeriodicFunction(hWnd, "PlotFunc", 10)

    ' -- Once the command below is executed, further script execution
    ' -- is halted and only periodic calling of the bound function is performed
    TBGL_ProcessPeriodicFunction(hWnd)

    TBGL_DestroyWindow

    Sub Init()
    '# initial x,y,z positions For both stars
    x1 = 1.0
    y1 = 0.0
    z1 = 0.0
    x2 = -1.0
    y2 = 0.0
    z2 = 0.0
    '# initial vx,vy,vz velocities For both stars
    vx1 = 0.0
    vy1 = -0.128571428
    vz1 = 0.0
    vx2 = 0.0
    vy2 = 0.3
    vz2 = 0.0
    '# initial masses For both stars
    m1 = 0.7
    m2 = 0.3
    rad1 = 0.1*m1
    rad2 = 0.1*m2
    '# arbitrary "Big G" gravitational constant
    G = 1.0
    '# calculate distance And r**3 denominator For universal
    '# gravitation
    r2 = (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2) + (z1-z2)*(z1-z2)
    r3 = r2*Sqr(r2)
    '# calculate acceleration components along x,y,z axes
    '# First For m1
    ax1 = -G*(x1-x2)*m2/r3
    ay1 = -G*(y1-y2)*m2/r3
    az1 = -G*(z1-z2)*m2/r3
    '# now For m2
    ax2 = -G*(x2-x1)*m1/r3
    ay2 = -G*(y2-y1)*m1/r3
    az2 = -G*(z2-z1)*m1/r3
    '# THIS Value keeps a smooth orbit On my workstation
    '# Smaller values slow down orbit, higher values speed up orbit
    dt = 0.04
    TBGL_BackColor(0,0,0)
    ' Resets status of all keys
    TBGL_ResetKeyState()
    End Sub

    Sub PlotFunc()
    ' -- Which window is calling?
    Local hWnd As DWord = TBGL_CallingWindow
    ' TBGL_Camera( x, y, z, x2, y2, z2 )
    ORBITS()
    TBGL_ClearFrame '(%TBGL_CLEAR_Color)

    TBGL_Camera(0.0, 0.0, 3.0, 0.0, 0.0, 0.0)


    TBGL_PushMatrix
    TBGL_Translate(x1,y1,z1)
    TBGL_Color(245, 230, 100)
    TBGL_Sphere(Rad1)
    TBGL_PopMatrix

    '# plot the second star (m2) position

    TBGL_PushMatrix
    TBGL_Translate(x2,y2,z2)
    TBGL_Color(245, 150, 100)
    TBGL_Sphere(Rad2)
    TBGL_PopMatrix

    TBGL_DrawFrame

    ' ESCAPE key to disable callback
    If TBGL_GetWindowKeyState(hWnd, %VK_ESCAPE) Then
    TBGL_UnBindPeriodicFunction( hWnd )
    Exit Sub
    End If

    End Sub

    Sub orbits()
    '# calculate front half of velocity vector components
    vx1 += 0.5*ax1*dt
    vy1 += 0.5*ay1*dt
    vz1 += 0.5*az1*dt
    vx2 += 0.5*ax2*dt
    vy2 += 0.5*ay2*dt
    vz2 += 0.5*az2*dt
    '# calculate x,y,z positions For both stars
    x1 += vx1*dt
    y1 += vy1*dt
    z1 += vz1*dt
    x2 += vx2*dt
    y2 += vy2*dt
    z2 += vz2*dt
    '# calculate the New r**3 denominator For each star position
    r2 = (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2) + (z1-z2)*(z1-z2)
    r3 = r2*Sqr(r2)
    '# calculate the New acceleration components
    ax1 = -G*(x1-x2)*m2/r3
    ay1 = -G*(y1-y2)*m2/r3
    az1 = -G*(z1-z2)*m2/r3
    ax2 = -G*(x2-x1)*m1/r3
    ay2 = -G*(y2-y1)*m1/r3
    az2 = -G*(z2-z1)*m1/r3
    '# calculate the back half velocity components
    vx1 += 0.5*ax1*dt
    vy1 += 0.5*ay1*dt
    vz1 += 0.5*az1*dt
    vx2 += 0.5*ax2*dt
    vy2 += 0.5*ay2*dt
    vz2 += 0.5*az2*dt
    '#Send calculated x,y,z star positions To the display
    'glutPostRedisplay()
    End Sub

    [/code]
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    Re: Example: Section 8.3 (page 265), A little MORE Gravity! 2 Bodies

    Again thanks Michael, fun to see these conversions and what is coming up in the book!!
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