2D Physics Engine

[TerryRitchie]

I made some modifications to the scene to play around with the physics.

I'm wondering about something curious that happens, I'll call it the "popcorn effect". If you start filing the room I created with objects at some point the objects seem to get extra impulse from somewhere. It looks like popcorn and doesn't stop until the end of object lifetimes starts removing them, allowing the scene to settle down.

Any idea why this happens? Are there settings to control this kind of chaos from happening?

Code: (Select All)

'**********************************************************************************************
'   fzxBareBones
'**********************************************************************************************

'$DYNAMIC
OPTION _EXPLICIT
_TITLE "fzxNGN Bare Bones"

' Initialize FZXNGN types, globals and constants
'$include:'..\fzxNGN_BASE_v2\fzxNGN_ini.bas'

SCREEN _NEWIMAGE(1024, 768, 32)

DIM AS LONG iterations: iterations = 2
DIM SHARED AS DOUBLE dt: dt = 1 / 60

'**********************************************************************************************
' Build the playfield
'**********************************************************************************************

buildScene

'**********************************************************************************************
' This is the main loop
'**********************************************************************************************

DO
    CLS
    fzxHandleInputDevice
    animatescene
    fzxImpulseStep dt, iterations
    renderBodies
    _DISPLAY
LOOP UNTIL INKEY$ = CHR$(27)

SYSTEM

' This provides access to all of the fzxNGN functionality
'$include:'..\fzxNGN_BASE_v2\fzxNGN_BASE.bas'

'**********************************************************************************************
'    This is where you interact with the world.
'**********************************************************************************************

SUB animatescene
    DIM AS LONG temp

    ' Create a object on mouse click
    IF __fzxInputDevice.mouse.b1.NegEdge THEN
        ' Drop a ball or a box, flip a coin
        IF RND > .5 THEN
            temp = fzxCreateCircleBodyEx("b" + _TRIM$(STR$(RND * 1000000000)), 20)
        ELSE
            temp = fzxCreateBoxBodyEx("b" + _TRIM$(STR$(RND * 1000000000)), 20, 20)
        END IF
        ' Set the bodies parameters
        ' Put the body where the mouse is on the screen
        fzxSetBody cFZX_PARAMETER_POSITION, temp, __fzxInputDevice.mouse.worldPosition.x, __fzxInputDevice.mouse.worldPosition.y
        ' Give it the mouse's velocity, so you can throw it
        fzxSetBody cFZX_PARAMETER_VELOCITY, temp, __fzxInputDevice.mouse.velocity.x, __fzxInputDevice.mouse.velocity.y
        ' Change its orientation or angle
        fzxSetBody cFZX_PARAMETER_ORIENT, temp, _D2R(RND * 360), 0
        ' Set the bouncyness
        fzxSetBody cFZX_PARAMETER_RESTITUTION, temp, .95, 0 ' Bounce
        ' Set the friction values of the body
        fzxSetBody cFZX_PARAMETER_STATICFRICTION, temp, .1, 0
        fzxSetBody cFZX_PARAMETER_DYNAMICFRICTION, temp, .85, 0
        ' Bodies wont live forever
        fzxSetBody cFZX_PARAMETER_LIFETIME, temp, RND * 20 + 10, 0
    END IF

END SUB

'********************************************************
'   Build you world here
'********************************************************

SUB buildScene
    DIM AS LONG temp

    'Initialize camera
    __fzxCamera.zoom = .5
    fzxCalculateFOV
    ' Set camera position
    fzxVector2DSet __fzxCamera.position, __fzxWorld.spawn.x, __fzxWorld.spawn.y - 300

    '********************************************************
    '   Setup World
    '********************************************************

    fzxVector2DSet __fzxWorld.minusLimit, -200000, -200000
    fzxVector2DSet __fzxWorld.plusLimit, 200000, 200000
    fzxVector2DSet __fzxWorld.spawn, 0, 0
    fzxVector2DSet __fzxWorld.gravity, 0.0, 10.0

    ' Some math used on the impulse side
    ' Todo: move this elsewhere
    DIM o AS tFZX_VECTOR2d
    fzxVector2DMultiplyScalarND o, __fzxWorld.gravity, dt
    __fzxWorld.resting = fzxVector2DLengthSq(o) + cFZX_EPSILON

    '********************************************************
    '   Build Level
    '********************************************************

    temp = fzxCreateBoxBodyEx("floor", 800, 10)
    fzxSetBody cFZX_PARAMETER_POSITION, temp, __fzxWorld.spawn.x, __fzxWorld.spawn.y
    fzxSetBody cFZX_PARAMETER_STATIC, temp, 0, 0


    temp = fzxCreateBoxBodyEx("Wall1", 10, 400)
    fzxSetBody cFZX_PARAMETER_POSITION, temp, __fzxWorld.spawn.x - 810, __fzxWorld.spawn.y - 390
    fzxSetBody cFZX_PARAMETER_STATIC, temp, 0, 0

    temp = fzxCreateBoxBodyEx("Wall2", 10, 400)
    fzxSetBody cFZX_PARAMETER_POSITION, temp, __fzxWorld.spawn.x + 810, __fzxWorld.spawn.y - 390
    fzxSetBody cFZX_PARAMETER_STATIC, temp, 0, 0

    temp = fzxCreateBoxBodyEx("Ceiling", 800, 10)
    fzxSetBody cFZX_PARAMETER_POSITION, temp, __fzxWorld.spawn.x, __fzxWorld.spawn.y - 780
    fzxSetBody cFZX_PARAMETER_STATIC, temp, 0, 0




END SUB

SUB renderBodies STATIC
    DIM i AS LONG
    DIM AS tFZX_VECTOR2d scSize, scMid, scUpperLeft, camUpperLeft, aabbUpperLeft, aabbSize, aabbHalfSize
    DIM AS LONG ub: ub = UBOUND(__fzxBody)

    ' Todo : move this to camera functions
    fzxVector2DSet aabbSize, 40000, 40000
    fzxVector2DSet aabbHalfSize, aabbSize.x / 2, aabbSize.y / 2

    fzxVector2DSet scUpperLeft, 0, 0
    fzxVector2DSet scSize, _WIDTH, _HEIGHT

    fzxVector2DDivideScalarND scMid, scSize, 2
    fzxVector2DSubVectorND camUpperLeft, __fzxCamera.position, scMid

    'Draw all of the bodies that are visible
    i = 0: DO WHILE i < ub
        IF __fzxBody(i).enable THEN
            'fzxAABB to cut down on rendering objects out of camera view
            fzxVector2DSubVectorND aabbUpperLeft, __fzxBody(i).fzx.position, aabbHalfSize
            IF fzxAABBOverlap(camUpperLeft.x, camUpperLeft.y, scSize.x, scSize.y, aabbUpperLeft.x, aabbUpperLeft.y, aabbSize.x, aabbSize.y) THEN
                IF __fzxBody(i).shape.ty = cFZX_SHAPE_CIRCLE THEN
                    renderWireFrameCircle i, _RGB32(0, 255, 0)
                ELSE IF __fzxBody(i).shape.ty = cFZX_SHAPE_POLYGON THEN
                        renderWireFramePoly i
                    END IF
                END IF
            END IF
        END IF
        i = i + 1
    LOOP

END SUB

SUB renderWireFrameCircle (index AS LONG, c AS LONG)
    DIM AS tFZX_VECTOR2d o1, o2
    fzxWorldToCameraEx __fzxBody(index).fzx.position, o1
    CIRCLE (o1.x, o1.y), __fzxBody(index).shape.radius * __fzxCamera.zoom, c
    o2.x = o1.x + (__fzxBody(index).shape.radius * __fzxCamera.zoom) * COS(__fzxBody(index).fzx.orient)
    o2.y = o1.y + (__fzxBody(index).shape.radius * __fzxCamera.zoom) * SIN(__fzxBody(index).fzx.orient)
    LINE (o1.x, o1.y)-(o2.x, o2.y), c
END SUB

SUB renderWireFramePoly (index AS LONG)
    DIM vert(3) AS tFZX_VECTOR2d

    fzxGetBodyVert index, 0, vert(0)
    fzxWorldToCamera index, vert(0)

    fzxGetBodyVert index, 1, vert(1)
    fzxWorldToCamera index, vert(1)

    fzxGetBodyVert index, 2, vert(2)
    fzxWorldToCamera index, vert(2)

    fzxGetBodyVert index, 3, vert(3)
    fzxWorldToCamera index, vert(3)

    LINE (vert(0).x, vert(0).y)-(vert(1).x, vert(1).y), _RGB(0, 255, 0)
    LINE (vert(1).x, vert(1).y)-(vert(2).x, vert(2).y), _RGB(0, 255, 0)
    LINE (vert(2).x, vert(2).y)-(vert(3).x, vert(3).y), _RGB(0, 255, 0)
    LINE (vert(3).x, vert(3).y)-(vert(0).x, vert(0).y), _RGB(0, 255, 0)
END SUB