[RESOLVED] Math Issues With Boxes.....

I'm trying to implement Sweep AABB collisions for the first time based on this gamedev article:
http://www.gamedev.net/page/resource...response-r3084

And what this is used for is collisions for fast moving objects. If you were to use a simple bounding box check, itll never register a collision because the object goes through the object. Sweep AABB helps prevent that.

However I ran into a snag. His broadphase box is wrong. What a broadphase box is, is a box that is invisible but is used for collision by creating a box combining the old position and new position after moving which looks like this:

The broadphase box in the article on the otherhand is backwards:

Code:

Box GetSweptBroadphaseBox(Box b)

{

    Box broadphasebox;

    broadphasebox.x = b.vx > 0 ? b.x : b.x + b.vx;

    broadphasebox.y = b.vy > 0 ? b.y : b.y + b.vy;

    broadphasebox.w = b.vx > 0 ? b.vx + b.w : b.w - b.vx;

    broadphasebox.h = b.vy > 0 ? b.vy + b.h : b.h - b.vy;



    return broadphasebox;

}

Where x and y are positions, w and h are width and height, and vx and vy are velocities. What this does is that it puts the box in front of the box rather than trail behind. This means that a collision will occur before the object will actually collide into the object! I created the same code only a tad different:

vb Code:

Private Function GetSweptBroadphaseBox(B As Sprite_Type) As Sprite_Type
    Dim broadphasebox As Sprite_Type
    
    With broadphasebox
        If B.Velocity.X > 0 Then
            .Position.X = B.Position.X
            .Width = B.Velocity.X + B.Width
        ElseIf B.Velocity.X < 0 Then
            .Position.X = B.Position.X + B.Velocity.X
            .Width = B.Width - B.Velocity.X
        Else
            .Position.X = B.Position.X
            .Width = B.Width
        End If
        
        If B.Velocity.Y > 0 Then
            .Position.Y = B.Position.Y
            .Height = B.Velocity.Y + B.Height
        ElseIf B.Velocity.Y < 0 Then
            .Position.Y = B.Position.Y + B.Velocity.Y
            .Height = B.Height - B.Velocity.Y
        Else
            .Position.Y = B.Position.Y
            .Height = B.Height
        End If
    End With
    GetSweptBroadphaseBox = broadphasebox
End Function

Now its the same code but I want the box to trail behind and look like the picture I have above rather than have the broadphase box heading up front. I tried playing with it and adding different things but it ended up a complete mess. If anyone whos got bigger brains than I do, I could sure use some help. Thanks in advance :bigyello:

Also here is the code I currently have:

vb Code:

Option Explicit
 
Private Type Vector2D
    X As Single
    Y As Single
End Type
 
Private Type Sprite_Type
    Old_Position As Vector2D
    Position As Vector2D
    Width As Long
    Height As Long
    Velocity As Vector2D
    Speed As Long
    Normal As Vector2D
    Color As Long
End Type
 
Private Declare Function timeGetTime Lib "winmm.dll" () As Long
 
Private Player As Sprite_Type
Private Monster As Sprite_Type
 
Private Const BUTTON_UP As Long = vbKeyW
Private Const BUTTON_DOWN As Long = vbKeyS
Private Const BUTTON_LEFT As Long = vbKeyA
Private Const BUTTON_RIGHT As Long = vbKeyD
 
Private Const BUTTON_UP_FLAG As Long = 1
Private Const BUTTON_DOWN_FLAG As Long = 2
Private Const BUTTON_LEFT_FLAG As Long = 4
Private Const BUTTON_RIGHT_FLAG As Long = 8
 
Private INFINITY As Double
Private NEG_INFINITY As Double
 
Private Running As Boolean
Private Key_State As Long
 
Private Milliseconds As Long
Private Get_Frames_Per_Second As Long
Private Frame_Count As Long
 
Dim xInvEntry As Single, yInvEntry As Single
Dim xInvExit As Single, yInvExit As Single
Dim xEntry As Single, yEntry As Single
Dim xExit As Single, yExit As Single
Dim entryTime As Single
Dim exitTime As Single
 
Private Function Get_Elapsed_Time() As Single
    Dim Current_Time As Long
 
    Current_Time = timeGetTime
    Get_Elapsed_Time = CSng(Current_Time) / 1000
End Function
 
Private Sub Lock_Framerate(ByVal Target_FPS As Long)
    Static Last_Time As Long
    Dim Current_Time As Long
    Dim FPS As Single
 
    Do
        Current_Time = timeGetTime
        FPS = 1000 / CSng(Current_Time - Last_Time)
    Loop While (FPS > Target_FPS)
 
    Last_Time = timeGetTime
End Sub
 
Private Function Get_FPS() As String
    Frame_Count = Frame_Count + 1
 
    If Get_Elapsed_Time() - Milliseconds >= 1 Then
        Get_Frames_Per_Second = Frame_Count
        Frame_Count = 0
        Milliseconds = Convert.ToInt32(Get_Elapsed_Time)
    End If
 
    Get_FPS = "Frames Per Second: " & Csngg(Get_Frames_Per_Second)
End Function
 
Public Sub Setup_Infinity()
  On Error Resume Next
  INFINITY = 1 / 0
  On Error GoTo 0
  NEG_INFINITY = -INFINITY
End Sub
 
Private Function Max(A As Single, B As Single) As Single
    If A >= B Then Max = A Else Max = B
End Function
 
Private Function Min(A As Single, B As Single) As Single
    If A <= B Then Min = A Else Min = B
End Function
 
Private Sub Get_Velocity(Sprite As Sprite_Type)
    With Sprite
        .Velocity.X = .Position.X - .Old_Position.X
        .Velocity.Y = .Position.Y - .Old_Position.Y
    End With
End Sub
 
Private Function AABBCheck(B1 As Sprite_Type, B2 As Sprite_Type) As Boolean
    AABBCheck = Not (B1.Position.X + B1.Width < B2.Position.X Or _
                     B1.Position.X > B2.Position.X + B2.Width Or _
                     B1.Position.Y + B1.Height < B2.Position.Y Or _
                     B1.Position.Y > B2.Position.Y + B2.Height)
End Function
 
Private Function GetSweptBroadphaseBox(B As Sprite_Type) As Sprite_Type
    Dim broadphasebox As Sprite_Type
    
    With broadphasebox
        If B.Velocity.X > 0 Then
            .Position.X = B.Position.X
            .Width = B.Velocity.X + B.Width
        ElseIf B.Velocity.X < 0 Then
            .Position.X = B.Position.X + B.Velocity.X
            .Width = B.Width - B.Velocity.X
        Else
            .Position.X = B.Position.X
            .Width = B.Width
        End If
        
        If B.Velocity.Y > 0 Then
            .Position.Y = B.Position.Y
            .Height = B.Velocity.Y + B.Height
        ElseIf B.Velocity.Y < 0 Then
            .Position.Y = B.Position.Y + B.Velocity.Y
            .Height = B.Height - B.Velocity.Y
        Else
            .Position.Y = B.Position.Y
            .Height = B.Height
        End If
    End With
    GetSweptBroadphaseBox = broadphasebox
End Function
 
Private Function Sweep_Collision_Detection(B1 As Sprite_Type, B2 As Sprite_Type) As Single
 
    'find the distance between the objects on the near and far sides for both x and y
    If B1.Velocity.X > 0 Then
        xInvEntry = B2.Position.X - (B1.Position.X + B1.Width)
        xInvExit = (B2.Position.X + B2.Width) - B1.Position.X
    Else
        xInvEntry = (B2.Position.X + B2.Width) - B1.Position.X
        xInvExit = B2.Position.X - (B1.Position.X + B1.Width)
    End If
 
    If B1.Velocity.Y > 0 Then
        yInvEntry = B2.Position.Y - (B1.Position.Y + B1.Height)
        yInvExit = (B2.Position.Y + B2.Height) - B1.Position.Y
    Else
        yInvEntry = (B2.Position.Y + B2.Height) - B1.Position.Y
        yInvExit = B2.Position.Y - (B1.Position.Y + B1.Height)
    End If
    
    'find time of collision and time of leaving for each axis (if statement is to prevent divide by zero)
 
    If B1.Velocity.X = 0 Then
        xEntry = CSng(NEG_INFINITY)
        xExit = CSng(INFINITY)
    Else
        xEntry = xInvEntry / B1.Velocity.X
        xExit = xInvExit / B1.Velocity.X
    End If
 
    If B1.Velocity.Y = 0 Then
        yEntry = CSng(NEG_INFINITY)
        yExit = CSng(INFINITY)
    Else
        yEntry = yInvEntry / B1.Velocity.Y
        yExit = yInvExit / B1.Velocity.Y
    End If
    
    entryTime = Max(xEntry, yEntry)
    exitTime = Min(xExit, yExit)
    
    If entryTime > exitTime Then
        Sweep_Collision_Detection = 1
        Exit Function
    End If
    
    If (xEntry < 0 And yEntry < 0) Then
        Sweep_Collision_Detection = 1
        Exit Function
    End If
    
    If xEntry < 0 Then
        If (B1.Position.X + B1.Width) < B2.Position.X Or B1.Position.X > (B2.Position.X + B2.Width) Then
            Sweep_Collision_Detection = 1
            Exit Function
        End If
    End If
    
    'if there was a collision
    'calculate normal of collided surface
    If xEntry > yEntry Then
        If xInvEntry < 0 Then
            B1.Normal.X = 1
            B1.Normal.Y = 0
        Else
            B1.Normal.X = -1
            B1.Normal.Y = 0
        End If
    Else
        If yInvEntry < 0 Then
            B1.Normal.X = 0
            B1.Normal.Y = 1
        Else
            B1.Normal.X = 0
            B1.Normal.Y = -1
        End If
    End If
    
    'return the time of collision
    Sweep_Collision_Detection = entryTime
 
End Function
 
Private Function Check_Key(Key_Flag As Long) As Long
    Check_Key = Key_State And Key_Flag
End Function
 
Private Sub Keyboard_Controls()
    
    With Player
        If Check_Key(BUTTON_UP_FLAG) Then
            .Position.Y = .Position.Y - .Speed
        End If
                
        If Check_Key(BUTTON_DOWN_FLAG) Then
            .Position.Y = .Position.Y + .Speed
        End If
                
        If Check_Key(BUTTON_LEFT_FLAG) Then
            .Position.X = .Position.X - .Speed
        End If
                
        If Check_Key(BUTTON_RIGHT_FLAG) Then
            .Position.X = .Position.X + .Speed
        End If
    End With
End Sub
 
Private Sub Draw_Rectangle(ByVal X As Long, ByVal Y As Long, ByVal Width As Long, ByVal Height As Long, ByVal Color As Long)
    frmMain.Line (X, Y)-(X + Width, Y + Height), Color, B
End Sub
 
Private Sub Draw_Filled_Rectangle(ByVal X As Long, ByVal Y As Long, ByVal Width As Long, ByVal Height As Long, ByVal Color As Long)
    frmMain.Line (X, Y)-(X + Width, Y + Height), Color, BF
End Sub
 
Private Sub Main()
    With frmMain
        .Show
        .BackColor = RGB(0, 0, 0)
        .ForeColor = RGB(0, 255, 0)
        .ScaleMode = vbPixels
        .AutoRedraw = True
    End With
    
    With Player
        .Width = 30
        .Height = 30
        .Position.X = (frmMain.ScaleWidth / 2) - (.Width / 2)
        .Position.Y = (frmMain.ScaleHeight / 2) - (.Height / 2)
        .Color = RGB(0, 55, 0)
        .Speed = 10
    End With
    
    With Monster
        .Width = 30
        .Height = 30
        .Position.X = (frmMain.ScaleWidth / 2) - (.Width / 2) + 50
        .Position.Y = (frmMain.ScaleHeight / 2) - (.Height / 2)
        .Color = RGB(255, 0, 0)
        .Speed = 1
    End With
    
    Setup_Infinity
    Milliseconds = Get_Elapsed_Time
    Running = True
    
    Do While Running = True
        frmMain.Cls
        Player.Old_Position = Player.Position
        Keyboard_Controls
        Get_Velocity Player
        Dim broadphasebox As Sprite_Type
        broadphasebox = GetSweptBroadphaseBox(Player)
        If AABBCheck(broadphasebox, Monster) Then frmMain.Caption = "hit" Else frmMain.Caption = "Form1" 'Sweep_Collision_Detection Player, Monster
        'frmMain.Caption = Sweep_Collision_Detection(Player, Monster)
        'frmMain.Print entryTime, exitTime
        'frmMain.Print xEntry, xExit
        'frmMain.Print xExit, yExit
        'frmMain.Print Player.Velocity.X, Player.Velocity.Y
        Draw_Filled_Rectangle Monster.Position.X, Monster.Position.Y, Monster.Width, Monster.Height, Monster.Color
        Draw_Filled_Rectangle Player.Position.X, Player.Position.Y, Player.Width, Player.Height, Player.Color
        Draw_Rectangle broadphasebox.Position.X, broadphasebox.Position.Y, broadphasebox.Width, broadphasebox.Height, RGB(255, 255, 255)
        Lock_Framerate 60
        DoEvents
    Loop
End Sub
 
Private Sub Shutdown()
    Running = False
    Unload Me
End Sub
 
Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
    Select Case KeyCode
        Case BUTTON_UP
            Key_State = Key_State Or BUTTON_UP_FLAG
        Case BUTTON_DOWN
            Key_State = Key_State Or BUTTON_DOWN_FLAG
        Case BUTTON_LEFT
            Key_State = Key_State Or BUTTON_LEFT_FLAG
        Case BUTTON_RIGHT
            Key_State = Key_State Or BUTTON_RIGHT_FLAG
        Case vbKeyEscape
            Shutdown
    End Select
End Sub
 
Private Sub Form_KeyUp(KeyCode As Integer, Shift As Integer)
    Select Case KeyCode
        Case BUTTON_UP
            Key_State = Key_State And (Not BUTTON_UP_FLAG)
        Case BUTTON_DOWN
            Key_State = Key_State And (Not BUTTON_DOWN_FLAG)
        Case BUTTON_LEFT
            Key_State = Key_State And (Not BUTTON_LEFT_FLAG)
        Case BUTTON_RIGHT
            Key_State = Key_State And (Not BUTTON_RIGHT_FLAG)
    End Select
End Sub
 
Private Sub Form_Load()
    Main
End Sub
 
Private Sub Form_Unload(Cancel As Integer)
    Shutdown
End Sub

[RESOLVED] Math Issues With Boxes.....

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