i've been programming with Bitblt (VB6) for a while and i'm trying to learn DirectDraw7.

I'm trying to use BltFast to convert this background into a tiled map.

actually, i was sucessfull of making tiles, but when the sprites run over the background i get visual errors,

so it seems i'm having problems with refreshing the background.

here's the unedited code i started with.

my question is, what do i have to change to make this a tiled map in BltFast?

Option Explicit
Option Base 0

'Windows API functions and structures
Private Declare Function GetTickCount _
    Lib "kernel32" () As Long

'program constants
Const SCREENWIDTH As Long = 640
Const SCREENHEIGHT As Long = 480
Const MAXFRAMERATE As Long = 100
Const NUMSPRITES As Long = 30

'program controls
Dim WithEvents Picture1 As PictureBox

'DirectDraw variables
Dim objDX As DirectX7
Dim ddraw As DirectDraw7
Dim objDDClip As DirectDrawClipper
Private ddcKey As DDCOLORKEY

'primary display surface variables
Dim ddScreen As DirectDrawSurface7
Private ddsdScreen As DDSURFACEDESC2
Private rScreen As RECT

'double buffer variables
Dim ddBackBuffer As DirectDrawSurface7
Private ddsdBackBuffer As DDSURFACEDESC2
Dim rBackBuffer As RECT

'background image variables
Dim ddBackground As DirectDrawSurface7
Private ddsdBackground As DDSURFACEDESC2
Dim rBackground As RECT

'sprite variables
Dim ddSprites(NUMSPRITES) As DirectDrawSurface7
Dim SpriteX(NUMSPRITES) As Long
Dim SpriteY(NUMSPRITES) As Long
Dim SpeedX(NUMSPRITES) As Long
Dim SpeedY(NUMSPRITES) As Long
Private ddsdSprite As DDSURFACEDESC2
Dim rSprite As RECT

'program variables
Dim rTemp As RECT
Dim bRunning As Boolean
Dim n As Long

Private Sub Form_Load()
    Static lStartTime As Long
    Static lCounter As Long
    Static lNewTime As Long
   
    bRunning = True
    Randomize GetTickCount
   
    'set up the main form
    With Form1
        .Width = SCREENWIDTH * Screen.TwipsPerPixelX
        .Height = SCREENHEIGHT * Screen.TwipsPerPixelY
        .AutoRedraw = False
        .ClipControls = False
        .KeyPreview = True
        .ScaleMode = 3
        .BorderStyle = 1
        .Show
    End With

    'create the PictureBox control
    Set Picture1 = Controls.Add("VB.PictureBox", "Picture1")
    With Picture1
        .AutoRedraw = False
        .BorderStyle = 1
        .ClipControls = False
        .ScaleMode = 3
        .BackColor = RGB(0, 0, 0)
        .Left = 0
        .Top = 0
        .Width = Form1.ScaleWidth
        .Height = Form1.ScaleHeight
        .Visible = True
    End With

    'create the DirectX object
    Set objDX = New DirectX7
   
    'create the DirectDraw object
    Set ddraw = objDX.DirectDrawCreate("")

    'set up primary display surface
    ddraw.SetCooperativeLevel Picture1.hWnd, DDSCL_NORMAL
    ddsdScreen.lFlags = DDSD_CAPS
    ddsdScreen.ddsCaps.lCaps = DDSCAPS_PRIMARYSURFACE
    ddsdScreen.lWidth = SCREENWIDTH
    ddsdScreen.lHeight = SCREENHEIGHT
    Set ddScreen = ddraw.CreateSurface(ddsdScreen)
   
    'set surface rectangle
    rScreen.Bottom = ddsdScreen.lHeight
    rScreen.Right = ddsdScreen.lWidth
   
    'create the clipper object
    Set objDDClip = ddraw.CreateClipper(0)
    objDDClip.SetHWnd Picture1.hWnd
    ddScreen.SetClipper objDDClip
   
    'create the back buffer
    ddsdBackBuffer.lFlags = DDSD_CAPS Or DDSD_WIDTH Or DDSD_HEIGHT
    ddsdBackBuffer.ddsCaps.lCaps = DDSCAPS_OFFSCREENPLAIN
    ddsdBackBuffer.lWidth = SCREENWIDTH
    ddsdBackBuffer.lHeight = SCREENHEIGHT
    Set ddBackBuffer = ddraw.CreateSurface(ddsdBackBuffer)
    rBackBuffer.Bottom = ddsdBackBuffer.lHeight
    rBackBuffer.Right = ddsdBackBuffer.lWidth
   
    'load the background image
    ddsdBackground.lFlags = DDSD_CAPS Or DDSD_WIDTH Or DDSD_HEIGHT
    ddsdBackground.ddsCaps.lCaps = DDSCAPS_OFFSCREENPLAIN
    ddsdBackground.lWidth = SCREENWIDTH
    ddsdBackground.lHeight = SCREENHEIGHT
    Set ddBackground = ddraw.CreateSurfaceFromFile(App.Path & _
        "\blueyellow.bmp", ddsdBackground)
    rBackground.Bottom = ddsdBackground.lHeight
    rBackground.Right = ddsdBackground.lWidth
    ddBackBuffer.BltFast 0, 0, ddBackground, rBackground, _
        DDBLTFAST_WAIT
   
    'set up the sprite information
    ddsdSprite.lFlags = DDSD_CAPS Or DDSD_WIDTH Or DDSD_HEIGHT
    ddsdSprite.ddsCaps.lCaps = DDSCAPS_OFFSCREENPLAIN
    ddsdSprite.lWidth = 64
    ddsdSprite.lHeight = 64
    ddcKey.low = 0
    ddcKey.high = 0
   
    'load the sprites
    For n = 0 To NUMSPRITES
        Set ddSprites(n) = ddraw.CreateSurfaceFromFile(App.Path & _
            "\directx.bmp", ddsdSprite)
        rSprite.Bottom = ddsdSprite.lHeight
        rSprite.Right = ddsdSprite.lWidth
        SpriteX(n) = Random(SCREENWIDTH - ddsdSprite.lWidth)
        SpriteY(n) = Random(SCREENHEIGHT - ddsdSprite.lHeight)
        Do Until SpeedX(n) <> 0
            SpeedX(n) = Random(6) - 3
        Loop
        Do Until SpeedY(n) <> 0
            SpeedY(n) = Random(6) - 3
        Loop
        ddSprites(n).SetColorKey DDCKEY_SRCBLT, ddcKey
    Next n
   
    'main game loop
    Do While bRunning
        lCounter = GetTickCount - lStartTime
        If lCounter > lNewTime Then
            'update game display
            Game_Update lCounter
            'update frame count
            lNewTime = lCounter + 1000 / MAXFRAMERATE
        End If
        DoEvents
    Loop
   
End Sub

Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
    If KeyCode = 27 Then Shutdown
End Sub

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
    Shutdown
End Sub

Private Sub Form1_Click()
    Shutdown
End Sub

Private Sub Picture1_Click()
    Shutdown
End Sub

Private Sub Shutdown()
    bRunning = False
    Form1.Hide
    ddraw.RestoreDisplayMode
    ddraw.SetCooperativeLevel Picture1.hWnd, DDSCL_NORMAL
    Set ddraw = Nothing
    Set objDX = Nothing
    End
End Sub

Public Function Random(ByVal lNum As Long) As Long
    Random = CLng(lNum * Rnd)
End Function

Public Sub Game_Update(ByVal MS As Long)
    Static lTimer As Long
    Static lStart As Long
    Static lCounter As Long

    'start counting draw time
    lStart = GetTickCount

    'erase sprites
    For n = 0 To NUMSPRITES
        rTemp.Left = SpriteX(n)
        rTemp.Top = SpriteY(n)
        rTemp.Right = rTemp.Left + ddsdSprite.lWidth
        rTemp.Bottom = rTemp.Top + ddsdSprite.lHeight
        ddBackBuffer.BltFast SpriteX(n), SpriteY(n), ddBackground, _
            rTemp, DDBLTFAST_WAIT
    Next n
   
    'move and draw the sprites
    For n = 0 To NUMSPRITES
        'update X position
        SpriteX(n) = SpriteX(n) + SpeedX(n)
        If SpriteX(n) < 1 Then
            SpeedX(n) = -SpeedX(n)
            SpriteX(n) = 1
        ElseIf SpriteX(n) + ddsdSprite.lWidth > SCREENWIDTH Then
            SpeedX(n) = -SpeedX(n)
            SpriteX(n) = SCREENWIDTH - ddsdSprite.lWidth - 1
        End If

        'update Y position
        SpriteY(n) = SpriteY(n) + SpeedY(n)
        If SpriteY(n) < 1 Then
            SpeedY(n) = -SpeedY(n)
            SpriteY(n) = 1
        ElseIf SpriteY(n) + ddsdSprite.lHeight > SCREENHEIGHT Then
            SpeedY(n) = -SpeedY(n)
            SpriteY(n) = SCREENHEIGHT - ddsdSprite.lHeight - 1
        End If

        'draw the sprite
        rTemp.Left = SpriteX(n)
        rTemp.Top = SpriteY(n)
        rTemp.Right = SpriteX(n) + ddsdSprite.lWidth
        rTemp.Bottom = SpriteY(n) + ddsdSprite.lHeight
        ddBackBuffer.Blt rTemp, ddSprites(n), rSprite, _
            DDBLT_WAIT Or DDBLT_KEYSRC
    Next n
   
    'copy double buffer to the screen
    objDX.GetWindowRect Picture1.hWnd, rScreen
    ddScreen.Blt rScreen, ddBackBuffer, rBackBuffer, DDBLT_WAIT

    'count the frames per second
    If MS > lTimer + 1000 Then
        lStart = GetTickCount - lStart
        Form1.Caption = "FPS = " & lCounter & ", MS = " & lStart
        lTimer = MS
        lCounter = 0
    Else
        lCounter = lCounter + 1
    End If
End Sub