Double Buffering in VB6

[CodeMonkey2000]

Is there any way of getting rid of the screen flicker? Also is there a way to take a screen shot of your VB form (similar to turing's pic.new)?

[CodeMonkey2000]

No suggestions?

[Nick]

no idea did u try using the search feature or looking at some tuturials?

[cpu_hacker4.0]

yeah ive always wondered about double buffering in vb

[CodeMonkey2000]

Apparently you can't, not in VB6 anyway.

[Euphoracle]

DoubleBuffering is just drawing to an offscreen image and then drawing that image to the screen at one time, so it's not drawing bit-by-bit, but instead as a whole. I KNOW this is possible because I friend made a "3D" 2D tunnel in VB6 and sent it to me. It's just not given to you like in .Net (You can set Control.DoubleBuffered, which just wraps an offscreen image and sends that to paint instead of the plain Graphics object).

Here, I did it in Java (because that's what I'm learning for school) to demonstrate how it can be done manually.

Java:

/*  * Drawable Base Frame :D  * */ // Imports import java.awt.*; // Application class DrawableFrame2D extends Frame {         // Buffers, fixes flickering     private Graphics gBuffer;     private Image iBuffer;         // Defaults     private final Point DEFAULT_POS = new Point( 200, 200 );     private final Point DEFAULT_SIZE = new Point( 640, 480 );     private final Color DEFAULT_BACK_COLOR = Color.WHITE;         public static void main( String[] arg )     {                 // DrawableFrame2D App = new DrawableFrame2D( "Drawable Base Test!", true );             }         public DrawableFrame2D( String title, boolean max )     {                 // Title bar         setUndecorated( true );                 // Perform the form init requirements         setTitle( title );         setVisible( true );                 // Size based on maximized         if ( max )         {                         // Get the current resolution             Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();             setBounds( 0, 0, screenSize.width, screenSize.height - 20 );                     }         else             setBounds( DEFAULT_POS.x, DEFAULT_POS.y, DEFAULT_SIZE.x, DEFAULT_SIZE.y );                 setBackground( DEFAULT_BACK_COLOR );                 // Stuff we don't mess with         setLocationRelativeTo( null );             }         // Fixes the flicker bug, I hope :)     public void update( Graphics g )     {                 // Recreate our buffers         if ( iBuffer == null )             iBuffer = createImage( getSize( ).width, getSize( ).height );                 gBuffer = iBuffer.getGraphics( );                 // Call paint with our buffer         paint( gBuffer );                 // Paint our buffer         g.drawImage( iBuffer, 0, 0, this );                 // Kill us, so we can be recreated later         gBuffer.dispose( );             }     }

As you can see, this is a very crude example that bases itself off a Panel. paint is an abstract method that is forced to be call. Essentially, all you'd have to do is make a class based on Form, override update to use your doublebuffer, call the base, just to make sure you didn't forget anything, and then draw your image, unless, of course, you can't do any of that in VB6 (the way I described it) in which case: ( X _ x )

Find your equivalent VB6 classes, and code away :V

[Brightguy]

Well how about that, I never knew "Double Buffering" had a name... but here's an example of how to do it in classic VB, just change the filename variable to point to a picture.

VisualBASIC:

Option Explicit Private Const filename = "C:\picture.jpg" Private backDC As Long, picDC As Long, picInfo As BITMAP Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal X As Long, ByVal Y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long Private Declare Function CreateCompatibleBitmap Lib "gdi32" (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight As Long) As Long Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long Private Declare Function GetDC Lib "user32" (ByVal hwnd As Long) As Long Private Declare Function GetObject Lib "gdi32.dll" Alias "GetObjectA" (ByVal hObject As Long, ByVal nCount As Long, ByRef lpObject As Any) As Long Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long Private Type BITMAP     bmType As Long     bmWidth As Long     bmHeight As Long     bmWidthBytes As Long     bmPlanes As Integer     bmBitsPixel As Integer     bmBits As Long End Type Private Sub Form_Load()     'Damn twips     Me.ScaleMode = vbPixels     'Load the picture into the device context and retrieve info     picDC = CreateCompatibleDC(GetDC(0))     SelectObject picDC, LoadPicture(filename)     GetObject LoadPicture(filename), Len(picInfo), picInfo         'Create device context for the background     backDC = CreateCompatibleDC(GetDC(0)) End Sub Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)     'Draw picture on background     BitBlt backDC, X - Int(picInfo.bmWidth / 2), Y - Int(picInfo.bmHeight / 2), picInfo.bmWidth, picInfo.bmHeight, picDC, 0, 0, vbSrcCopy     Form_Paint End Sub Private Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)     If Button > 0 Then         'Draw picture on background         BitBlt backDC, X - Int(picInfo.bmWidth / 2), Y - Int(picInfo.bmHeight / 2), picInfo.bmWidth, picInfo.bmHeight, picDC, 0, 0, vbSrcCopy         Form_Paint     End If End Sub Private Sub Form_Paint()     'Draw background on form     BitBlt Me.hdc, 0, 0, Me.ScaleWidth, Me.ScaleHeight, backDC, 0, 0, vbSrcCopy End Sub Private Sub Form_Resize()     'Create bitmap of proper size for the background     Dim backBitmap As Long     backBitmap = CreateCompatibleBitmap(GetDC(0), Me.ScaleWidth, Me.ScaleHeight)     SelectObject backDC, backBitmap     DeleteObject backBitmap         'Draw picture in the middle of background     BitBlt backDC, Int((Me.ScaleWidth - picInfo.bmWidth) / 2), Int((Me.ScaleHeight - picInfo.bmHeight) / 2), picInfo.bmWidth, picInfo.bmHeight, picDC, 0, 0, vbSrcCopy     Form_Paint End Sub Private Sub Form_Unload(Cancel As Integer)     'Cleanup memory     DeleteDC backDC     DeleteDC picDC End Sub

[CodeMonkey2000]

Wow thanks Brightguy. What's gdi32? Is that like SDL? Can I use SDL instead?

[rdrake]

CodeMonkey2000 @ Sat Oct 13, 2007 8:21 pm wrote:

Wow thanks Brightguy. What's gdi32? Is that like SDL? Can I use SDL instead?

Graphical Device Interface. It's used by Windows to draw graphics on the monitor and to output graphics to printers and such.

[CodeMonkey2000]

Why doesn't this work?

VisualBASIC:

Option Explicit Private Declare Function LineTo Lib "gdi32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long) As Long Private Declare Function MoveToEx Lib "gdi32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long, lpPoint As Any) As Long Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long Private Declare Function CreatePen Lib "gdi32" (ByVal nPenStyle As Long, ByVal nWidth As Long, ByVal crColor As Long) As Long Dim redPen As Long Dim mousePress As Boolean Private Sub Form_Load()    redPen = CreatePen(0, 15, vbRed)    DeleteObject SelectObject(hdc, redPen)    mousePress = False End Sub Private Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)    If Button > 1 And Not mousePress Then       MoveToEx hdc, X, Y, 0       LineTo hdc, X, Y    ElseIf Button > 1 And mousePress Then       LineTo hdc, X, Y    Else       mousePress = False    End If    Refresh End Sub

[Brightguy]

A few things:

-Make sure ScaleMode is in pixels
-Don't use Refresh unless AutoRedraw is true
-Button > 1 doesn't recognize left clicks
-mousePress will never be true

[CodeMonkey2000]

Thanks. For those interested, here is a decent reference for gdi32 commands.