How To Create Your Own Bitmap Object Class (187568)

MORE INFORMATION

This example shows how to build a simple Bitmap Object class, which allows you to load an image into the object, and use that image with the Bitblt API or any other drawing API which requires a Device Context. These objects are low in resource use and very fast. This example also shows how to create a Mask bitmap of an image (a Mask image can be used to perform transparency effects with bitmaps). Using an image Mask, you can easily perform fast transparent blitting.

The bitmap class has five properties and one function as listed below:

   Property GetImageDC    - Returns a DC to the actual image
   Property GetInvertedDC - Returns a DC to an inverted copy of the image
   Property GetMaskDC     - Returns a DC to a masked copy of the image
   Property Width         - Returns width (in pixels) of image
   Property Height        - Returns height (in pixels) of image
   Function SetBitmap     - Loads image, return TRUE if successful
				

Step-by-Step Example

1. Start a new Standard EXE project in Visual Basic 5.0. Form1 is created by default.
2. Add a module (Module1) and a class (Class1) to the project.
3. Add the following controls to Form1:

      1 Picturebox (make this control pretty large)
      1 Textbox
      4 CommandButtons
   
   					

4. Copy and paste the following code into the Module code window:

       Option Explicit
   
       ' constants used in this example are declared here
       Public Const SRCAND = &H8800C6 ' used to determine how a blit will
                                      ' turn out
       Public Const SRCCOPY = &HCC0020  ' used to determine how a blit
                                        ' will turn out
       Public Const SRCERASE = &H440328 ' used to determine how a blit
                                        ' will turn out
       Public Const SRCINVERT = &H660046  ' used to determine how a blit
                                          ' will turn out
       Public Const SRCPAINT = &HEE0086   ' used to determine how a blit
                                          ' will turn out
       Public Const IMAGE_BITMAP = &O0    ' used with LoadImage to load a
                                          ' bitmap
       Public Const LR_LOADFROMFILE = 16  ' used with LoadImage
   
       ' structures used in this example
       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
   
       ' API's used in this example
       Declare Function GetObject Lib "gdi32" Alias "GetObjectA" _
          (ByVal hObject As Long, ByVal nCount As Long, lpObject As Any) _
          As Long
       Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) _
          As Long
       Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) _
          As Long
       Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long
       Declare Function SelectObject Lib "gdi32" _
          (ByVal hdc As Long, ByVal hObject As Long) As Long
       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
       Declare Function SetBkColor Lib "gdi32" _
          (ByVal hdc As Long, ByVal crColor As Long) As Long
       Declare Function SetTextColor Lib "gdi32" _
          (ByVal hdc As Long, ByVal crColor As Long) As Long
       Declare Function LoadImage Lib "user32" Alias "LoadImageA" _
          (ByVal hInst As Long, ByVal lpsz As String, ByVal un1 As Long, _
          ByVal n1 As Long, ByVal n2 As Long, ByVal un2 As Long) As Long
       Declare Function CreateCompatibleBitmap Lib "gdi32" _
          (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight As Long) _
          As Long
   
   					

5. Rename Class1 to "clsBitmap", then copy and paste the following code in clsBitmap's code window:

   Option Explicit
   
   
          Private Const CLR_INVALID = &HFFFF ' used to test results of color
                                             ' API calls
   
          Private iImageDC As Long        ' DC to the Image bitmap
          Private iInvertImageDC As Long  ' DC to the Inverted Image bitmap
          Private iMaskDC As Long         ' DC to the Mask bitmap
          
          Private hbmImageOld As Long       'used to remove bitmaps
          Private hbmInvertImageOld As Long 'used to remove bitmaps
          Private hbmMaskOld As Long        'used to remove bitmaps
          
          Private iWidth As Long          ' Size of Bitmap - X
          Private iHeight As Long         ' Size of Bitmap - Y
          Private iInvertImage As Long    ' temp bitmap used in creating the
                                          ' invert image
          Private iMask As Long           ' temp bitmap used in creating mask
       
          ' For this object class, 5 properties are exposed (read only) and one
          ' function
   
          ' Get ImageDC           - returns a DC that contains the original
          '                         image
          ' Get InvertImageDC     - returns a DC that contains an invert of the
          '                         image's background
          ' Get MaskDC            - returns a DC that contains an invert of the
          '                         original image
          ' Fnc SetBitmap         - returns TRUE/FALSE when attempting to load
          '                         image into bitmap object
   
          Property Get ImageDC() As Long
             ImageDC = iImageDC              ' return the DC that contains the
                                             ' regular image
          End Property
   
          Property Get InvertImageDC() As Long
             InvertImageDC = iInvertImageDC  ' return the DC that contains the
                                             ' inverted image
          End Property
   
          Property Get MaskDC() As Long
             MaskDC = iMaskDC                ' return the DC that contains the
                                             ' mask image
          End Property
   
          Property Get Width() As Long
             Width = iWidth                  ' return the width of the bitmap
          End Property
   
          Property Get Height() As Long
             Height = iHeight                ' return the height of the bitmap
          End Property
   
          Public Function SetBitmap(NewBitmap As Long) As Boolean
   
          ' The NewBitmap argument is a handle to a bitmap. This is used to
          ' grab the bitmap info, place the data into a bitmap structure, and
          ' use the structure to build a bitmap/mask grab the bitmap
          ' information.
   
             Dim lresult As Long         ' lResults of our API calls
             Dim BitmapData As BITMAP    ' data on the incoming bitmap
             
             SetBitmap = True
             
             lresult = GetObject(NewBitmap, Len(BitmapData), BitmapData)
   
            ' Verify the bitmap data
               If (lresult = 0) Then
                  SetBitmap = False
               End If
   
             ' Persist the height/width of the bitmap image
   
             iWidth = BitmapData.bmWidth     ' Determine the bitmaps width
             iHeight = BitmapData.bmHeight    ' Determine the bitmaps height
   
          ' Three Device Contexts (DC) are created. One is temporary (for
          ' the incoming bitmap that will be copied. The second is for the
          ' bitmap image that will be contained with this bitmap object class,
          ' and the third is for the image mask that will also be contained
          ' within this bitmap object class.
   
          iImageDC = CreateCompatibleDC(0)
          iInvertImageDC = CreateCompatibleDC(0)
          iMaskDC = CreateCompatibleDC(0)
   
             ' Ensure that there are three new DCs to use in this bitmap object.
             If (iImageDC = 0) Or (iInvertImageDC = 0) Or (iMaskDC = 0) Then
                SetBitmap = False
             End If
   
          ' Save the actual bitmap within this bitmap object.
          hbmImageOld = SelectObject(iImageDC, NewBitmap)
   
          ' Make sure that the object is selected.
             If (lresult = 0) Then
                SetBitmap = False
             End If
   
          ' Create the bitmap to hold the inverted image, and connect it to a DC.
          iInvertImage = CreateCompatibleBitmap(iImageDC, iWidth, iHeight)
   
          ' Make sure that a bitmap can be created.
             If (iMask = 0) Then
                SetBitmap = False
             End If
   
          ' Copy the image into the bitmap that was just created.
             hbmInvertImageOld = SelectObject(iInvertImageDC, iInvertImage)
   
          ' Make sure that the object is selected.
             If (lresult = 0) Then
                SetBitmap = False
             End If
   
          ' Create the bitmap to hold the mask, and connect it to a DC.
             iMask = CreateCompatibleBitmap(iMaskDC, iWidth, iHeight)
   
          ' Make sure that a bitmap can be created.
             If (iMask = 0) Then
                SetBitmap = False
             End If
   
             ' The bitmap is now in memory. Attach it to the DC created for the Mask.
                hbmMaskOld = SelectObject(iMaskDC, iMask)
   
             ' Make sure that the object is selected.
                If (lresult = 0) Then
                   SetBitmap = False
                End If
   
             ' Blit the incoming image into the ImageDC created. Now there is a
             ' permanent copy of the original image.
             lresult = BitBlt(iInvertImageDC, 0, 0, iWidth, iHeight, iImageDC, _
                            0, 0, SRCCOPY)
   
             ' If the first blit fails, SetBitmap = False.
                If (lresult = 0) Then
                   SetBitmap = False
                End If
   
             ' Create the Mask image first.
               lresult = BitBlt(iMaskDC, 0, 0, iWidth, iHeight, iImageDC, 0, 0, _
                     SRCCOPY)
   
             ' If the first blit fails, SetBitmap = False.
                If (lresult = 0) Then
                   SetBitmap = False
                End If
   
             ' Next, change the background of the real bitmap. This is done to
             ' create the Mask image.
                lresult = SetBkColor(iInvertImageDC, vbBlack)
   
             ' Make sure that the background color is set successfully.
                If (lresult = CLR_INVALID) Then
                   SetBitmap = False
                End If
   
             ' Change the textcolor of the real bitmap. This is done to create
             ' the mask image.
             lresult = SetTextColor(iInvertImageDC, vbWhite)
   
             ' Make sure that the text color is set successfully.
                If (lresult = CLR_INVALID) Then
                   SetBitmap = False
                End If
   
             ' Invert the white background to black on the real bitmap by
             ' blitting the Mask that is created over the slightly modified 
             ' original bitmap. The background color becomes black -
             ' perfect for transparent blitting.
             lresult = BitBlt(iInvertImageDC, 0, 0, iWidth, iHeight, iMaskDC, _
                        0, 0, SRCAND)
   
             ' Make sure that the blit succeeded.
                If (lresult = 0) Then
                   SetBitmap = False
                End If
   
   
               lresult = DeleteObject(NewBitmap)
               
               ' Make sure that the temporary bitmap is deleted.
               If (lresult = 0) Then
                   SetBitmap = False
               End If
               
             ' The bitmap image has been loaded into the bitmap object,
             ' return a successful attempt.
   
          End Function
   
          Private Sub Class_Terminate()
           Dim lresult As Long
           
           lresult = DeleteObject(SelectObject(iImageDC, hbmImageOld))
           lresult = DeleteObject(SelectObject(iInvertImageDC, hbmInvertImageOld))
           lresult = DeleteObject(SelectObject(iMaskDC, hbmMaskOld))
           
           ' When this object is destroyed, destroy the Device Contexts that
           ' are being used.
           
           Call DeleteDC(iImageDC)         ' delete the image DC
           Call DeleteDC(iInvertImageDC)   ' delete the inverted image DC
           Call DeleteDC(iMaskDC)          ' delete the mask DC
   
          End Sub
   					

6. Copy and paste the following code into the Form1 code window:

       Option Explicit
   
       Private oTestBitmap As clsBitmap    ' sample bitmap object
   
       Private Sub Command1_Click()
          Dim hBitmap As Long     ' handle to bitmap being loaded
          Dim sFileName As String ' path + name of bitmap file to be loaded
          Dim bResult As Boolean  ' result of loading bitmap into bitmap
                                  ' object
       ' use the LoadImage API to load in a bitmap image. The name of the
       ' image file will be retrieved from the textbox control sited on the
       ' form.
   
       sFileName = Text1.Text
   
       ' call the LoadImage API to attempt to load in the test bitmap.
       hBitmap = LoadImage(0, sFileName, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE)
   
       ' if LoadImage fails, the return result is a zero, test for this
       ' before attempting to create our bitmap object.
   
         If (hBitmap = 0) Then
           MsgBox "Error : Unable To Load Bitmap Image : " & sFileName, _
               vbOKOnly, "Bitmap Load Error"
            Exit Sub
         End If
   
       ' create a new bitmap object for testing purposes
       Set oTestBitmap = New clsBitmap
   
       ' attempt to load the bitmap into to into the bitmap object using its
       ' handle
   
       bResult = oTestBitmap.SetBitmap(hBitmap)
   
       ' verify the image was successfully loaded into the bitmap object.
       ' SetBitmap returns true if successful.
   
          If (bResult = False) Then
            MsgBox "Error : Unable To Load Image Into Bitmap Object", _
                vbOKOnly, "Bitmap Object Error"
             Set oTestBitmap = Nothing
             Exit Sub
          End If
   
        ' test the bitmap object with the loaded image
        Command2.Enabled = True
        Command3.Enabled = True
        Command4.Enabled = True
   
       End Sub
   
       Private Sub Command2_Click()
   
          ' blit the bitmap object's image onto the picturebox
          Call BitBlt(Picture1.hdc, 10, 10, oTestBitmap.Width, _
          oTestBitmap.Height, oTestBitmap.ImageDC, 0, 0, SRCCOPY)
   
          ' refresh the picturebox to show the blit
          Picture1.Refresh
   
       End Sub
   
       Private Sub Command3_Click()
   
       ' blit the bitmap object's mask onto the picturebox
          Call BitBlt(Picture1.hdc, 10, 10, oTestBitmap.Width, _
          oTestBitmap.Height, oTestBitmap.MaskDC, 0, 0, SRCCOPY)
   
       ' refresh the picturebox to show the blit
          Picture1.Refresh
   
       End Sub
   
       Private Sub Command4_Click()
   
          ' demonstrate the transparency capabilities of the Bitmap Object
          ' class
   
          ' first, blit the mask to the Picture Box Control
            Call BitBlt(Picture1.hdc, 50, 10, oTestBitmap.Width, _
               oTestBitmap.Height, oTestBitmap.MaskDC, 0, 0, SRCAND)
   
          ' next blit the actual bitmap, which will fill in the black hole
          ' that the Mask image created in the Picturebox.
            Call BitBlt(Picture1.hdc, 50, 10, oTestBitmap.Width, _
               oTestBitmap.Height, oTestBitmap.InvertImageDC, 0, 0, SRCPAINT)
   
          ' refresh the Picturebox Control to show the effects
          Picture1.Refresh
   
       End Sub
   
       Private Sub Form_Load()
   
          ' disable the test buttons
          Command2.Enabled = False
          Command3.Enabled = False
          Command4.Enabled = False
   
          ' get the path of the test bitmap
          Text1.Text = App.Path & "\test.bmp"
   
          ' set the picturebox to autoredraw so the blits will show up
          Picture1.AutoRedraw = True
   
       End Sub
   
   					

7. Save and compile the project.

Creating a Test Bitmap

Use Microsoft Paint (MSPAINT.EXE) to create a bitmap with white (default) background and save it in the project's directory as TEST.BMP. Under Image menu, select Attributes to size the bitmap.

Running The Example

1. Press the F5 key while in the Visual Basic 5.0 to run the project.
2. Click "Command1" to load the bitmap.
3. Click "Command2" to blit the bitmap image to the picturebox.
4. Click "Command3" to blit the mask image to the picturebox.
5. Click "Command4" to show the transparent effect using both the mask image and the inverted image.

NOTE: The test bitmap must have all the "Transparent" pixels set to white. These white pixels will become the transparent part of the mask, and all the other pixels will be black when the mask is blitted.