How To Rotate a Bitmap Image in 90-Degree Increments (186260)


The information in this article applies to:

  • Microsoft Visual Basic Learning Edition for Windows 5.0
  • Microsoft Visual Basic Learning Edition for Windows 6.0
  • Microsoft Visual Basic Professional Edition for Windows 5.0
  • Microsoft Visual Basic Professional Edition for Windows 6.0
  • Microsoft Visual Basic Enterprise Edition for Windows 5.0
  • Microsoft Visual Basic Enterprise Edition for Windows 6.0
This article was previously published under Q186260

SUMMARY

Bitmap rotation is a graphic effect that Visual Basic does not natively offer. This article shows how to rotate a given image in 90-degree increments. It allows you to rotate any image 0, 90, 180 or 270 degrees. With a little work, the code can be modified to rotate to any angle, but that is beyond the scope of this article.

MORE INFORMATION

The following sample uses a function called RotateBitmap. Here is some information about this function: 
   RotateBitmap(hBitmapDC As Long, _
      lWidth As Long, _
      lHeight As Long, _
      lRadians As Long)
hBitmapDC: Handle to a device context of the image to be rotated. Upon return, this variable will contain the device context of the rotated image.

lWidth: Width of the incoming image. Upon return contains the width of the rotated image.

lHeight: Height of the incoming image. Upon return, contains the height of the rotated image.

lRadians: Angle to rotate the image (in Radians). The sample shows how to convert degrees into radians on the fly.

Step-by-Step Example

  1. Create a new Standard EXE project in Visual Basic. Form1 is created by default.
  2. Add a Standard Module (Module1) to the project.
  3. Add the following controls to Form1:

    • Two PictureBox controls
    • One Timer control
  4. For the two PictureBox controls, set their AutoRedraw properties to True.
  5. Copy and paste the following code in the Form's code Window: 
          Option Explicit

      Dim sFileName As String     ' filename of the image being used
      Dim hBitmap As Long         ' handle to the loaded bitmap
      Dim lBMDC As Long           ' device context of the bitmap
      Dim sBitmapInfo As BITMAP   ' information on the loaded image
      Dim Degrees As Long         ' current rotation degree

      Private Sub Form_Load()

         ' set staring degrees
         Degrees = 0

         ' set the bitmap that will be used in the sample
         sFileName = "filename.bmp"  ' where filename.bmp is the bitmap
                                     ' being used

         ' load the bitmap into memory
         hBitmap = LoadImage(0, sFileName, IMAGE_BITMAP, 0, 0, _
                     LR_LOADFROMFILE Or LR_CREATEDIBSECTION)

         ' make sure the call succeeded
         If (hBitmap = 0) Then
            MsgBox "Error, Unable To Load Bitmap", vbOKOnly, _
                   "Bitmap Load Error"
            End
         End If

         ' create a device context to use when blitting the loaded bitmap
         lBMDC = CreateCompatibleDC(0)

         ' make sure our call succeeded
         If (lBMDC = 0) Then
            MsgBox "Error, Unable To Create Device Context", _
                   vbOKOnly, "Device Context Error"
            Exit Sub
         End If

         ' attach the bitmap to the device context just created
         Call SelectObject(lBMDC, hBitmap)

         ' get the information about this image
         Call GetObject(hBitmap, Len(sBitmapInfo), sBitmapInfo)

         ' blit the bitmap image onto the picturebox control
         ' on the form to show what is being worked with
         Call BitBlt(Picture1.hdc, 0, 0, sBitmapInfo.bmWidth, _
                    sBitmapInfo.bmHeight, lBMDC, 0, 0, SRCCOPY)
         Picture1.Refresh

         ' set the timer and turn it on
         Timer1.Interval = 500
         Timer1.Enabled = True

      End Sub

      Private Sub Timer1_Timer()
         Dim hRotatedBitmapDC As Long    ' returned DC to the new bitmap
         Dim lWidth As Long              ' current/new width of the bitmaps
         Dim lHeight As Long             ' current/new width of the bitmaps
         Dim lRadians As Long            ' the degrees will be converted to
                                         ' - radians
         ' get the width/height of the original bitmap image
         lWidth = sBitmapInfo.bmWidth
         lHeight = sBitmapInfo.bmHeight

         ' convert the rotation degrees into radians for the
         ' rotate function
         lRadians = PI * Degrees / 180

         ' set the input var to the current bitmaps DC
         hRotatedBitmapDC = Picture1.hdc

         ' rotate the bitmap to its new degree
         RotateBitmap hRotatedBitmapDC, lWidth, lHeight, lRadians

         ' clear the second picturebox to show the rotated image
         Set Picture2.Picture = LoadPicture

         ' blit the rotated image
         Call BitBlt(Picture2.hdc, 0, 0, lWidth, lHeight, _
                    hRotatedBitmapDC, 0, 0, SRCCOPY)
         Picture2.Refresh

         ' destroy the DC created for the rotated bitmap
         Call DeleteDC(hRotatedBitmapDC)

         ' increase the degree count, or reset if we have come full circle
         Degrees = Degrees + 90
         If Degrees = 360 Then
            Degrees = 0
         End If

      End Sub
  6. In the Form_Load event in the above code, be sure to set the sFileName variable to a bitmap file on your system.
  7. Add the following code to the Standard Module (Module1): 
          Option Explicit

       ' refer to the MSDN for more detailed information regarding the
       ' constants used in this sample.
      Public Const IMAGE_BITMAP = &O0   ' used with LoadImage to load
                                        ' a bitmap
      Public Const LR_LOADFROMFILE = 16    ' used with LoadImage
      Public Const LR_CREATEDIBSECTION = 8192 ' used with LoadImage
      Public Const SRCCOPY = &HCC0020         ' (DWORD) dest = source
      Public Const PI = 3.14159

      ' Refer to the MSDN for more detailed information regarding the
      ' structures used in this sample.
      Type BITMAP '14 bytes
           bmType As Long
           bmWidth As Long
           bmHeight As Long
           bmWidthBytes As Long
           bmPlanes As Integer
           bmBitsPixel As Integer
           bmBits As Long
      End Type

      ' Refer to the MSDN for more detailed information regarding the API's
      ' used in this sample.

      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 CreateCompatibleDC 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 GetObject Lib "gdi32" Alias "GetObjectA" _
         (ByVal hObject As Long, ByVal nCount As Long, lpObject As Any) As
         Long
      Declare Function CreateCompatibleBitmap Lib "gdi32" _
         (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight As Long)
         As Long
      Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long
      Declare Function DeleteObject Lib "gdi32" _
         (ByVal hObject As Long) As Long

      Public Sub RotateBitmap(hBitmapDC As Long, lWidth As Long, _
         lHeight As Long, lRadians As Long)

         Dim hNewBitmapDC As Long    ' DC of the new bitmap
         Dim hNewBitmap As Long      ' handle to the new bitmap
         Dim lSine As Long           ' sine used in rotation
         Dim lCosine As Long         ' cosine used in rotation
         Dim X1 As Long              ' used in calculating new
                                     ' bitmap dimensions
         Dim X2 As Long              ' used in calculating new
                                     ' bitmap dimensions
         Dim X3 As Long              ' used in calculating new
                                     ' bitmap dimensions
         Dim Y1 As Long              ' used in calculating new
                                     ' bitmap dimensions
         Dim Y2 As Long              ' used in calculating new
                                     ' bitmap dimensions
         Dim Y3 As Long              ' used in calculating new
                                     ' bitmap dimensions
         Dim lMinX As Long           ' used in calculating new
                                     ' bitmap dimensions
         Dim lMaxX As Long           ' used in calculating new
                                     ' bitmap dimensions
         Dim lMinY As Long           ' used in calculating new
                                     ' bitmap dimensions
         Dim lMaxY As Long           ' used in calculating new
                                     ' bitmap dimensions
         Dim lNewWidth As Long       ' width of new bitmap
         Dim lNewHeight As Long      ' height of new bitmap
         Dim I As Long               ' loop counter
         Dim J As Long               ' loop counter
         Dim lSourceX As Long        ' x pixel coord we are blitting
                                     ' from the source  image
         Dim lSourceY As Long        ' y pixel coord we are blitting
                                     ' from the source image

         ' create a compatible DC from the one just brought
         ' into this function
         hNewBitmapDC = CreateCompatibleDC(hBitmapDC)

         ' compute the sine/cosinse of the radians used to
         ' rotate this image
         lSine = Sin(lRadians)
         lCosine = Cos(lRadians)

         ' compute the size of the new bitmap being created
         X1 = -lHeight * lSine
         Y1 = lHeight * lCosine
         X2 = lWidth * lCosine - lHeight * lSine
         Y2 = lHeight * lCosine + lWidth * lSine
         X3 = lWidth * lCosine
         Y3 = lWidth * lSine

         ' figure out the max/min size of the new bitmap
         lMinX = Min(0, Min(X1, Min(X2, X3)))
         lMinY = Min(0, Min(Y1, Min(Y2, Y3)))
         lMaxX = Max(X1, Max(X2, X3))
         lMaxY = Max(Y1, Max(Y2, Y3))

         ' set the new bitmap width/height
         lNewWidth = lMaxX - lMinX
         lNewHeight = lMaxY - lMinY

         ' create a new bitmap based upon the new width/height of the
         ' rotated bitmap
         hNewBitmap = CreateCompatibleBitmap _
         (hBitmapDC, lNewWidth, lNewHeight)

         ' attach the new bitmap to the new device context created
         ' above before constructing the rotated bitmap
         Call SelectObject(hNewBitmapDC, hNewBitmap)

         ' loop through and translate each pixel to its new location.
         ' this is using a standard rotation algorithm
         For I = 0 To lNewHeight
            For J = 0 To lNewWidth
               lSourceX = (J + lMinX) * lCosine + (I + lMinY) * lSine
               lSourceY = (I + lMinY) * lCosine - (J + lMinX) * lSine
               If (lSourceX >= 0) And (lSourceX <= lWidth) And _
               (lSourceY >= 0) And (lSourceY <= lHeight) Then
                  Call BitBlt(hNewBitmapDC, J, I, 1, 1, hBitmapDC, _
                              lSourceX, lSourceY, SRCCOPY)
               End If
            Next J
         Next I

         ' reset the new bitmap width and height
         lWidth = lNewWidth
         lHeight = lNewHeight

         ' return the DC to the new bitmap
         hBitmapDC = hNewBitmapDC

         ' destroy the bitmap created
         Call DeleteObject(hNewBitmap)

      End Sub

      Private Function Min(X1 As Long, Y1 As Long) As Long
         If X1 >= Y1 Then
            Min = Y1
         Else
            Min = X1
         End If
      End Function

      Private Function Max(X1 As Long, Y1 As Long) As Long
         If X1 >= Y1 Then
           Max = X1
         Else
            Max = Y1
         End If
      End Function
  8. Press the F5 key to run the project.
Note that the application will load and attempt to read in the bitmap image specified in sFileName. If successful, the image will be blitted to the first PictureBox on the Form. Every half second, the image will then be rotated 90-degrees and blitted into the second PictureBox.
Modification Type:MinorLast Reviewed:7/13/2004
Keywords:kbBitmap kbhowto KB186260
©2004 Microsoft Corporation. All rights reserved.