HOWTO: Rotate a Bitmap Image in 90-Degree Increments
ID: Q186260
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The information in this article applies to:
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Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0
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
- Create a new Standard EXE project in Visual Basic. Form1 is created
by default.
- Add a Standard Module (Module1) to the project.
- Add the following controls to Form1:
- Two PictureBox controls
- One Timer control
- For the two PictureBox controls, set their AutoRedraw properties to
True.
- 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
- In the Form_Load event in the above code, be sure to set the sFileName
variable to a bitmap file on your system.
- 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
- 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.
Additional query words:
sprites animation kbDSupport kbdss kbBitMap kbVBp500 kbVBp600 kbVBp
Keywords : kbGrpVB
Version :
Platform : WINDOWS
Issue type : kbhowto
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