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| Title | Use the LoadImage API function to antialias an image and save the result into a file |
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| Description | This example shows how to use the LoadImage API function to antialias an image and save the result into a file in Visual Basic 6. When you use LoadImage to load a picture into a PictureBox, you cannot use the PictureBox's Picture property to save or copy the image. This example shows how to save the picture in a memory bitmap and then use BitBlt to copy it into the PictureBox. |
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| Keywords | antialias, anti-alias, anti alias, alias, LoadImage, resize, LoadPicture, SavePicture |
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| Categories | Graphics, API |
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If you use the LoadIMage API function to load an image into a PictureBox and then you pass the control's Picture property to SavePicture, you get a picture containing the PictureBox's background. I don't know why this is true but here's a workaround.
Rather than assigning the loaded image directly to the PictureBox, the program loads it into a temporary memory context and then uses BitBlt to copy the result into the PictureBox. Setting pic.Picture = pic.Image at the end makes the picture permanent. For example, if you use pic.Cls after this, the picture remains.
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' Use LoadImage to load the picture.
Private Sub LoadWithLoadImage(ByVal pic As PictureBox, _
ByVal file_name As String)
Dim hbm As Long
Dim wid As Long
Dim hgt As Long
Dim temp_dc As Long
' Load the image using LoadImage.
wid = pic.ScaleX(pic.ScaleWidth, pic.ScaleMode, _
vbPixels)
hgt = pic.ScaleY(pic.ScaleHeight, pic.ScaleMode, _
vbPixels)
hbm = LoadImage(ByVal 0&, file_name, _
IMAGE_BITMAP, wid, hgt, LR_LOADFROMFILE)
' Make a device context to hold the picture.
temp_dc = CreateCompatibleDC(0)
SelectObject temp_dc, hbm
' Copy the picture into the PictureBox.
BitBlt pic.hdc, 0, 0, wid, hgt, temp_dc, 0, 0, SRCCOPY
' Delete the DC and bitmap.
DeleteDC temp_dc
DeleteObject hbm
' Make the image permanent.
pic.Picture = pic.Image
End Sub
Private Sub Form_Load()
Dim file_name As String
file_name = App.Path
If Right$(file_name, 1) <> "\" Then file_name = _
file_name & "\"
' Load using LoadPicture.
imgUnaliased.Picture = LoadPicture(file_name & _
"HalfJack2.bmp")
' Load using LoadWithLoadImage.
LoadWithLoadImage picAliased, file_name & _
"HalfJack2.bmp"
' Copy the picture to an Image control.
imgCopy.Picture = picAliased.Picture
' Save the picture into a file.
SavePicture picAliased.Picture, file_name & _
"HalfJack2_small.bmp"
End Sub
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