Question

Is it possible to scale an image proportionately in VB without one of the 3 or 4 built in properties (since they do not work so well)?

What I am referring to is something that you can do in Java like this:

Image newimg = img.getScaledInstance(230, 310,  java.awt.Image.SCALE_SMOOTH);  

In Java the above line seems to work nicely for scaling the dimensions to fit a specified size.

Answer 1

I had a UserControl that I used to accomplish a better quality resize. Here is an extract from it, hopefully you can find it useful.

Private Const STRETCH_ANDSCANS = 1
Private Const STRETCH_DELETESCANS = 3
Private Const STRETCH_HALFTONE = 4
Private Const STRETCH_ORSCANS = 2
Private Const SRCCOPY = &HCC0020

Private Declare Function StretchBlt Lib "gdi32" (ByVal hdc 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 nSrcWidth As Long, _
                                                   ByVal nSrcHeight As Long, _
                                                   ByVal dwRop As Long) _
                                                   As Long

Private Declare Function SetStretchBltMode Lib "gdi32" (ByVal hdc As Long, _
                                                      ByVal nStretchMode As Long) _
                                                      As Long

And it was called like this:

Private Sub UserControl_Paint()

   Dim lSave As Long

   'set the stretchblit mode (saving the previous value)
   lSave = SetStretchBltMode(UserControl.hdc, STRETCH_HALFTONE)

   'perform blit
   Call StretchBlt(UserControl.hdc, 0, 0, UserControl.ScaleWidth, _
                     UserControl.ScaleHeight, picBuffer.hdc, 0, 0, _
                     picBuffer.ScaleWidth, picBuffer.ScaleHeight, SRCCOPY)

   'restore previous mode
   Call SetStretchBltMode(UserControl.hdc, lSave)

End Sub