View source for StretchBlt

{{VB6}}
===What is StretchBlt?===
StretchBlt is a GDI API that is very similar to [http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/bitmaps_0fzo.asp BitBlt] in its operation, except that it not only copies part of a DC to another DC, but it will also stretch it.

===Simple StretchBlt Use===
The following is a simple example of how to use stretchblt (along with a previous code sample - [[Drawing an image to a DC]]) in order to stretch an image to the form's size.

  Private Sub Form_Paint()
      Dim p As StdPicture
      Dim mDC As Long
      
      Set p = LoadPicture("'''some path'''")
      
      mDC = CreateCompatibleDC(Me.hdc)
      DeleteObject SelectObject(mDC, p.Handle)
      
      StretchBlt _
          Me.hdc, _
          0, 0, _
          ScaleX(Me.ScaleWidth, vbTwips, vbPixels), ScaleY(Me.ScaleHeight, vbTwips, vbPixels), _
          mDC, _
          0, 0, _
          ScaleX(p.Width, vbHimetric, vbPixels), ScaleY(p.Height, vbHimetric, vbPixels), _
          vbSrcCopy
      
      DeleteDC mDC
      
      Set p = Nothing
  End Sub

NOTE: You will need to replace "some path" in the LoadPicture call with an actual image path for this code to work.

===Caveats and refinements of this method===
You may have noticed, while playing with this code, that when you are stretching the image to a size smaller than original, you  begin to get horrible drawing artifacts (especially with photos).  But don't despair!  MS thought of this and included two StretchBlt ''modes'' that eliminate this.  To change the StretchBlt mode for a DC, you have to call SetStretchBltMode with one of the available modes.  The two modes that eliminate this horrid effect are: COLORONCOLOR and HALFTONE.  HALFTONE is higher quality but takes longer.

So here's the code:

  'Put below constants in Genaral -> Declarations
  Private Const HALFTONE As Long = 4
  Private Const COLORONCOLOR As Long = 3
 
  Private Sub Form_Paint()
      Dim p As StdPicture
      Dim mDC As Long
      
      Set p = LoadPicture("'''some path'''")
      
      mDC = CreateCompatibleDC(Me.hdc)
      DeleteObject SelectObject(mDC, p.Handle)
      
      SetStretchBltMode Me.hdc, HALFTONE
      StretchBlt _
          Me.hdc, _
          0, 0, _
          ScaleX(Me.ScaleWidth, vbTwips, vbPixels), ScaleY(Me.ScaleHeight, vbTwips, vbPixels), _
          mDC, _
          0, 0, _
          ScaleX(p.Width, vbHimetric, vbPixels), ScaleY(p.Height, vbHimetric, vbPixels), _
          vbSrcCopy
      
      DeleteDC mDC
      
      Set p = Nothing
  End Sub

===See also===

* {{API link|StretchBlt}}

[[Category:API_Calls]]