Difference between revisions of "StretchBlt"
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===What is StretchBlt?=== | ===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. | 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=== | ===Simple StretchBlt Use=== | ||
| − | The following is a simple example of how to use stretchblt (along with a previous code sample - [ | + | 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() | Private Sub Form_Paint() | ||
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So here's the code: | 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() | Private Sub Form_Paint() | ||
Dim p As StdPicture | Dim p As StdPicture | ||
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Set p = Nothing | Set p = Nothing | ||
End Sub | End Sub | ||
| + | |||
| + | ===See also=== | ||
| + | |||
| + | * {{API link|StretchBlt}} | ||
| + | |||
| + | [[Category:API_Calls]] | ||
Latest revision as of 10:28, 20 November 2006
| This article is based on Visual Basic 6. Find other Visual Basic 6 articles. |
Contents
What is StretchBlt?
StretchBlt is a GDI API that is very similar to 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
