The StretchBlt function copies a bitmap from a source rectangle into a destination rectangle, stretching or compressing the bitmap to fit the dimensions of the destination rectangle, if necessary. The system stretches or compresses the bitmap according to the stretching mode currently set in the destination device context.

C# Signature:

The last argument uint dwRop from the signature above specifies a raster operation code defined in the header. A value from enum TernaryRasterOperations below can be used as the last argument to fake the defined value from this signature:

public enum StretchMode
{
     STRETCH_ANDSCANS    =1,
     STRETCH_ORSCANS     =2,
     STRETCH_DELETESCANS =3,
     STRETCH_HALFTONE    =4,
}

User-Defined Types:

public enum TernaryRasterOperations
{
    SRCCOPY     = 0x00CC0020, /* dest = source*/
    SRCPAINT    = 0x00EE0086, /* dest = source OR dest*/
    SRCAND      = 0x008800C6, /* dest = source AND dest*/
    SRCINVERT   = 0x00660046, /* dest = source XOR dest*/
    SRCERASE    = 0x00440328, /* dest = source AND (NOT dest )*/
    NOTSRCCOPY  = 0x00330008, /* dest = (NOT source)*/
    NOTSRCERASE = 0x001100A6, /* dest = (NOT src) AND (NOT dest) */
    MERGECOPY   = 0x00C000CA, /* dest = (source AND pattern)*/
    MERGEPAINT  = 0x00BB0226, /* dest = (NOT source) OR dest*/
    PATCOPY     = 0x00F00021, /* dest = pattern*/
    PATPAINT    = 0x00FB0A09, /* dest = DPSnoo*/
    PATINVERT   = 0x005A0049, /* dest = pattern XOR dest*/
    DSTINVERT   = 0x00550009, /* dest = (NOT dest)*/
    BLACKNESS   = 0x00000042, /* dest = BLACK*/
    WHITENESS   = 0x00FF0062, /* dest = WHITE*/
};

Notes:

StretchBlt can be used to create zoom functionality.

Tips & Tricks:

Please add some!

Sample Code:

Performs a simple zoom on an Hbitmap (hbmp)

[DllImport("gdi32.dll")]
static extern bool StretchBlt(IntPtr hdcDest, int nXOriginDest,
     int nYOriginDest, int nWidthDest, int nHeightDest, IntPtr hdcSrc,
     int nXOriginSrc, int nYOriginSrc, int nWidthSrc, int nHeightSrc,
     TernaryRasterOperations dwRop );

[DllImport("gdi32.dll", ExactSpelling=true, SetLastError=true)]
static extern IntPtr CreateCompatibleDC(IntPtr hdc);

[DllImport("gdi32.dll", ExactSpelling=true, SetLastError=true)]
static extern bool DeleteDC(IntPtr hdc);

[DllImport("gdi32.dll", ExactSpelling=true, SetLastError=true)]
static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);

[DllImport("gdi32.dll", ExactSpelling=true, SetLastError=true)]
static extern bool DeleteObject(IntPtr hObject);

public enum TernaryRasterOperations
{
     SRCCOPY     = 0x00CC0020, /* dest = source*/
     SRCPAINT    = 0x00EE0086, /* dest = source OR dest*/
     SRCAND      = 0x008800C6, /* dest = source AND dest*/
     SRCINVERT   = 0x00660046, /* dest = source XOR dest*/
     SRCERASE    = 0x00440328, /* dest = source AND (NOT dest )*/
     NOTSRCCOPY  = 0x00330008, /* dest = (NOT source)*/
     NOTSRCERASE = 0x001100A6, /* dest = (NOT src) AND (NOT dest) */
     MERGECOPY   = 0x00C000CA, /* dest = (source AND pattern)*/
     MERGEPAINT  = 0x00BB0226, /* dest = (NOT source) OR dest*/
     PATCOPY     = 0x00F00021, /* dest = pattern*/
     PATPAINT    = 0x00FB0A09, /* dest = DPSnoo*/
     PATINVERT   = 0x005A0049, /* dest = pattern XOR dest*/
     DSTINVERT   = 0x00550009, /* dest = (NOT dest)*/
     BLACKNESS   = 0x00000042, /* dest = BLACK*/
     WHITENESS   = 0x00FF0062, /* dest = WHITE*/
};

protected override void OnPaint(PaintEventArgs e)
{
    IntPtr pTarget = e.Graphics.GetHdc();
    IntPtr pSource = CreateCompatibleDC(pTarget);
    IntPtr pOrig = SelectObject(pSource, hbmp);
    StretchBlt(pTarget, 0, 0, bmp.Width * 2, bmp.Height * 2,pSource,
        0,0,bmp.Width,  bmp.Height,TernaryRasterOperations.SRCCOPY);
    IntPtr pNew = SelectObject(pSource, pOrig);
    DeleteObject(pNew);
    DeleteDC(pSource);
    e.Graphics.ReleaseHdc(pTarget);
}

To Zoom out using StretchBlt use SetStretchBltMode() before calling StretchBlt()

protected override void OnPaint(PaintEventArgs e)
{
    IntPtr pTarget = e.Graphics.GetHdc();
    IntPtr pSource = CreateCompatibleDC(pTarget);
    IntPtr pOrig = SelectObject(pSource, hbmp);
    SetStretchBltMode(pTarget, StretchMode.STRETCH_DELETESCANS);
    StretchBlt(pTarget, 0, 0, width/2, height/2,pSource, 0,0,bmp.Width,
        bmp.Height,TernaryRasterOperations.SRCCOPY);
    IntPtr pNew = SelectObject(pSource, pOrig);
    DeleteObject(pNew);
    DeleteDC(pSource);
    e.Graphics.ReleaseHdc(pTarget);
}

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Documentation

StretchBlt on MSDN

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