Understanding GDI mapping modes and other functions

This tool was contributed by Hans Wedemeyer.

MapMode.exe is an interactive tool that can help a programmer better understand various graphics functions and their interactions.

It demonstrates the interactions of

SetMapMode()    // all eight modes
SetWindowExt ()
SetViewportExt ()
SetViewportOrg ()
BitBlt( )

Have you ever wondered what a printed page will look like in a particular map mode, here's thre answer and you don't have to write code to find out !

Ever wondered what all those arguments to BitBlt() do ! now you can find out!

Open eight windows and compare all eight map modes at the same time !

When you run the program, there appears a "control panel", on it are various buttons to adjust the parameters for each function. as you adjust the screen is repainted and the change takes place immediately.

Consider these to be in the program's OnDraw()

void MapMode::OnDraw(CDC* pDC )
    CRect rect;

    if ( pDC->IsPrinting())
        rect.left = 0;
        rect.top = 0;
        rect.right = pDC->GetDeviceCaps(HORZRES);
        rect.bottom = pDC->GetDeviceCaps(VERTRES);

    pDC->SetMapMode ( m_nMapMode );

    pDC->SetWindowExt ( X, Y )

    pDC->SetViewportExt ( X , Y );

    pDC->SetViewportOrg ( X, Y );

    bmp.CreateCompatibleBitmap( pDC, X, Y );

   pDC->BitBlt( X1, Y1, X2, Y2, pBmpDC, X3, Y3, SRCCOPY );

You may draw a line to better understand or locate various x,y coordinates.

Additions made since the original tool.

Annotated origins for easy indentifaction.

Another new feature is "Find Origin" which help pin point in which direction the origin could be, useful if you loose the origin off screen.

Download file


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