Views Topics: Displaying a Bitmap

	Views Topics: Displaying a Bitmap

Introduction

Displaying a bitmap in a CView or CScrollView-based application can be fairly easy if you are using a bitmap created as a resource. What makes this easy is that you already know what picture the user would use and you may have provided only a (limited) set of pictures. In some applications, you may want to let the user select the picture to display. To do this, you would use a File Dialog that allows the user to select a picture as a file and them you can display it.

Practical Learning: Displaying a Bitmap in a View

Start Microsoft Visual C++ and create an MFC Application named ShowPicture1
Create it as a Single Document
Base the view class on CScrollView and click Finish
In the Class View, right-click the name of the view class -> Add -> Add Variable...
Create a private CString variable named strFilename and click Finish
In the Resource View, double-click the IDR_MAINFRAME menu
Right the Open menu item and click Add Event Handler...
In the Class List, select the view class
Click Add and Edit

Implement the event as follows:

void CShowPicture1View::OnFileOpen()
{
	// TODO: Add your command handler code here
	TCHAR strFilter[] = { TEXT("Picture Files (*.bmp)|*.bmp||") };
	CFileDialog dlg(TRUE, TEXT(".bmp"), NULL, 0, strFilter);

	if( dlg.DoModal() == IDOK )
	{
		strFilename = dlg.GetFileName();
		Invalidate();
	}
}

Access the OnDraw event (of the view class) and change its as follows:

void CShowPicture1View::OnDraw(CDC* pDC)
{
	CShowPicture1Doc* pDoc = GetDocument();
	ASSERT_VALID(pDoc);
	if (!pDoc)
		return;

	// TODO: add draw code for native data here
	if( strFilename != "" )
	{
		BITMAP bmpProperties;

		// Create a bitmap handle using the name of the file
		HBITMAP bmpHandle = (HBITMAP)LoadImage(NULL,
			                               strFilename,
					               IMAGE_BITMAP,
					               0,
						       0,
						       LR_LOADFROMFILE);

		CBitmap bmpPicture;
		CDC mdcPicture;

	// Convert the Win32 bitmap handle into an MFC bitmap object
		CBitmap *bmpFromHandle = bmpPicture.FromHandle(bmpHandle);
		bmpPicture.Attach(bmpHandle);

	// Call the Win32 GetObject() function to get the properties
		// of the bitmap and store them in a BITMAP structure
		::GetObject(bmpPicture,
			    sizeof(bmpProperties),
			    &bmpProperties);

		// Create a compatible device context
		mdcPicture.CreateCompatibleDC(pDC);
		// Select the bitmap into the device context
		CBitmap * bmpPrevious = 
				mdcPicture.SelectObject(bmpFromHandle);

		// Using the dimensions store in the BITMAP object,
		// display the picture
		pDC->BitBlt(0, 0,
			    bmpProperties.bmWidth, bmpProperties.bmHeight,
			    &mdcPicture, 0, 0, SRCCOPY);

		// Get the dimensions of the new picture
		SIZE sizeTotal;
		sizeTotal.cx = bmpProperties.bmWidth;
		sizeTotal.cy = bmpProperties.bmHeight;
		// Change the scrolling area/dimensions of the view
		SetScrollSizes(MM_TEXT, sizeTotal);

		// Restore the bitmap
		pDC->SelectObject(bmpPrevious);
		// Delete the Win32 bitmap handle
		DeleteObject(bmpHandle);
	}
}

Execute the application
Close the application