Simple Magnifier Dialog

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Introduction

Writing graphics processing software has occupied a substantial part of my engineering work. I find it to be enjoyable work. Frequently, I need to amplify pixels painted on the screen. There are magnifiers available, and I have used some with satisfying results. But I wanted a small enough object that I could re-use on my other applications, one over which I would have a bit more control.

The second reason for my desire to write this code is trying to use CMemdDC, by Keith Rule, in a dialog. I have previously used CMemDC on a CScrollView::OnDraw() with great results. Using it on a dialog presented a bit of a problem, one that I could not solve at the time, and had left this work for another day.

The third reason is that I wanted to use a modeless dialog from within a View environment. Since I had not used this mechanism before, this seemed a good place to investigate.

Most importantly, I thought this would be a fun project to undertake.

CMagnifierDlg

The operation of the magnifier resides on a modeless dialog, a class I have named CMagnifierDlg.

CMagnifierDlg magnifies a portion of the graph by drawing the representation of one pixel into a rectangle, a "cell." The larger the cell, the higher the magnification. A combination of a group of cells is placed in a control within the dialog. The dialog allows to zoom in by simply displaying larger cells for each pixel.

Since this process will reside on a modeless dialog, I modified the dialog in two ways:

1. Eliminating the "OK" and "Cancel" buttons on the dialog.
2. On the "OnCancel" function, I placed a call to ShowWindow(SW_HIDE); to put it out of the way yet ready to be recalled again.

When the user needs to re-activate the magnifier, CScrollView calls m_MagnifierDlg.ShowWindow(SW_SHOW);

When the user clicks on the observed window surface, CMagnifierAppView places a call to the dialog, m_MagnifierDlg.vSetMagnificationPoint(); indicating the new location to enlarge.

Using the Code

In the CSrollView class, I instantiated a CMagnifierDlg object. The dialog will not be operational until you "create" it. When the user clicks on the magnifier button, the code "creates" the dialog, makes a call to the dialog to Create();, and now the dialog comes to life. From then on, the CScrollView will need to communicate the magnifier the location the user has clicked, for a new magnification display.

//
// Magnifier AppView.h
class CMagnifierAppView : public CScrollView
{
…
CMagnifierDlg m_MagnifierDlg;
…
};

//
// Magnifier AppView.cpp 
void CMagnifierAppView::OnButtonEmbeddedDialog() 
{
	if (!m_MagnifierDlg.bDialogWasCreated())
    {
		m_MagnifierDlg.Create(this);
	}
	else
	{
		m_MagnifierDlg.ShowWindow(SW_SHOW);
	}
}

void CMagnifierAppView::OnInitialUpdate() 
{
	CMagnifierAppDoc* pDoc = GetDocument();
	CScrollView::OnInitialUpdate();
	
	CString csFilePath = pDoc->GetPathName();
	if (!csFilePath.IsEmpty())
	{
		if (bReadBMPFile(csFilePath))
			SetScrollSizes( MM_TEXT, CSize(m_bih.biWidth, m_bih.biHeight));
	}
	else
	{
	   SetScrollSizes( MM_TEXT, CSize( 1, 1 ) );
	}

    InvalidateRect(NULL);
}

void CMagnifierAppView::OnLButtonDown(UINT nFlags, CPoint point) 
{
	CPoint ptUserClicked = point;
	ptUserClicked.x += GetScrollPos(SB_HORZ);
	ptUserClicked.y += GetScrollPos(SB_VERT);
	m_MagnifierDlg.vSetMagnificationPoint(ptUserClicked);
	
	CScrollView::OnLButtonDown(nFlags, point);
}

The function bool CMagnifierAppView::bReadBMPFile(…) loads the data into a memory buffer from where to paint the graph.

Conclusion and Points of Interest

In this sample, we have shown a simple way to create a magnification of a graph. We have used CMemDC on a dialog, a modeless dialog and we have instantiated the modeless dialog on a CScrollView.

History

• 8^th June, 2020: Initial version