Drawing on owner draw picture control

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i am converting my code from vb to c++ there are some dynamic points which are there to draw different shapes.

in vb they have properties such as .ScaleWidth, .ScaleHeight, .ScaleTop , .ScaleLeft.

what they had done is they had scaled according to width and height using these properties and draw points(shapes) on the picture box in vb.

but in mfc i have all the input points required but when iam drawing not able to draw properly or correctly. please help me i.e not able to scale properly please help me out.

What I have tried:

void CPDlgToolPreview::S_SetDrawingScale()
{
	short i;
	float lnMaxX;
	float lnMaxY;
	float lnMinX;
	float lnMinY;
	const int BigNumber = 1000000000;
	float lnWidth;
	float lnHeight;

	lnMaxX = (float)(-BigNumber);
	lnMaxY = (float)(-BigNumber);
	lnMinX = (float)(BigNumber);
	lnMinY = (float)(BigNumber);

	for (i = 0; i < mlPoints; i++) 
	{
		if (moPts[i].X > lnMaxX) lnMaxX = (float)(moPts[i].X);
		if (moPts[i].Y > lnMaxY) lnMaxY = (float)(moPts[i].Y);
		if (moPts[i].X < lnMinX) lnMinX = (float)(moPts[i].X);
		if (moPts[i].Y < lnMinY) lnMinY = (float)(moPts[i].Y);
	}

	lnWidth = lnMaxX - lnMinX;
	lnHeight = lnMaxY - lnMinY;

	CRect cRect;
	m_cPreview.GetClientRect(&cRect);
	

	if ( lnWidth / cRect.Width() > lnHeight / cRect.Height() )
	{
		// Scale according to items width	
		nScaleWidth = lnWidth*1.2;
		nScaleHeight = cRect.Height() *nScaleWidth / cRect.Width();
	}
	else
	{
		// Scale according to items height
		 nScaleHeight = lnHeight*1.2;
		 nScaleWidth = cRect.Width() *nScaleHeight / cRect.Height();
	}

	nScaleleft = -nScaleWidth / 2;
	nScaletop = -((nScaleHeight - lnHeight) / 2) - lnHeight;

}

for (short i  = 2; i < mlPoints; i++) 
	{
		DrawLine(m_cPreview, moPts[i].X  , moPts[i].Y);
	}

void DrawLine(CWnd *wnd, int x1, int y1, int x2, int y2, int rgb)
{
CDC *cdc = wnd->GetDC();
CPen *oldPen = cdc->SelectObject(new CPen(0, 3, rgb));
cdc->MoveTo(x1, y1);
cdc->LineTo(nCurrentx = x2, currenty= y2);
delete (CPen *)cdc->SelectObject(oldPen);
wnd->ReleaseDC(cdc);
}

where to use these scaleleft, nScaleHeight etc to get proper shape.

Posted 1-Mar-17 0:37am

Member 12677926

Updated 1-Mar-17 1:06am

v2

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KarstenK · Answer 1 · 2017-03-01T01:06:00

With C++ and MFC you have the power and responsibility to draw each pixel for yourself. For that you must scale what you want to draw in the drawing rectangle.

There are two way:

1. scale the content coordinates before drawing them (recommanded for your DrawLine)
2. draw an offline bitmap and scale that into in the drawing rectangle.

A useful function is Bitblt to draw a scaled bitmap in some step.

When you scale your graphic use one factor, if you use two the might be different and distort the image. Take care that all divisions are made as float and not implicit type conversion is hurding the results.