MFC CreateCompatibleDC(), Drawtext() no display [Solved]

econy

I added a statement:

int nX = tRect.left + tRect.Width() / 2;
int nY = tRect.top + tRect.Height() / 2;
pDC->BitBlt(nX, nY, tRect.Width()/3, tRect.Height()/3, &MemDC,
0, 0, SRCCOPY);

But still get nothing on the screen.

Chris Losinger

you need to create a bitmap for your memdc to draw on. see MSDN dox for CDC::CreateCompatibleDC: http://msdn.microsoft.com/en-us/library/kwxzck32.aspx[^] from the dox:

When a memory device context is created, GDI automatically selects a 1-by-1 monochrome stock bitmap for it. GDI output functions can be used with a memory device context only if a bitmap has been created and selected into that context.

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econy

Thanks, now the test string appeared. But, the client area is black, and show text string in while color only, no change. Please refer to the code:

void CDrawTextTstDlg::OnTimer(UINT_PTR nIDEvent)
{
CDC *pDC;
CRect tRect;
CDC MemDC;

pDC = this->GetDC();
GetClientRect(&tRect);
MemDC.CreateCompatibleDC(NULL);

CBitmap bmp;
bmp.CreateCompatibleBitmap(&MemDC, tRect.Width(), tRect.Height());
CBitmap *oldBitmap = MemDC.SelectObject(&bmp);
MemDC.SetBkMode(TRANSPARENT);

if (gtest == 0 ){
MemDC.SetTextColor(RGB(255,255,255));
MemDC.DrawText(_T("My Test"),&tRect,DT_CENTER|DT_VCENTER|DT_SINGLELINE);
MemDC.SetTextColor(RGB(255,0,0));
MemDC.DrawText(_T("TEST"),&tRect,DT_CENTER|DT_VCENTER|DT_SINGLELINE);
}
else {
MemDC.SetTextColor(RGB(255,255,255));
MemDC.DrawText(_T("TEST"),&tRect,DT_CENTER|DT_VCENTER|DT_SINGLELINE);
MemDC.SetTextColor(RGB(0,150,0));
MemDC.DrawText(_T("My Test"),&tRect,DT_CENTER|DT_VCENTER|DT_SINGLELINE);

}

pDC->BitBlt(0, 0, tRect.Width(), tRect.Height(), &MemDC,
0, 0, SRCCOPY);
m_Seconds++;
m_TimerEcho.Format(_T("%d: Seconds have passed"), m_Seconds);
gtest ^= 1;

MemDC.SelectObject(oldBitmap);
bmp.DeleteObject();
MemDC.DeleteDC();
ReleaseDC(pDC);

CDialog::OnTimer(nIDEvent);
}

Chris Losinger

bmp.CreateCompatibleBitmap(&MemDC, tRect.Width(), tRect.Height());

instead of MemDC there, use the DC that you used as the source for CreateCompatibleDC. when a memory DC is created, it has a 1x1 pixel monochrome bitmap selected into it. if you create a bitmap compatible with that, you'll get a monochrome bitmap. also, if you want a background color, you'll need to fill the bitmap with that color (CDC::FillSolidRect)

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econy

Thank you very much. Now I can see the Text string color is changing. While, the whole dialog screen is black too, some controls, static texts all disappeared. Do I need to redraw all the controls like DrawText() ? and then BitBlt()? The original dialog screen is white.

Chris Losinger

whenever i need to draw on a dialog, i put a static 'frame' control in the place where i want to draw. then i get that control's rectangle and limit my drawing to that rect.

CRect outRect;
m_myDrawingRectControl.GetWindowRect(outRect);
ScreenToClient(outRect);

also, you should only do drawing in your CDialog's OnPaint method. if you need to trigger drawing from a timer, just call CDialog::InvalidateRect() with your control's rectangle (as above). so:

void CDynamicShowTextDlg::OnTimer(UINT nIDEvent)
{
CRect outRect;
m_myDrawingRectControl.GetWindowRect(outRect);
ScreenToClient(outRect);

InvalidateRect(outRect);
}

void CDynamicShowTextDlg::OnPaint()
{
if (IsIconic())
{
...}
else
{
CRect outRect;
m_myDrawingRectControl.GetWindowRect(outRect);
ScreenToClient(outRect);

  CPaintDC dc(this); // device context for painting

  ...

do your drawing here.
use dc as the source for your CreateCompatible* stuff
...
CDialog::OnPaint();
}

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econy

Very very appreciate your help.

econy

And one more question, even I draw in Timer() function, then WM_PAINT also produced to the system,right?

Chris Losinger

right.

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econy

Hi, I wrote snippet code to test. first, I put a Static text in the dialog box, from the resource file:

IDD_ECHOBUTTONEVENT_DIALOG DIALOGEX 0, 0, 320, 200
...
BEGIN
...
LTEXT "Static",IDC_STATIC_TXT1,89,59,98,26
...
END

In Ontimer():

CRect outRect;
CStatic* pTxt1Static;
pTxt1Static = (CStatic*)GetDlgItem(IDC_STATIC_TXT1);
pTxt1Static->GetWindowRect(&outRect);
ScreenToClient(&outRect);
InvalidateRect(&outRect);
UpdateData(FALSE);

In OnPaint():

if (IsIconic()) {
...
}
else
{
CRect outRect;
CStatic* pTxt1Static;
pTxt1Static = (CStatic*)GetDlgItem(IDC_STATIC_TXT1);
pTxt1Static->GetWindowRect(&outRect);
ScreenToClient(&outRect);

CPaintDC dc(pTxt1Static); 
//dc.SetTextColor(RGB(255,255,255));
dc.SetTextColor(RGB(255,0,0));
dc.SetBkMode(TRANSPARENT);
	
dc.DrawText(\_T("My Test"),&outRect,DT\_CENTER|DT\_VCENTER);
	
CDialogEx::OnPaint();

}

But, the string "My Test" 's position is not at same position of Static text(IDC_STATIC_TXT1). offset I guess is about 50 to 100 pixel. And if I change CPaintDC dc(pTxt1Static) to CPaintDC dc(this), I got nothing, even I stretch the dialog box to double, triple size. If I don't use ScreenToClient(&outRect) in OnTimer(), and OnPaint(), I can see "My Test" string, but, need to stretch the dialog; I set break point, pTxt1Static->GetWindowRect(&outRect); give : tagRECT = {top=309 bottom=351 left=577 right=724} run to ScreenToClient(&outRect); give: tagRECT = {top=96 bottom=138 left=134 right=281} Could you please help me to see what is the reason?

Chris Losinger

econy wrote:

But, the string "My Test" 's position is not at same position of Static text(IDC_STATIC_TXT1).
offset I guess is about 50 to 100 pixel.

could that be due to the DT_CENTER|DT_VCENTER flags?

econy wrote:

And if I change CPaintDC dc(pTxt1Static) to CPaintDC dc(this),

it should be CPaintDC dc(this). you're painting the dialog, after all, not the static control. also, try making your static control a 'frame' type, not a static text. something like: CONTROL "",IDC_DRAWING_FRAME,"Static",SS_ETCHEDFRAME,12,199,169,66 that gives you a rectangle with no text in it.

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Chris Losinger

also, it is not essential that you use a static control at all. i use them because having an actual control i can move around in the resource dialog editor makes it easy to do the layout of all the other controls. but, if you just want to draw at an arbitrary rectangle and skip the GetWindowRect/ScreenToClient/etc. stuff , you can certainly do that, too.

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econy

Thank you very much.