GDI Drawing a stupid line!

I have reduced my code to try and simplify my problem.
This snippet from my windows proceedure draws to the screen as expected.

Code:

	case WM_PAINT:	
		{
			hDC = BeginPaint( hwnd, &ps );
			HPEN hPen = CreatePen(PS_SOLID, 1, RGB(255,0,0));
			SelectObject( hDC, hPen );
			MoveToEx(hDC,52,52,NULL);
			LineTo(hDC,100,200);
			DeleteObject( SelectObject( hDC, GetStockObject( BLACK_PEN ) ) );
			ReleaseDC( hwnd, hDC );
			EndPaint( hwnd, &ps );
			return 0;
		}

When I move my code to another function it doesn't draw anything. Here is my most recent attempt to get it up and running:

Code:

void DrawSection(HWND hwnd)
{
	HDC hDC;
	hDC = GetDC( hwnd);
	HPEN hPen = CreatePen(PS_SOLID, 1, RGB(255,0,0));
	SelectObject( hDC, hPen );
	MoveToEx(hDC,0,0,NULL);
	LineTo(hDC,100,200);
	DeleteObject( SelectObject( hDC, GetStockObject( BLACK_PEN ) ) );
	ReleaseDC( hwnd, hDC );
	//	UpdateWindow(hwnd);
	//	InvalidateRect (hwnd, NULL, TRUE);
	//	SendMessage(hwnd,WM_PAINT,0,0);
	return;
}

Nothing wrong with that code, it's something else. Post a sample app with the modified code you're using.

Try making hDC static. it might work.

It is drawing the line in my dialog window I use to get input!

Here is what I had:

Code:

BOOL CALLBACK CircleProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam)
{
	int nLen = 0;
	int Decimal =0;
	LPTSTR pbuffer = NULL;

    switch(Message)
    {
        case WM_INITDIALOG:
			return TRUE;

        case WM_COMMAND:
            switch(LOWORD(wParam))
            {
                case IDOK:
					subsectionData[SectionNumber].sectionType = circle;

					hdlg = GetDlgItem(hwnd, IDC_CIRCLE_DIAMETER);  //(hOwner, hDialogEditField)
					nLen = GetWindowTextLength(hdlg);
					pbuffer = (LPTSTR)malloc(nLen + 1);
					GetDlgItemText(hwnd,	//(hOwner, hDialogEditField)
						IDC_CIRCLE_DIAMETER,	// control identifier
						pbuffer,			// pointer to buffer for text
						nLen+1				// maximum size of string + NULL
					);
					subsectionData[SectionNumber].sectionSpecificData.circleData.diameter 
						= strtod(pbuffer, NULL);
					// Validation...Do not allow a ?zero? or ?negative? number.
					if (subsectionData[SectionNumber].sectionSpecificData.circleData.diameter <= 0)
					{
						MessageBox (NULL, TEXT ("Enter a valid floating point number."), 
							TEXT ("Invalid input!"), MB_ICONINFORMATION) ;
						return TRUE;	// break out of switch statement.
					}

					free(pbuffer);

					DialogBox(GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_CENTER_COORDINATES), 
						hwnd, CenterCoordinates);
					// since this is a circle subsectionData[].ptX and .ptY = .XBAR and .YBAR respectively.
					subsectionData[SectionNumber].XBAR = subsectionData[SectionNumber].ptX[0];
					subsectionData[SectionNumber].YBAR = subsectionData[SectionNumber].ptY[0];

					// Need this here to dismiss CenterCoord dialog before...
					// ...calling another dialog in case user selects cancel.
					EndDialog(hwnd, IDOK);
					
					// Dont call CalculateData... just do calcs here.
					subsectionData[SectionNumber].Ixc = (PI/64)*(pow(subsectionData[SectionNumber].sectionSpecificData.circleData.diameter, 4.0));
					subsectionData[SectionNumber].Iyc = subsectionData[SectionNumber].Ixc;
					subsectionData[SectionNumber].area = PI * pow(subsectionData[SectionNumber].sectionSpecificData.circleData.diameter/2, 2);
					DialogBox(GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_ADD_SUBTRACT_SECTION),
						hwnd, AddSubtractProc);
					EndDialog(hwnd, IDOK);
					TransformationEquation();
					CalculateCompositeData(hwnd);
					SectionNumber++;  //Count of total number of sections.
					bFileNeedsSaved = TRUE;	//Data has been modified needs to be saved.
/**************************************************************/
//					DrawSection(hwnd); // This is where I originally placed it.
/**************************************************************/
				//	SendMessage(hwnd,WM_PAINT,0,0);
					break;
                case IDCANCEL:
					MessageBeep (0) ;
                    EndDialog(hwnd, IDCANCEL);
					break;
            }
			break;
			default:
				return FALSE;
    }
	DrawSection(hwnd); // I placed it here just to see if it would paint and it does but in my 
	// dialog box instead of my main window!
    return TRUE;
}

I moved it into the callback for my window proc. like so:

Code:

case IDM_SECTIONS_CIRCLE:
			 DialogBox(GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_CIRCLE_PROPERTIES), hwnd, CircleProc);
			 DrawSection(hwnd);
			 return 0;

and what do you know it works now.

Try using NULL in the GetDC() (or the HWND to the control or dlg to be redrawn.

I think the line will disappear if the screen is redrawn (use a msgbox to test)

The ReleaseDC() is not needed as EndPaint() does that.

Use
//tell the app where to redraw
InvalidateRect(hWnd,&Area,bBckGrnd);
//ask it to draw this dialog
UpdateWindow(hWnd);

in the paint function use
GetUpdateRect() to only draw the invalidated rect