topic Re: Why does GetDC fail? in Intel® Fortran Compiler

Why does GetDC fail?

brianreinhold — Sat, 31 May 2025 15:11:55 GMT

I have this simple routine to draw a solid color box in the client area of a window:

MODULE PboxModule CONTAINS !> This subroutine draws a solid color box in a window. !> It uses the Win32 API to create a filled rectangle !> based on the provided coordinates and RGB color. !! !! @param IX1 Upper-left X-coordinate in window !! @param IY1 Upper-left Y-coordinate in window !! @param IX2 Lower-right X-coordinate in window !! @param IY2 Lower-right Y-coordinate in window !! @param color Packed RGB color value !! @param hWnd Window handle SUBROUTINE PBOX(IX1, IY1, IX2, IY2, color, hWnd) USE IFWIN use user32 use win32Interfaces IMPLICIT NONE ! Declare variables INTEGER, INTENT(IN) :: IX1, IY1, IX2, IY2 INTEGER*4 :: color ! RGB color value. Must be 32-bit INTEGER(HANDLE), INTENT(IN) :: hWnd INTEGER(HANDLE) :: hDC, hBrush INTEGER(BOOL) :: bret integer :: iret, err ! Get the device context for the window hDC = GetDC(hWnd) err = GetLastError() IF (hDC /= 0) THEN ! IC already represents an RGB color hBrush = CreateSolidBrush(color) ! Select the brush into the DC bret = SelectObject(hDC, hBrush) ! Draw the filled rectangle bret = Rectangle(hDC, IX1, IY1, IX2, IY2) ! Cleanup: release device context and delete brush iret = ReleaseDC(hWnd, hDC) iret = DeleteObject(hBrush) END IF END SUBROUTINE PBOX end module PboxModule

However, using the debugger I see the hDC = GetDC(hwnd) returns an absurd value, sometimes positive and sometime negative but in all cases very large. GetLastError() returns 0, but I don't know if that helps for these methods. The handle is valid.

Any ideas what might be wrong?

Re: Why does GetDC fail?

andrew_4619 — Sat, 31 May 2025 21:03:41 GMT

Fortran does not have unsigned integer type so when the high bit is set is show as a negative. The hDC is a memory address and will usually be a large number. Why do you think it is wrong? The info you have posted suggests all is good.

Re: Why does GetDC fail?

brianreinhold — Sat, 31 May 2025 22:54:21 GMT

Because the box does not get drawn in the window. I pass in ix1, iy1 = 10, 10 and ix2, iy2 = 1000, 500 and RGB color red (255). Stepping through the debugger I see that the window handle is valid. I figured SOMETHING must be wrong because the window client area remains untouched after the call to Rectangle. I admit, looking at the responses it suggests that everything succeeded but I see nothing on the screen. Did I forget something stupid?

Intel advertises that it has win32 fortran examples

Sample SDI and MDI Fortran Windows Samples in the WIN32 folder, such as Generic, Platform, or Angle.

But I cannot find them anywhere. Would you know where they are?

Re: Why does GetDC fail?

andrew_4619 — Sun, 01 Jun 2025 10:52:31 GMT

The old samples are well hidden and hard to find, I just happened to do that a few weeks back.....

https://community.intel.com/t5/Intel-Fortran-Compiler/Intel-Fortran-Compiler-Information-and-Frequently-Asked/m-p/1329533#M158339

On that page go to the Product Information sections and there is a sample link that download a zip file.

Re: Why does GetDC fail?

andrew_4619 — Sun, 01 Jun 2025 11:01:01 GMT

What are the returns of CreateSolidBrush, SelectObject and Rectangle? Does the window get a WM_PAINT in the message loop?

Re: Why does GetDC fail?

GVautier — Sun, 01 Jun 2025 12:07:06 GMT

If this function is not called inside a WM_PAINT message I think you need at least a call to updatewindow to force a WM_PAINT to be sent, eventually preceded by a call to invalidaterect if necessary.

Re: Why does GetDC fail?

brianreinhold — Sun, 01 Jun 2025 14:15:34 GMT

@andrew_4619 @GVautier Thanks you guys for helping out. I would have never found those samples. In any case, I have extended my application to error check everything, get the hDC, and get window from hDC. I have added a PEN (and since removed). In all cases everything works EXCEPT rectangle. It always fails with error 6. My updated code (just tons of error checks that print results to a list box in the main dialog) is posted below. However, what might be conflicting is what 'Rectangle' is declared as in the intel library.

The only thing I found is

INTERFACE FUNCTION RECTANGLE(CONTROL,X1,Y1,X2,Y2) !DEC$ ATTRIBUTES DEFAULT :: RECTANGLE INTEGER*2 RECTANGLE !DEC$ ATTRIBUTES DECORATE,C,ALIAS:"_rectangle" :: RECTANGLE INTEGER*2 CONTROL,X1,Y1,X2,Y2 END FUNCTION END INTERFACE INTERFACE FUNCTION RECTANGLE_W(CONTROL,WX1,WY1,WX2,WY2) !DEC$ ATTRIBUTES DEFAULT :: RECTANGLE_W INTEGER*2 RECTANGLE_W,CONTROL !DEC$ ATTRIBUTES DECORATE,C,ALIAS:"_rectangle_w" :: RECTANGLE_W DOUBLE PRECISION WX1,WY1,WX2,WY2 END FUNCTION END INTERFACE INTERFACE

in the file ifqwin.f90. It does NOT seem to be the same as the Rectangle win32 API used in C/C++.

Here is my updated code (unchanged except for error checks)

SUBROUTINE PBOX(IX1, IY1, IX2, IY2, color, hWnd, hLog) USE IFWIN use user32 use gdi32 use win32Interfaces IMPLICIT NONE ! Declare variables INTEGER, INTENT(IN) :: IX1, IY1, IX2, IY2 INTEGER*4, intent(in) :: color ! RGB color value. Must be 32-bit INTEGER(HANDLE), INTENT(IN) :: hWnd, hLog INTEGER(HANDLE) :: hDC, hBrush, hWndCheck INTEGER(BOOL) :: bret integer :: iret character(len=512) :: message type(T_LOGBRUSH) :: logBrush ! Get the device context for the window hDC = GetDC(hWnd) hWndCheck = WindowFromDC(hDC) if (hWndCheck == 0) THEN bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM("Obtained hDC is invalid:"C))) RETURN END IF IF (hDC /= 0) THEN write(message, '(A, I0)') 'hDC Value: ', hDC bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM(message))) ! color already represents an RGB color hBrush = CreateSolidBrush(color) !hBrush = GetStockObject(BLACK_BRUSH) if (hBrush == 0) THEN bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM("Error Creating hBrush:"C))) ELSE message = repeat('', len(message)) write(message, '(A, I0)') 'hBrush value: ', hBrush bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM(message)// CHAR(0))) END IF ! Select the brush into the DC bret = SelectObject(hDC, hBrush) if (bret == 0) THEN bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM("Error Selecting hBrush:"C))) END IF iret = GetObject(hBrush, sizeof(logBrush), LOC(logBrush)) if (iret == 0) THEN iret = ReleaseDC(hWnd, hDC) bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM("Error getting object from hBrush:"C))) RETURN END IF ! Draw the filled rectangle message = repeat('', len(message)) write(message, '(A, I0, A, I0)') 'Drawing rectangle at: ', IX1, ', ', IY1 bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM(message)// CHAR(0))) bret = Rectangle(hDC, IX1, IY1, IX2, IY2) if (bret == 0) THEN iret = GetLastError() message = repeat('', len(message)) write(message, '(A, I0)') 'Drawing rectangle failed with error: ', iret bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM(message)// CHAR(0))) END IF ! Cleanup: release device context and delete brush iret = ReleaseDC(hWnd, hDC) iret = DeleteObject(hBrush) else bret = SendMessage(hLog, LB_ADDSTRING, 0, LOC(TRIM("Error getting device context:"C))) END IF END SUBROUTINE PBOX end module PboxModule

Running it shows that everything works EXCEPT for Rectangle. Window handles are valid (test window is WS_OVERLAPPEDWINDOW), the hDC and hBrush are valid. The error message '6' invalid handle may be very misleading if Rectangle is calling the interface specified above.

By the way, why don't I get an email notification when someone responds here? I have checked that option but it does not happen.

Re: Why does GetDC fail?

brianreinhold — Sun, 01 Jun 2025 14:50:38 GMT

I found the answer and I do not like it at all. First, I found the actual intel reference to the function in gdi32.f90:

FUNCTION MSFWIN$Rectangle( & arg1, & arg2, & arg3, & arg4, & arg5) use ifwinty integer(BOOL) :: MSFWIN$Rectangle ! BOOL !DEC$ ATTRIBUTES DEFAULT, STDCALL, DECORATE, ALIAS:'Rectangle' :: MSFWIN$Rectangle integer(HANDLE) arg1 ! HDC arg1 integer(SINT) arg2 ! int arg2 integer(SINT) arg3 ! int arg3 integer(SINT) arg4 ! int arg4 integer(SINT) arg5 ! int arg5 END FUNCTION END INTERFACE

But I could NOT use

Rectangle(hDC, ix1, iy1, ix2, iy2).

I had to use

MSFWIN$Rectangle(hDC, ix1, iy1, ix2, iy2).

Then it worked. I have absolutely NO idea why I could not use the alias (and so far the alias has worked fine everywhere else)

Re: Why does GetDC fail?

andrew_4619 — Sun, 01 Jun 2025 15:43:53 GMT

I think you have most of the answer I read your earlier post and was about to give you what you have found. In the history Intel supported migration from Microsoft Fortran which ceased in the early 90s, the Microsoft product has a load of graphics routines which later conflicted with the names of windows sdk routines. There is/was am IFWIN module that aliases the names. BTW IFWIN includes GDI32 and USER32 you shout not need to USE those directly

Re: Why does GetDC fail?

andrew_4619 — Sun, 01 Jun 2025 15:52:55 GMT

IFQWIN has a "rectangle"

Re: Why does GetDC fail?

GVautier — Sun, 01 Jun 2025 16:10:29 GMT

Here https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2025-0/rectangle-rectangle-w.html

It's a quickwin function.This kind of problem is hard to solve.

Re: Why does GetDC fail?

andrew_4619 — Sun, 01 Jun 2025 20:59:44 GMT

https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-rectangle

BOOL Rectangle( [in] HDC hdc, [in] int left, [in] int top, [in] int right, [in] int bottom );

That is the SDK version which is what you wanted, you would need to add your own interface. Noting the "int" is a 4 byte integer. the interface below is 32 and 64 bit and would work with ifort/ifx/gfortran

interface ! Recatangle function Rectangle( hdc, left, top,right, bottom) BIND(C,NAME="Rectangle") import integer(BOOL) :: Rectangle ! BOOL !DIR$ ATTRIBUTES STDCALL :: Rectangle !GCC$ ATTRIBUTES STDCALL :: Rectangle integer(HANDLE), value :: hdc ! HDC arg1 integer(SINT), value ::left, top,right, bottom end function end interface

Re: Why does GetDC fail?

brianreinhold — Tue, 03 Jun 2025 12:48:38 GMT

In the end I am just going with the prefixed version of the method. As it turns out I need to use the prefixed version of many methods in gdi32. As long as I know and have it written in the code comments.

Re: Why does GetDC fail?

andrew_4619 — Tue, 03 Jun 2025 14:26:48 GMT

If you are doing that I personally would make a wapper functions e.g. my_rectangle that calls the msfwin and make a module with them all in. That way if you change compiler you only have that module to fix.