Invalidaterect

InvalidateRect ()

Im trying to draw a rectangle around an arrow with InvalidateRect(hwnd, lpRect, FALSE)
It compiles without error but it keeps flashing and it invalidates the whole client area not only
the rectangle i want.
I guess the problem must be that InvalidateRect(hwnd, lpRect, FALSE) takes a CONST RECT* for rectangle
coordinates while the RECT structure is only of type RECT.
So i must be doing something wrong.
Thanks for any help.

Code:

#include<windows.h> LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ; int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) { static TCHAR szAppName[] = TEXT ("Invalidaterect") ; HWND hwnd ; MSG msg ; WNDCLASS wndclass ; wndclass.style = CS_HREDRAW | CS_VREDRAW ; wndclass.lpfnWndProc = WndProc ; wndclass.cbClsExtra = 0 ; wndclass.cbWndExtra = 0 ; wndclass.hInstance = hInstance ; wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ; wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ; wndclass.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH) ; wndclass.lpszMenuName = NULL ; wndclass.lpszClassName = szAppName ; if (!RegisterClass (&wndclass)) { return 0 ; } hwnd = CreateWindow (szAppName, // window class name TEXT ("The Hello Program"), // window caption WS_OVERLAPPEDWINDOW, // window style CW_USEDEFAULT, // initial x position CW_USEDEFAULT, // initial y position CW_USEDEFAULT, // initial x size CW_USEDEFAULT, // initial y size NULL, // parent window handle NULL, // window menu handle hInstance, // program instance handle NULL) ; // creation parameters ShowWindow (hwnd, iCmdShow) ; UpdateWindow (hwnd) ; while (GetMessage (&msg, NULL, 0, 0)) { TranslateMessage (&msg) ; DispatchMessage (&msg) ; } return msg.wParam ; } LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) { HDC hdc ; PAINTSTRUCT ps ; RECT rect ; HBRUSH hBrush, hOld ; POINT points [7] = {{20, 50},{180, 50},{180, 20},{230, 70}, {180, 120},{180, 90},{20, 90}}; int cpt = 7 ; CONST RECT* lpRect = 0 ; rect.left = 10; rect.top = 40; rect.right = 200; rect.bottom = 140; switch (message) { case WM_PAINT: hdc = BeginPaint(hwnd, &ps); GetClientRect(hwnd, &rect); hBrush = CreateSolidBrush (RGB(20,170,20)) ; hOld = (HBRUSH) SelectObject (hdc,hBrush) ; InvalidateRect(hwnd, lpRect, FALSE) ; FillRect (hdc, &rect, hBrush) ; hBrush = CreateHatchBrush (HS_FDIAGONAL, RGB(200,170,20)) ; hOld = (HBRUSH) SelectObject (hdc,hBrush) ; Polygon(hdc, points, cpt); SelectObject (hdc,hOld) ; DeleteObject (hBrush) ; EndPaint(hwnd, &ps); return 0 ; case WM_DESTROY: PostQuitMessage (0) ; return 0 ; } return DefWindowProc (hwnd, message, wParam, lParam) ; }

Here's a few ideas for you...

Code:

CONST RECT* lpRect = 0 ; rect.left = 10; rect.top = 40; rect.right = 200; rect.bottom = 140;

in this section, you declare lpRect as 0(NULL), and set values for another rectangle called rect. Then, in the following section:

Code:

GetClientRect(hwnd, &rect); hBrush = CreateSolidBrush (RGB(20,170,20)) ; hOld = (HBRUSH) SelectObject (hdc,hBrush) ; InvalidateRect(hwnd, lpRect, FALSE) ;

you fill rect with values returned by GetClientRect(), making your previous efforts to fill it with values pointless, and then you send lpRect, which is still NULL to InvalidateRect(), which probably defaults to making the entire object referred to by hwnd invalid.

How is it that you've worked out that

Code:

FillRect (hdc, &rect, hBrush);

takes the address of a rect, but haven't realised the same for

Code:

InvalidateRect(hwnd, lpRect, FALSE);

That second param should be &rect, just the same as the first. Both take a pointer to a rect a.k.a LPRECT.

Is this what you're trying to do?

Code:

#include<windows.h> #define ID_TIMER 101 LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ; int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) { static TCHAR szAppName[] = TEXT ("Invalidaterect") ; HWND hwnd ; MSG msg ; WNDCLASS wndclass ; wndclass.style = CS_HREDRAW | CS_VREDRAW ; wndclass.lpfnWndProc = WndProc ; wndclass.cbClsExtra = 0 ; wndclass.cbWndExtra = 0 ; wndclass.hInstance = hInstance ; wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ; wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ; wndclass.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH) ; wndclass.lpszMenuName = NULL ; wndclass.lpszClassName = szAppName ; if (!RegisterClass (&wndclass)) { return 0 ; } hwnd = CreateWindow (szAppName, // window class name TEXT ("The Hello Program"), // window caption WS_OVERLAPPEDWINDOW, // window style CW_USEDEFAULT, // initial x position CW_USEDEFAULT, // initial y position CW_USEDEFAULT, // initial x size CW_USEDEFAULT, // initial y size NULL, // parent window handle NULL, // window menu handle hInstance, // program instance handle NULL) ; // creation parameters ShowWindow (hwnd, iCmdShow) ; UpdateWindow (hwnd) ; while (GetMessage (&msg, NULL, 0, 0)) { TranslateMessage (&msg) ; DispatchMessage (&msg) ; } return msg.wParam ; } LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) { static BOOL bFlipFlop = FALSE ; HDC hdc ; PAINTSTRUCT ps ; RECT rect ; HBRUSH hBrush, brDiagonal; POINT points [7] = {{20, 50},{180, 50},{180, 20},{230, 70}, {180, 120},{180, 90},{20, 90}}; int cpt = 7 ; switch (message) { case WM_CREATE: SetTimer (hwnd, ID_TIMER, 1000, NULL); break; case WM_TIMER : bFlipFlop = !bFlipFlop ; rect.left = 15; rect.top = 15; rect.right = 235; rect.bottom = 125; InvalidateRect (hwnd, &rect, FALSE) ; return 0 ; case WM_PAINT: hdc = BeginPaint(hwnd, &ps); GetClientRect(hwnd, &rect); hBrush = CreateSolidBrush (bFlipFlop ? RGB(255,0,0) : RGB(0,0,255)) ; FillRect (hdc, &rect, hBrush) ; Polygon(hdc, points, cpt); brDiagonal = CreateHatchBrush (bFlipFlop ? HS_FDIAGONAL : HS_BDIAGONAL, bFlipFlop ? RGB(0,0,255) :RGB(255,0,0)) ; SelectObject(hdc, brDiagonal); Polygon(hdc, points, cpt); DeleteObject(brDiagonal); DeleteObject (hBrush) ; EndPaint(hwnd, &ps); return 0 ; case WM_DESTROY: KillTimer (hwnd, ID_TIMER) ; PostQuitMessage (0) ; return 0 ; } return DefWindowProc (hwnd, message, wParam, lParam) ; }

Thank you Elkvis, Malc and Bob for the explanation, i modified the code according it.

Quote:

Originally Posted by BobS0327

Is this what you're trying to do?

Yes, thanks a lot Bob, this is it.
And this is how i imagined it.
It executes as intended but then it starts flickering.
I think the problem is that i cant dereference lpRect like *lpRect, in InvalidateRect(hwnd, *lpRect, FALSE).
When i do it wont compile.
I mean that i should dereference it to get the value instead of the address. Right?
So i dont understand.

But now i study your version of dereferencing.
I dont get it entirely yet.

Code:

#include <windows.h> LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ; int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) { static TCHAR szAppName[] = TEXT ("Invalidaterect") ; HWND hwnd ; MSG msg ; WNDCLASS wndclass ; wndclass.style = CS_HREDRAW | CS_VREDRAW ; wndclass.lpfnWndProc = WndProc ; wndclass.cbClsExtra = 0 ; wndclass.cbWndExtra = 0 ; wndclass.hInstance = hInstance ; wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ; wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ; wndclass.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH) ; wndclass.lpszMenuName = NULL ; wndclass.lpszClassName = szAppName ; if (!RegisterClass (&wndclass)) { return 0 ; } hwnd = CreateWindow (szAppName, // window class name TEXT ("The Hello Program"), // window caption WS_OVERLAPPEDWINDOW, // window style CW_USEDEFAULT, // initial x position CW_USEDEFAULT, // initial y position CW_USEDEFAULT, // initial x size CW_USEDEFAULT, // initial y size NULL, // parent window handle NULL, // window menu handle hInstance, // program instance handle NULL) ; // creation parameters ShowWindow (hwnd, iCmdShow) ; UpdateWindow (hwnd) ; while (GetMessage (&msg, NULL, 0, 0)) { TranslateMessage (&msg) ; DispatchMessage (&msg) ; } return msg.wParam ; } LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) { HDC hdc ; PAINTSTRUCT ps ; RECT rect ; CONST RECT* lpRect ; HBRUSH hBrush, hOld ; POINT points [7] = {{20, 60},{180, 60},{180, 30},{230, 80}, {180, 130},{180, 100},{20, 100}}; int cpt = 7 ; rect.left = 10 ; rect.top = 10 ; rect.right = 250 ; rect.bottom = 160 ; lpRect = &rect ; switch (message) { case WM_PAINT: hdc = BeginPaint(hwnd, &ps) ; hBrush = CreateSolidBrush (RGB(20,10,200)) ; hOld = (HBRUSH) SelectObject (hdc,hBrush) ; InvalidateRect(hwnd, lpRect, FALSE) ; FillRect (hdc, lpRect, hBrush) ; hBrush = CreateHatchBrush (HS_FDIAGONAL, RGB(200,170,20)) ; hOld = (HBRUSH) SelectObject (hdc,hBrush) ; Polygon(hdc, points, cpt); SelectObject (hdc,hOld) ; DeleteObject (hBrush) ; EndPaint(hwnd, &ps); return 0 ; case WM_DESTROY: PostQuitMessage (0) ; return 0 ; } return DefWindowProc (hwnd, message, wParam, lParam) ; }

The reason it is flickering is because you're calling InvalidateRect while you're processing the WM_PAINT message. Calling this function forces another WM_PAINT message to be sent to the window. Finish processing one WM_PAINT message and you've got another WM_PAINT message waiting to be processed. For lack of a better description, you're stuck in a WM_PAINT message loop.

If you try to add more functionality to this app such as adding a menu which displays a dialog box, You'll notice, that at the VERY best, the app runs very jerkily.

Code:

case WM_PAINT: hdc = BeginPaint(hwnd, &ps) ; hBrush = CreateSolidBrush (RGB(20,10,200)) ; hOld = (HBRUSH) SelectObject (hdc,hBrush) ; InvalidateRect(hwnd, lpRect, FALSE) ; FillRect (hdc, lpRect, hBrush) ; hBrush = CreateHatchBrush (HS_FDIAGONAL, RGB(200,170,20)) ; hOld = (HBRUSH) SelectObject (hdc,hBrush) ; Polygon(hdc, points, cpt); SelectObject (hdc,hOld) ; DeleteObject (hBrush) ; EndPaint(hwnd, &ps); return 0 ;

Of course, InvalidateRect calls WM_PAINT! Plus i knew that before. Just forgot about it.
Thanks for refreshing my memory.

One more thing that i dont understand is when you call GetClientRect you change the values of rect to the values of the clientarea.
So how come that FillRect fills up the little rectangle then?
And if i dont call GetClientRect, it wont even draw the little rectangle. Its confusing.

Code:

case WM_PAINT: hdc = BeginPaint(hwnd, &ps); GetClientRect(hwnd, &rect); hBrush = CreateSolidBrush (bFlipFlop ? RGB(255,0,0) : RGB(0,0,255)) ; FillRect (hdc, &rect, hBrush) ; Polygon(hdc, points, cpt); brDiagonal = CreateHatchBrush (bFlipFlop ? HS_FDIAGONAL : HS_BDIAGONAL, bFlipFlop ? RGB(0,0,255) :RGB(255,0,0)) ; SelectObject(hdc, brDiagonal); Polygon(hdc, points, cpt); DeleteObject(brDiagonal); DeleteObject (hBrush) ; EndPaint(hwnd, &ps); return 0 ;

Many Windows API functions take a pointer to a RECT. In some cases they do this because the RECT is effectively an out parameter. In other places it is passed by pointer because that is more efficient. In all cases though, you must simply define a RECT, and pass the address of it. You never declare an LPRECT for any of them.

Before calling GetClientRect, your rect probably has coordinates of all zeros, so if you try and do a FillRect with that, you'll get nothing.
After calling it, you'll have the rect coordinates set to that of the window, and you can then pass those coords to FillRect and it will paint the window for you.

In other words, treat InvalidateRect just like FillRect.

Thank you iMalc! Duly noted.

A better tip for you:
The documentation says what arguments it expects and if it's information IN or OUT.
The windows headers also uses these evil pointer typedefs, which might make it somewhat unclear that it is indeed pointers to something it expects, and not some alien type.
Everything that begins with "LP" means basically, it's a pointer of the preceding type.
So LPRECT basically means RECT*.
Some functions also take CONST SOMETHING. CONST is just another upper-case define/typedef for the keyword const which tells the compiler the argument passed to the function will not, shall not, be modified or changed.

To get the address of something, you prefix &. Prefix & to T and you get T*.
Prefix * to dereference a pointer. Prefix * to T* and you get T.
It is important to know this. The functions expect the address of a struct to access its information. You can't just define a pointer and dereference it. What do you think that will accomplish or do?

And in the future, indent your code properly before posting it.

Quote:

The functions expect the address of a struct to access its information.

Thank you Elysia. That makes it clear to understand.