C++ WinApi Fillrect() crashes (multiple rects) - c++

Question

i am trying to get used to WinApi and decided to make a GUI for a sudoku-generator i programmed.
It should adjust dynamicly to the windowsize the user chooses.
So far everything works as inteded, but if the WM_PAINT-msg is sent too often in a short window of time (eg changing the size of the window) the program crashes.
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
HDC hdc;
PAINTSTRUCT ps;
stringstream ss; //not used
RECT rect;
int w;
int h;
HBRUSH coluns=CreateSolidBrush(RGB(50,120,180));
HBRUSH colsel=CreateSolidBrush(RGB(80,150,220));
HBRUSH colmso=CreateSolidBrush(RGB(50,70,190));
switch (message)
{
case WM_SIZE: //
{
GetWindowRect(hwnd,&rect);
menu.wndw=rect.right-rect.left; //menu is a class to store important information
menu.wndh=rect.bottom-rect.top;
h=menu.wndh;
w=menu.wndw;
for(int i=1;i<10;i++)
{
for(int j=1;j<10;j++)
{
menu.feld[i][j].SetSpace((w/4)+((i-1)*(w/20))+i+(2*((i-1)/3)),(h/4)+((j-1)*(h/20))+j+(2*((j-1)/3)),(w/4)+((i)*(w/20))+i+(2*((i-1)/3)),(h/4)+((j)*(h/20))+j+(2*((j-1)/3)));
}
} //feld is a class wich exists in a 10x10 array with the 0s not being used
InvalidateRect(hwnd,NULL, TRUE);
}
break;
case WM_PAINT:
{
RECT re;
w=menu.wndw;
h=menu.wndh;
hdc = BeginPaint(hwnd,&ps);
re.left=(w/4)-4;
re.top=(h/4)-4;
re.right=(w/4)+9*(w/20)+18;
re.bottom=(h/4)+9*(h/20)+18;
FillRect(hdc,&re,CreateSolidBrush(RGB(0,0,0)));
for(int i=1;i<10;i++)
{
for(int j=1;j<10;j++)
{
re=menu.feld[i][j].GetSpace();
if(menu.feld[i][j].GetSelect()==uns)
if(FillRect(hdc,&re,coluns)==0)
MessageBox(hwnd, "fail","fail",0);
if(menu.feld[i][j].GetSelect()==mso)
if(FillRect(hdc,&re,colmso)==0)
MessageBox(hwnd, "fail","fail",0);
if(menu.feld[i][j].GetSelect()==sel)
if(FillRect(hdc,&re,colsel)==0)
MessageBox(hwnd, "fail","fail",0);
}
}
EndPaint(hwnd, &ps);
}
break;
http://www.pic-upload.de/view-22113118/Unbenannt.png.html
here is a picture of what the executed program looks like.
Now as described earlier the program will crash if u change the windowsize in a lot of small steps. After calling the MW_PAINT msg for ~10 times the window will just freeze with 1 of the rects being white instead of the desired color (random one, different every time).
my assumption is that i need to release some kind of resources because mby a stack will overflow or smth, but i have really no idea where i could have a leak in my program.
i would be very grateful if anyone could help me.

Answer 1

You create three brush handles every single time your window procedure executes. These handles are never tidied up. And then inside the WM_PAINT handler, you create a brush which you pass to FillRect and so can never destroy it.
So you leak three handles every time the window procedure executes (which happens a lot), and one more every time it handles WM_PAINT. Simply put, your program leaks like a sieve!
You should consider creating these brushes when the window is created, and destroying them when the window is destroyed. Or perhaps creating them inside the WM_PAINT handler, and destroying them as soon as you have finished using them. But since they have constant colors it is probably best to create 4 brushes up front, once and for all.

Answer 2

You are leaking GDI resources as member David Heffernan said.
Here is the example of how to properly use brushes in your application-pay attention to WM_COMMAND handler in that example.
If you do not use stock GDI objects you must delete them after you are done working with them.
Here is the simple example that fills window with red brush in WM_PAINT handler:
case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPain( hdc, &ps );
HBRUSH hbrRedBrush = CreateSolidBrush( RGB( 255, 0, 0 ) );
RECT r;
GetClientRect( hWnd, &r );
FillRect( hdc, &r, hbrRedBrush );
DeleteObject( hbrRedBrush ); //you must delete GDI object!
EndPaint( hWnd, &ps );
}
return 0L;
In your case, I would make 4 static brushes and rework my code a little, adding the proper cleanup in WM_CLOSE handler. Below are the suggested changes:
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message,
WPARAM wParam, LPARAM lParam)
{
// add static before HBRUSH
static HBRUSH coluns=CreateSolidBrush(RGB(50,120,180));
static HBRUSH colsel=CreateSolidBrush(RGB(80,150,220));
static HBRUSH colmso=CreateSolidBrush(RGB(50,70,190));
static HBRUSH BlackBrush = CreateSolidBrush(RGB(0,0,0));
switch (message)
{
// this is the problematic handler
case WM_PAINT:
{
//the changed part
FillRect( hdc, &re, BlackBrush );
}
break;
case WM_CLOSE:
{
DeleteObject( BlackBrush );
DeleteObject( coluns );
DeleteObject( colsel );
DeleteObject( colmso );
// other clean up code
}
break;
IMPORTANT NOTE:
This time you used FillRect API, but next time you might load bitmaps and other stuff that require from you to restore HDC into original state after you are done with drawing.
You do that like this:
HBITMAP bmpOld = (HBITMAP)SelectObject( hdc, myBitmap );
// bmpOld stores the original state of the device context
// you do something with myBitmap
// then you return device context into original state
// by selecting the original value, bmpOld, back into device context
SelectObject( hdc, oldBmp );
DeleteObject( myBitmap );
Again, pay attention to WM_COMMAND handler in the above MSDN example to see how they did it.
Here is the link to a great Win32 API tutorial for beginners-give it a go.
In the end I recommend you this tool for detecting GDI leaks.
If you have further questions leave a comment and I will reply as soon as possible.
Best regards and good luck!