C++ GDI+ Objects Memory leak/too many objects? - c++

Question

ive been making a c++ drawing program and i have a part where im drawing using gdi+ inside a function so i need to declare my graphics object every time i call the function.. this obviously is wrong and causes a leak somewhere so after some calls it gets slower and then suddenly stops drawing all together ,as expected.
im trying to clear my objects every time it finishes drawing but it doesnt seem to solve the issue. i thought maybe the PEN objects are part of the issue but some insight would be very helpful
my code:
void function()
{
DWORD pdwGduStartup;
GdiplusStartupInput GdiStartupInp;
GdiplusStartup(&pdwGduStartup, &GdiStartupInp, NULL);
Pen pnPen_Blue(Gdiplus::Color(255, 0, 0, 255), 2.0F);
Pen pnPen_Green(Gdiplus::Color(255, 255, 0, 255), 2.0F);
LPCSTR LGameWindow = "MyWindow";
HWND hGameWindow = FindWindow(NULL, LGameWindow);
Graphics graphics(GetDC(hGameWindow));
for (int n=10; n>0; n--)
graphics.DrawLine(&pnPen_Green,0, 0, 0, n);
GdiplusShutdown(pdwGduStartup);
graphics.Flush();
}
thanks alot!
edit: added release DC did not do anything!
DWORD pdwGduStartup;
GdiplusStartupInput GdiStartupInp;
GdiplusStartup(&pdwGduStartup, &GdiStartupInp, NULL);
Pen pnPen_Blue(Gdiplus::Color(255, 0, 0, 255), 2.0F);
Pen pnPen_Green(Gdiplus::Color(255, 255, 0, 255), 2.0F);
LPCSTR LGameWindow = "MyWindow";
HWND hGameWindow = FindWindow(NULL, LGameWindow);
HDC GDC = GetDC(hGameWindow);
Graphics graphics(GDC);
ReleaseDC(hGameWindow, GDC);
GdiplusShutdown(pdwGduStartup);
graphics.Flush();
My GDI objects still rises up to 10,000!

Answer 1

GdiplusShutdown must be called after all GDI+ objects are removed. In your code Pen and Graphics destructors are called after GdiplusShutdown, when the objects go out of scope.

Answer 2

I guess the problem is in GetDC. You should call ReleaseDC or use WTL smart pointers.
As I remember such things where easy to debug with task manager. It shows HANDLE count as well as GDI object count for a process, so you can see what lines generate new objects.

Answer 3

I didnt code my GDI+ right logically. in the logic first you need to create the graphics object, and only then loop draw on it. anything else is WRONG and code wont fix it!

Answer 4

Try something like this, use pointers that you can easily delete when done.
DWORD pdwGduStartup;
GdiplusStartupInput GdiStartupInp;
GdiplusStartup(&pdwGduStartup, &GdiStartupInp, NULL);
Pen pnPen_Blue* = new Pen(Gdiplus::Color(255, 0, 0, 255), 2.0F);
Pen pnPen_Green* = new Pen(Gdiplus::Color(255, 255, 0, 255), 2.0F);
LPCSTR LGameWindow = "MyWindow";
HWND hGameWindow = FindWindow(NULL, LGameWindow);
HDC GDC = GetDC(hGameWindow);
Graphics* g = new Graphics(GDC);
// Do stuff here
ReleaseDC(hGameWindow, GDC);
delete pnPen_Blue;
delete pnPen_Green;
g->Flush();
delete g;
delete GDC; // not sure
GdiplusShutdown(pdwGduStartup);