Wm_paint 100% cpu

[MasterDucky]

Hi

I'm getting 100% CPU usage because of WM_PAINT is getting called all the time.

I simplified the code to a maximum to eliminate the culprit but still getting 100% cpu usage.

#include <windows.h>
#include <time.h>
#include <string>
#include <iostream>
using namespace std;

#pragma comment(lib,"user32.lib")
#pragma comment(lib,"gdi32.lib")
#pragma comment(lib,"shell32.lib")

#pragma comment(linker, "/subsystem:\"console\" /entry:\"WinMainCRTStartup\"")


LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    HFONT    hBig, hFont;
    HDC    hdc;
    int index;

    PAINTSTRUCT     ps01;
    BITMAP          bitmap01;
    HDC             hdcMem01;
    HGDIOBJ         oldBitmap01;

    switch(message)
    {
      // Draw background image
    case WM_PAINT:

        cout << "wmpaint: " << endl;
        return 0;

    case WM_DESTROY:
        PostQuitMessage (0);
        return 0;

    } // message switch
    return DefWindowProc(hWnd, message, wParam, lParam);
}

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR lpszArgument, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT ("SineWave") ;
    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 (WHITE_BRUSH) ;
    wndclass.lpszMenuName  = NULL ;
    wndclass.lpszClassName = szAppName ;

    if (!RegisterClass (&wndclass))
    {
        MessageBox (NULL, TEXT ("Program requires Windows NT!"),
                    szAppName, MB_ICONERROR) ;
        return 0 ;
    }

    hwnd = CreateWindow (szAppName, TEXT ("Sine Wave Using Polyline"),
                         WS_OVERLAPPEDWINDOW,
                         CW_USEDEFAULT, CW_USEDEFAULT,
                         CW_USEDEFAULT, CW_USEDEFAULT,
                         NULL, NULL, hInstance, NULL) ;

    ShowWindow (hwnd, iCmdShow) ;
    UpdateWindow (hwnd) ;

    while (GetMessage (&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return msg.wParam;
}

[2kaud]

You aren't handling the WM_PAINT message properly. The minimum needed is:

PAINTSTRUCT ps; 
HDC hdc;
...
case WM_PAINT:
    hdc = BeginPaint(hwnd, &ps); 
    //TextOut(hdc, 0, 0, "wmpaint", 7); 
    EndPaint(hwnd, &ps); 
    return 0L;

It's also not a good idea to try to output to the console during a WM_PAINT message as WM_PAINT messages can occur frequently. Why are you changing the linker options?? If you want a console from within a windows program, then use AllocConsole() see https://docs.microsoft.com/en-us/win...n-of-a-console

[MasterDucky]

Thank you very much for your response 2kaud, it solved the problem!

Actually I was handeling the WM_PAINT message but I removed it for simplicity's sake as it was causing the same symptom.

But now I realized that the problem was that I was calling LoadImage() in WM_CREATE:.
Now if I call it in WM_PAINT, there is no more high CPU usage.

    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);
        hBitmap01 = (HBITMAP)LoadImage(NULL, szFileName, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
   
        if (hBitmap01==NULL)
            MessageBox(NULL, "Error Loading Image.", "ERROR", MB_ICONWARNING);

        hdcMem01 = CreateCompatibleDC(hdc);
        oldBitmap01 = SelectObject(hdcMem01, hBitmap01);

        GetObject(hBitmap01, sizeof(bitmap01), &bitmap01);
        BitBlt(hdc, 0, 0, bitmap01.bmWidth, bitmap01.bmHeight, hdcMem01, 0, 0, SRCCOPY);

        SelectObject(hdcMem01, oldBitmap01);
        DeleteDC(hdcMem01);

        EndPaint(hWnd, &ps);
       
        return 0;

Im changing the linker options just in order to debug the program. Because I dont want to create a whole project in Visual Studio just for the sake of testing a small program.

Anyway you made my day, Im really grateful.

[MasterDucky]

I tried to use AllocConsole() but cout or printf wont print anything to the console.

[2kaud]

I tried to use AllocConsole() but cout or printf wont print anything to the console.

You need to re-direct stdout to the console. See
https://stackoverflow.com/questions/...isplaying-cout
https://www.codeproject.com/articles...-from-a-gui-ap

Try:

AllocConsole();
static ofstream conout("CONOUT$", ios::out); 
cout.rdbuf(conout.rdbuf());
...
cout << "Hello World" << endl;

or

AllocConsole();
FILE* fp;
freopen_s(&fp, "CONOUT$", "w", stdout);
std::cout.clear();
...
cout << "Hello World"  << endl;

[MasterDucky]

Great, thanks!