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how to release HDC object

Jan 8, 2023 at 9:10am
jNc (66)
HDC object hwindowDC increase memory,but it must be flushed with destructor
tried below
DeleteObject(hwindowDC);
DeleteDC(hwindowDC);
CancelDC(hwindowDC);


Function hwindowDC = GetDC(hwnd) can not be flushed with destructor functions I use

I need to flush all memory related to functions below.
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class hwnd2Mat
{
public:
    hwnd2Mat(HWND hwindow, float scale = 1);
    virtual ~hwnd2Mat();
    virtual void read();
    Mat image;

private:
    HWND hwnd;
    HDC hwindowDC, hwindowCompatibleDC;
    int height, width, srcheight, srcwidth;
    HBITMAP hbwindow;
    BITMAPINFOHEADER  bi;
};

hwnd2Mat::hwnd2Mat(HWND hwindow, float scale)
{
    hwnd = hwindow;
    hwindowDC = GetDC(hwnd);  
    hwindowCompatibleDC = CreateCompatibleDC(hwindowDC);
   SetStretchBltMode(hwindowCompatibleDC, COLORONCOLOR);
    RECT windowsize;
    GetClientRect(hwnd, &windowsize);
   srcheight = windowsize.bottom;
    srcwidth = windowsize.right;
    height = (int)(windowsize.bottom * scale);
    width = (int)(windowsize.right * scale);
    image.create(height, width, CV_8UC4);
    hbwindow = CreateCompatibleBitmap(hwindowDC, width, height);
    bi.biSize = sizeof(BITMAPINFOHEADER);
    bi.biWidth = width;
    bi.biHeight = -height;
    bi.biPlanes = 1;
    bi.biBitCount = 32;
    bi.biCompression = BI_RGB;
    bi.biSizeImage = 0;
    bi.biXPelsPerMeter = 0;
    bi.biYPelsPerMeter = 0;
    bi.biClrUsed = 0;
    bi.biClrImportant = 0;
    SelectObject(hwindowCompatibleDC, hbwindow);
    read();

};

void hwnd2Mat::read()
{
    StretchBlt(hwindowCompatibleDC, 0, 0, width, height, hwindowDC, 0, 0, srcwidth, srcheight, SRCCOPY); //change SRCCOPY to NOTSRCCOPY for wacky colors !
    GetDIBits(hwindowCompatibleDC, hbwindow, 0, height, image.data, (BITMAPINFO*)&bi, DIB_RGB_COLORS);  //copy from hwindowCompatibleDC to hbwindow
};

hwnd2Mat::~hwnd2Mat()
{
    DeleteObject(hbwindow);
    DeleteDC(hwindowCompatibleDC);
    ReleaseDC(hwnd, hwindowDC);
    DeleteObject(hwindowDC);
    DeleteDC(hwindowDC);
    CancelDC(hwindowDC);


    //hwindowDC = GetDC(hwnd);
    image.release(); 

}



void screenCapture ()
{

    hwnd2Mat capDesktop(GetDesktopWindow());
    VideoWriter writer;  
    int codec = VideoWriter::fourcc('X', 'V', 'I', 'D');
    double fps = 10.0;
    string filename = "./caP3.mkv";
    writer.open(filename, codec, fps, capDesktop.image.size(), true);
    capDesktop.read();
    cvtColor(capDesktop.image, image1, COLOR_BGRA2BGR);  
}

can not add code tag
Last edited on Jan 8, 2023 at 9:11am
Jan 8, 2023 at 10:58am
seeplus (6616)
The reverse of GetDC() is ReleaseDC()
https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-releasedc

The reverse of CreateCompatibleDC() is DeleteDC()
https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-deletedc

The reverse of CreateCompatibleBitmap() is DeleteObject()
https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-deleteobject

As are already used.
Last edited on Jan 8, 2023 at 12:06pm
Jan 8, 2023 at 11:07am
jNc (66)
The ReleaseDC function releases a device context (DC), freeing it for use by other applications. The effect of the ReleaseDC function depends on the type of DC. It frees only common and window DCs. It has no effect on class or private DCs.
is there any other way to solve this?
Jan 8, 2023 at 11:09am
jNc (66)
I already tried these, but It have no effect

ReleaseDC(hwnd, hwindowDC);
DeleteObject(hwindowDC);
DeleteDC(hwindowDC);
CancelDC(hwindowDC);

need to flush all related to hwindowDC
Jan 8, 2023 at 11:34am
seeplus (6616)
Re GetDC()

From MSDN
After painting with a common DC, the ReleaseDC function must be called to release the DC. Class and private DCs do not have to be released. ReleaseDC must be called from the same thread that called GetDC. The number of DCs is limited only by available memory.


https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getdc

Jan 8, 2023 at 12:05pm
jNc (66)
still does not flush memory
Jan 8, 2023 at 12:37pm
seeplus (6616)
How do you know?
Jan 8, 2023 at 12:42pm
jNc (66)
I check with application

int processNumber = _getpid();


int PrintMemoryInfo( DWORD processID ){
HANDLE hProcess;
PROCESS_MEMORY_COUNTERS pmc;
if (processID == processNumber)
hProcess = OpenProcess( PROCESS_QUERY_INFORMATION | PROCESS_VM_READ,FALSE, processID );
//if (NULL == hProcess)
//return 1;
else
return 0;
if (processID == processNumber)
if ( GetProcessMemoryInfo( hProcess, &pmc, sizeof(pmc)))
temp = pmc.WorkingSetSize;
hProcess = NULL;
//CloseHandle( hProcess );
return temp;
}

wait I will share you code
[shared a code]

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#define WINVER 0x0500
#include <tesseract/baseapi.h>
#include <leptonica/allheaders.h>
#include <opencv2/opencv.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/videoio.hpp>
#include <iostream>
#include <fstream>
#include <Windows.h>
#include <iostream>
#include <string>
#include <iomanip>
#include <QFile>
#include <cstdlib>
#include <windows.h>
#include <stdio.h>
#include <psapi.h>
#include <iostream>
#include <iomanip>
using std::cout;
using std::endl;
using std::cin;
using std::ios;
using std::setiosflags;
using std::hex;
using std::oct;
using std::dec;
using std::cout;
using std::endl;
using std::cin;
using std::ios;
using std::setiosflags;
using std::hex;
using std::oct;
using std::dec;
using namespace std;

void screenCapture ();
int PrintMemoryInfo( DWORD processID );

class hwnd2Mat
{
public:
    hwnd2Mat(HWND hwindow, float scale = 1);
    virtual ~hwnd2Mat();
    virtual void read();
    cv::Mat image;

private:
    HWND hwnd;
    HDC hwindowDC, hwindowCompatibleDC;
    int height, width, srcheight, srcwidth;
    HBITMAP hbwindow;
    BITMAPINFOHEADER  bi;
};

hwnd2Mat::hwnd2Mat(HWND hwindow, float scale)
{

    hwnd = hwindow;
    hwindowDC = GetDC(hwnd);
    hwindowCompatibleDC = CreateCompatibleDC(hwindowDC);
    SetStretchBltMode(hwindowCompatibleDC, COLORONCOLOR);
    RECT windowsize;
    GetClientRect(hwnd, &windowsize);
    srcheight = windowsize.bottom;
    srcwidth = windowsize.right;
    height = (int)(windowsize.bottom * scale);
    width = (int)(windowsize.right * scale);
    image.create(height, width, CV_8UC4);
    ReleaseDC(hwnd, hwindowDC);
    hbwindow = CreateCompatibleBitmap(hwindowDC, width, height);
    bi.biSize = sizeof(BITMAPINFOHEADER);
    bi.biWidth = width;
    bi.biHeight = -height;
    bi.biPlanes = 1;
    bi.biBitCount = 32;
    bi.biCompression = BI_RGB;
    bi.biSizeImage = 0;
    bi.biXPelsPerMeter = 0;
    bi.biYPelsPerMeter = 0;
    bi.biClrUsed = 0;
    bi.biClrImportant = 0;
    SelectObject(hwindowCompatibleDC, hbwindow);
    read();



}

void hwnd2Mat::read(){
    StretchBlt(hwindowCompatibleDC, 0, 0, width, height, hwindowDC, 0, 0, srcwidth, srcheight, SRCCOPY); //change SRCCOPY to NOTSRCCOPY for wacky colors !
    GetDIBits(hwindowCompatibleDC, hbwindow, 0, height, image.data, (BITMAPINFO*)&bi, DIB_RGB_COLORS);  //copy from hwindowCompatibleDC to hbwindow
    }

hwnd2Mat::~hwnd2Mat(){
    DeleteObject(hbwindow);
    DeleteDC(hwindowCompatibleDC);
    ReleaseDC(hwnd, hwindowDC);
    image.release();
    cout << "destructor called" << endl;
    }

int main()
{
    int processNumber = _getpid();
    int i = 0;
    int memoryLoad = 0;
    int first = 0;
    while (true)
    {
    cout << i << endl;
    screenCapture();
    memoryLoad = PrintMemoryInfo( processNumber );
    cout << " Load " << memoryLoad << " MB " <<  memoryLoad/1000000  <<  endl;
    if (i == 0 )
    first = memoryLoad;

    cout << "first " << first << endl;
    cout << "load "  << memoryLoad << endl;
    i++;
    }

}


int PrintMemoryInfo( DWORD processID ){
    int memory_value;
    int processNumber = _getpid();
    HANDLE hProcess;
    PROCESS_MEMORY_COUNTERS pmc;
    if (processID == processNumber)
    hProcess = OpenProcess(  PROCESS_QUERY_INFORMATION | PROCESS_VM_READ,FALSE, processID );
    else
    return 0;
    if (processID == processNumber)
    if ( GetProcessMemoryInfo( hProcess, &pmc, sizeof(pmc)))
    memory_value = pmc.WorkingSetSize;
    hProcess = NULL;
    return memory_value;
               }




    void screenCapture (){
    cv::Mat capturedImage;
    hwnd2Mat capDesktop(GetDesktopWindow());
    cv::VideoWriter writer;
    int codec = cv::VideoWriter::fourcc('X', 'V', 'I', 'D');
    double fps = 10.0;
    string filename = "./caP3.mkv";
    writer.open(filename, codec, fps, capDesktop.image.size(), true);
    capDesktop.read();
    cv::cvtColor(capDesktop.image, capturedImage, cv::COLOR_BGRA2BGR);
    }
Edit & Run

Last edited on Jan 8, 2023 at 1:31pm
Jan 10, 2023 at 4:25pm
deleted account xyzzy (5768)
still does not flush memory

It's Windows, using the Window API. Windows manages memory and constructs by its own schemes.

Get used to it.

Jan 11, 2023 at 8:12am
coder777 (8447)
still does not flush memory
On line 72 the window dc is released. I.e. you don't have access to the hwindowDC anymore. I suggest to move line 72 after line 86. Or due to line 100 remove line 72 entirely
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