Find image on screen - c++

Question

I wonder how to solve this problem. I want to check every X seconds if the screen contains an image (for example a red dot) and if so return True. I am very familiar with Python, and there are some easy solutions there. But I haven't found a similar solution yet.
What I basically want to do is:
Take a screenshot
Locate image X on the screenshot
Return bool
Looked into OpenCV and would be possible to solve it that way, but might be a bit overextending. I was thinking about getPixel to loop over all the pixels in the screen. But it's extremely slow.
#include <Windows.h>
#include <iostream>
using namespace std;
int main()
{
HWND runelite = GetForegroundWindow();
HMONITOR monitor = MonitorFromWindow(runelite, MONITOR_DEFAULTTONEAREST);
MONITORINFO info;
info.cbSize = sizeof(MONITORINFO);
GetMonitorInfo(monitor, &info);
int monitor_width = info.rcMonitor.right - info.rcMonitor.left;
int monitor_height = info.rcMonitor.bottom - info.rcMonitor.top;
int r, g, b;
HDC screenshot = GetDC(NULL);
for (int i = 0; i < monitor_height; i++) {
for (int j = 0; j < monitor_width; j++) {
DWORD color = GetPixel(screenshot, j, i);
cout << "Scanning -> X: " << j << " Y: " << i << endl;
r = GetRValue(color);
g = GetGValue(color);
b = GetBValue(color);
if (r == 0 && g == 0 && b == 0) {
cout << "Button found by color!" << endl;
goto end;
}
}
}
end:
ReleaseDC(NULL, screenshot);
return 0;
}

Answer 1

you could greatly increase the speed if you copy your HDCs content to another bitmap and get a pointer to the image data and loop over this.
create a memory bitmap
HDC memDC = CreateCompatibleDC ( hDC );
HBITMAP memBM = CreateCompatibleBitmap ( hDC, nWidth, nHeight );
SelectObject ( memDC, memBM );
then bitblt the screen data to that bitmap via BitBlt and get the bitmap data with GetDIBits.
please also note, that GetDC(NULL) does not make a screenshot, but gets you access to windows live main HDC. drawing to it directly draws on the desktop.
Thatswhy every GetPixel on it does take quite long.