Winapi c++ trying to get primary monitor's brightness - c++

Question

I tried to get the brightness of the primary monitor using the following code:
POINT monitorPoint = { 0, 0 };
HANDLE monitor = MonitorFromPoint(monitorPoint, MONITOR_DEFAULTTOPRIMARY);
DWORD minb, maxb, currb;
if (GetMonitorBrightness(monitor, &minb, &currb, &maxb) == FALSE) {
std::cout << GetLastError() << std::endl;
}
But it fails and GetLastError() returns 87 which means Invalid Parameter.
EDIT: I managed to solve this using EnumDisplayMonitors() and GetPhysicalMonitorsFromHMONITOR() like this:
std::vector<HANDLE> pMonitors;
BOOL CALLBACK MonitorEnumProc(HMONITOR hMonitor, HDC hdcMonitor, LPRECT lprcMonitor, LPARAM dwData) {
DWORD npm;
GetNumberOfPhysicalMonitorsFromHMONITOR(hMonitor, &npm);
PHYSICAL_MONITOR *pPhysicalMonitorArray = new PHYSICAL_MONITOR[npm];
GetPhysicalMonitorsFromHMONITOR(hMonitor, npm, pPhysicalMonitorArray);
for (unsigned int j = 0; j < npm; ++j) {
pMonitors.push_back(pPhysicalMonitorArray[j].hPhysicalMonitor);
}
delete pPhysicalMonitorArray;
return TRUE;
}
// and later inside main simply:
EnumDisplayMonitors(NULL, NULL, MonitorEnumProc, NULL);
// and when I need to change the brightness:
for (unsigned int i = 0; i < pMonitors.size(); ++i) {
SetMonitorBrightness(pMonitors.at(i), newValue);
}
Now I encounter 2 new problems:
1) From EnumDisplayMonitors() I get 2 monitor handles since I have 2 monitors. The problem is that only my primary works. Whenever I try to so something with the secondary monitor I get this error:
0xC0262582: ERROR_GRAPHICS_I2C_ERROR_TRANSMITTING_DATA
2) After using SetMonitorBrightness() for some time it stops working even for the primary monitor and I get the following error:
0xC026258D

Answer 1

You are passing an HMONITOR to the function. However, its documentation states that a handle to a physical monitor is required instead, and suggests that you call GetPhysicalMonitorsFromHMONITOR() to obtain it. Indeed, since MonitorFromPoint() returns an HMONITOR your code would have failed to compile with STRICT enabled, a practise that helps root out such mistakes.
You should include error checking for the call to MonitorFromPoint(). And the documentation also suggests that you should call GetMonitorCapabilities() passing MC_CAPS_BRIGHTNESS to make sure the monitor supports brightness requests.
Please refer to the documentation of GetMonitorBrightness() for more detail: