C++ call functions internally

Question

I'm working with following code which gives access to low level monitor configuration using Windows APIs https://github.com/scottaxcell/winddcutil/blob/main/winddcutil/winddcutil.cpp

And I would like to create a new function that increases or decreases the brightness, I was able to do this using Powershell but since the C++ code looks somewhat easy to understand I want to have a crack at it and try my luck and hopefully integrate it with an ambient light sensor later.

The powershell code I have is as follows which works with above executable: (its very crude at this stage)

$cb = [int]([uint32]("0x" + ((C:\Users\Nick\WindowsScripts\winddcutil-main\x64\Release\winddcutil.exe getvcp 0 10) -join "`n").split(" ")[2]))

if ($args[0] -eq "increase") {
    if ( $cb -ne 100) {
        $nb = "{0:x}" -f ($cb + 10)
        C:\Users\Nick\WindowsScripts\winddcutil-main\x64\Release\winddcutil.exe setvcp 0 10 $nb
    }
} elseif ($args[0] -eq "decrease") {
    if ( $cb -ne 10) {
        $nb = "{0:x}" -f ($cb - 10)
        C:\Users\Nick\WindowsScripts\winddcutil-main\x64\Release\winddcutil.exe setvcp 0 10 $nb
    }
}

It gets current brightness and if argument given is "increase" and if brightness is not already 100 then adds 10, in case of "decrease" it subtracts 10. Values are coveted to and from hex to decimals.

I understand if I want to integrate this inside the C++ code directly I would have something like following:

int increaseBrightness(std::vector<std::string> args) {
    size_t did = INT_MAX;
    did = std::stoi(args[0]);

    //0 is monitor ID and 10 is the feature code for brightness
    //currentBrightness = getVcp("0 10")
    //calculate new value
    //setVcp("0 10 NewValue")
    
}

Ultimetaly I would like to call the executable like "winddcutil.exe increasebrightness 0" (0 being the display ID)

I can keep digging around on how to do the calculation in C++ but internally calling the functions and passing the arguments so far turned out to be very challenging for me and I would appreciate some help there.

Answer 1

you need to add a needed option here line 164

std::unordered_map<std::string,std::function<int(std::vector<std::string>)>> commands
    {
        { "help", printUsage },
        { "detect", detect},
        { "capabilities", capabilities },
        { "getvcp", getVcp },
        { "setvcp", setVcp},
        {"increasebrightness ", increaseBrightness } // update here
    };

to get current brightness you can't use getVcp api due to its result will be printed to stdout , it isn't returned via returned value, follow getVcp to get brighness value , use this

DWORD currentValue;
bool success = GetVCPFeatureAndVCPFeatureReply(physicalMonitorHandle, vcpCode, NULL, &currentValue, NULL);
if (!success) {
    std::cerr << "Failed to get the vcp code value" << std::endl;
    return success;
}

then define your increaseBrightness like

int increaseBrightness(std::vector<std::string> args) {
    size_t did = INT_MAX;
    did = std::stoi(args[0]);
    
    DWORD currentBrightness;

    bool success = GetVCPFeatureAndVCPFeatureReply(
        physicalMonitorHandle, vcpCode, NULL, &currentBrightness, NULL);
    if (!success) {
        std::cerr << "Failed to get the vcp code value" << std::endl;
        return success;
    }
    //example + 10
    auto newValue = did + 10;
    success = setVcp({"0", "10", std::to_string(newValue)});
    if(success)
    {
        // your handler
    }
    // 0 is monitor ID and 10 is the feature code for brightness
    // currentBrightness = getVcp("0 10")
    // calculate new value
    // setVcp("0 10 NewValue")
}

test for passing argument: https://godbolt.org/z/5n5Gq3d7e

note: make sure your have increaseBrightness's declaration before std::unordered_map<std::string,std::function<int(std::vector<std::string>)>> commands to avoid compiler's complaint