Match the monitor index to the enumeration order of `EnumDisplayMonitors()`

[yeongjet]

I wanna capture screen output by indices from virtual-display-cli after adding monitor, but the index in virtual display cli is not match the order of EnumDisplayMonitors().
Without this feature I have to use EnumDisplayMonitors() to enum all display monitors to choose indices, any other resolvetion?

#include "screen.h"
#include <windows.h>
#include <d3d11.h>
#include <dxgi1_2.h>
#include <wrl/client.h>

using Microsoft::WRL::ComPtr;
// capture screen output by index
int capture(
    ComPtr<ID3D11Texture2D> &outTexture,
    D3D11_TEXTURE2D_DESC *outDesc,
    UINT screenIndex) // I want it from virtual-display-cli output
{
    ComPtr<ID3D11Device> device = nullptr;
    ComPtr<ID3D11DeviceContext> context = nullptr;
    D3D_FEATURE_LEVEL featureLevel;
    HRESULT hr = D3D11CreateDevice(
        nullptr, D3D_DRIVER_TYPE_HARDWARE, nullptr, 0, nullptr, 0,
        D3D11_SDK_VERSION, &device, &featureLevel, &context);
    if (FAILED(hr))
    {
        return -1;
    }
    ComPtr<IDXGIDevice> dxgiDevice;
    device.As(&dxgiDevice);
    ComPtr<IDXGIAdapter> dxgiAdapter;
    dxgiDevice->GetAdapter(&dxgiAdapter);
    ComPtr<IDXGIOutput> dxgiOutput;
  // the first param is match the order of  EnumDisplayMonitors(), which means screenIndex from cli can't be passed
    hr = dxgiAdapter->EnumOutputs(screenIndex, &dxgiOutput);
    if (FAILED(hr))
    {
        return -10; 
    }
    ComPtr<IDXGIOutput1> dxgiOutput1;
    dxgiOutput.As(&dxgiOutput1);
    ComPtr<IDXGIOutputDuplication> deskDupl;
    hr = dxgiOutput1->DuplicateOutput(device.Get(), &deskDupl);
    if (FAILED(hr))
    {
        return -2;
    }
    DXGI_OUTDUPL_FRAME_INFO frameInfo;
    ComPtr<IDXGIResource> desktopResource;
    hr = deskDupl->AcquireNextFrame(1000, &frameInfo, &desktopResource);
    if (FAILED(hr))
    {
        return -3;
    }
    ComPtr<ID3D11Texture2D> acquiredDesktopImage;
    desktopResource.As(&acquiredDesktopImage);
    D3D11_TEXTURE2D_DESC desc = {};
    acquiredDesktopImage->GetDesc(&desc);
    if (outDesc)
        *outDesc = desc;
    D3D11_TEXTURE2D_DESC descStaging = desc;
    descStaging.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
    descStaging.Usage = D3D11_USAGE_STAGING;
    descStaging.BindFlags = 0;
    descStaging.MiscFlags = 0;
    ComPtr<ID3D11Texture2D> stagingTex;
    hr = device->CreateTexture2D(&descStaging, nullptr, &stagingTex);
    if (FAILED(hr))
    {
        deskDupl->ReleaseFrame();
        return -4;
    }
    context->CopyResource(stagingTex.Get(), acquiredDesktopImage.Get());
    deskDupl->ReleaseFrame();
    outTexture = stagingTex;
    return 0;
}

//get screens(with resolutions info) by indices from cli
std::vector<Screen> getScreens(const std::vector<int> &indices)
{
    std::vector<Screen> screens;
    int monitorCount = 0;
    std::vector<std::pair<uint16_t, uint16_t>> resolutions;
// the order is not match the indices from cli
    EnumDisplayMonitors(
        nullptr, nullptr,
        [](HMONITOR hMon, HDC hdcMon, LPRECT lprcMon, LPARAM pData) -> BOOL
        {
            auto res = reinterpret_cast<std::vector<std::pair<uint16_t, uint16_t>> *>(pData);
            MONITORINFOEX mi;
            mi.cbSize = sizeof(mi);
            if (GetMonitorInfo(hMon, &mi))
            {
       // output:  "Monitor name:  \\.\DISPLAY1", there is no monitor name in cli output, I can't use it to find the target monitor
                printf("Monitor name: %s\n", mi.szDevice); 
                DEVMODE dm;
                dm.dmSize = sizeof(dm);
                if (EnumDisplaySettings(mi.szDevice, ENUM_CURRENT_SETTINGS, &dm))
                {
                    res->emplace_back(static_cast<uint16_t>(dm.dmPelsWidth), static_cast<uint16_t>(dm.dmPelsHeight));
                }
            }
            return TRUE;
        },
        reinterpret_cast<LPARAM>(&resolutions));

    for (int idx : indices)
    {
        if (idx >= 0 && idx < static_cast<int>(resolutions.size()))
        {
            screens.push_back({idx,
                               resolutions[idx].first,
                               resolutions[idx].second});
        }
    }
    return screens;
}

[MolotovCherry]

The monitor indices purpose is specifically for the user. It is not meant to be any specific index; the user is allowed to manually set it so they can customize the list order to their liking or assign a special number (index) to specific monitors. As a result, it should not be relied upon for using in any system api.

Unfortunately, I don't know of a better way to solve your issue at this moment, but I suspect the solution you are using right now is probably the right solution, or at least, you're on the right path. Right now, to know which monitors are virtual monitors, I would probably suggest to check the adapter or description of a monitor. The adapter/string is not likely to ever change, so it should be a fairly stable way of determining which monitors are virtual.

I don't plan on exposing any internal system details in my api at the moment, as any developer could just use windows apis to do what they need anyways. But if I do eventually need to expose some of these details in my api, the proper way to do this would be to connect to the pipe created by the driver, and use the drivers protocol to ask for any specific information you want.

I am currently waiting on windows-drivers-rs to mature before I continue development, as I'd like to port the driver over. They're still missing a lot of crucial C++ macros I need. Until then, it's not likely I will be continuing development on the current driver's code.

[yeongjet]

Got it, thank you. @MolotovCherry

[MolotovCherry]

I don't think this request is out of scope. I'll keep it open for when I do the port

[yeongjet]

I really appreciate.