C++ Display Enumeration Sample (Windows only) Complete Code

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#include <interaction_lib/InteractionLib.h>
#include <interaction_lib/misc/InteractionLibPtr.h>
#include <windows.h>
#include <vector>
#include <functional>
#include <DisplayEnumerationHelper.h>
// This a simple C++ wrapper for a Win32 HWND window representation.
// Note that there is no real error handling, since its main purpose
// is to support the Interaction Library SDK C++ sample that shows how
// to use the display enumeration helper functions.
class Window final
// Window creation might trigger all of the OnPaint, OnMove and OnSize events.
void Create();
// When a window is repainted, the OnPaint event is triggered.
void Repaint();
// The int& out parameter tells the window what Win32 system color index it should
// use when painting its client area, for instance COLOR_WINDOW or COLOR_HIGHLIGHT.
std::function<void(int&)> OnPaint;
// The float parameters are the new x and y positions of the window client area
// origo, relative to the primary screen origo.
std::function<void(float, float)> OnMove;
// The float parameters are the new width and height of the window client area.
std::function<void(float, float)> OnSize;
// The window procedure handles messages that are needed to invoke the public events.
static LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp);
HWND m_hwnd{};
void Window::Create()
wc.hInstance = GetModuleHandle(nullptr);
wc.lpfnWndProc = WindowProcedure;
wc.lpszClassName = "TobiiInteractorWindow";
CreateWindowA(wc.lpszClassName, "Interactor Window",
NULL, NULL, GetModuleHandle(nullptr), this);
void Window::Repaint()
InvalidateRect(m_hwnd, NULL, FALSE);
LRESULT Window::WindowProcedure(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
static Window* window{};
switch (msg)
CREATESTRUCTA* cs{reinterpret_cast<CREATESTRUCTA*>(lp)};
window = static_cast<Window*>(cs->lpCreateParams);
window->m_hwnd = hwnd;
return 0;
case WM_MOVE:
if (window->OnMove)
POINT offset{};
ClientToScreen(hwnd, &offset);
const float x = static_cast<float>(offset.x);
const float y = static_cast<float>(offset.y);
window->OnMove(x, y);
return 0;
case WM_SIZE:
if (window->OnSize)
RECT rect{};
GetClientRect(hwnd, &rect);
const float width = static_cast<float>(rect.right - rect.left);
const float height = static_cast<float>(rect.bottom - rect.top);
window->OnSize(width, height);
return 0;
return 1;
case WM_PAINT:
HDC hdc{BeginPaint(hwnd, &ps)};
int sysColorIndex = COLOR_WINDOW;
if (window->OnPaint)
FillRect(hdc, &ps.rcPaint, GetSysColorBrush(sysColorIndex));
EndPaint(hwnd, &ps);
return 0;
window->m_hwnd = nullptr;
window = nullptr;
return 0;
return DefWindowProc(hwnd, msg, wp, lp);
// This one way to implement a Win32 "message pump" that not only
// handles window input from the user and the system, but also
// integrates with an external "event source" - an eye tracker.
bool ProcessMessages()
MSG msg{};
while (PeekMessageA(&msg, NULL, 0, 0, PM_REMOVE))
// When the window is destroyed, it posts a quit message,
// which is picked up here as "stop processing messages".
if (msg.message == WM_QUIT)
return false;
return true;
// create the interaction library
IL::UniqueInteractionLibPtr intlib{IL::CreateInteractionLib(IL::FieldOfUse::Interactive)};
// This is just a helper function to make the underlying C function
// easier to use in a C++ context.
auto GetMonitorDisplayAreas = []
std::vector<MonitorDisplayAreaA> areas{5}; // unusual to have more than 5 monitors...
int found{};
// This is the raw C display area enumeration helper function.
// It will enumerate all displays on the windows machine, including their virtual
// screen bounds and display IDs, and put the results into the supplied array of structs.
// The display IDs have the same formatting as are used on Tobii eyetrackers to
// identify which display they are attached to.
EnumerateDisplayAreasA(areas.data(), &found, static_cast<int>(areas.size()));
return areas;
// When all displays are identified, pass their information to the Interaction Library.
for (const auto& area : GetMonitorDisplayAreas())
// For each display we tell the Interaction Library
// 1) the coordinate scaling we want to use by giving the size as we see it
// 2) the size and origin in virtual screen coordinates, and
// 3) the ID of the display.
// Interaction Library will use this information to map connected devices to display areas,
// to transform all data streams when outputting them and to properly transform all added
// interactors to its internal, global coordinate space when performing gaze focus calculations.
// Here we are using the native scaling (so first to parameters are the same as the virtual
// screen size) but we could have used any scaling we like, eg (1.0, 1.0) for relative
// coordinates.
area.wVirtual, area.hVirtual,
area.wVirtual, area.hVirtual,
area.xVirtual, area.yVirtual,
// All events must have handlers before the physical window is created, so that
// any resizing, moving and painting done by the system during window creation
// is picked up by our application logic.
Window window;
// By telling the Interaction Library to offset the coordinate system origin
// so that it matches the location of the window client area, we can add and
// update interactors using window-local coordinates.
// The origin offset has to be in the virtual coordinate space we used when
// adding the display areas above.
window.OnMove = [&] (float x, float y)
intlib->CoordinateTransformSetOriginOffset(x, y);
// In this sample we want the entire window client area to be an interactor
// that changes color when it gets and loses gaze focus.
window.OnSize = [&] (float width, float height)
// setup the window client area as an interactor
intlib->AddOrUpdateInteractor(0, {0.0f, 0.0f, width, height}, 0.0f);
struct GazeFocusEventContext final
bool focused;
Window& window;
} gazeFocusEventContext{false, window};
// Subscribe to gaze focus events. When the window client area (which is an
// interactor) gets or loses gaze focus, the "focused" flag is set and then
// the window is repainted.
intlib->SubscribeGazeFocusEvents([](IL::GazeFocusEvent evt, void* context)
auto gazeFocusEventContext{static_cast<GazeFocusEventContext*>(context)};
gazeFocusEventContext->focused = evt.hasFocus;
}, &gazeFocusEventContext);
// When the window repaints itself, it invokes this event to ask for the color to use.
window.OnPaint = [&] (int& sysColorIndex)
sysColorIndex = gazeFocusEventContext.focused ? COLOR_HIGHLIGHT : COLOR_WINDOW;
// Now that all events and subscriptions are set up, the physical window can be created.
// Handle window events and update interaction library to trigger all callbacks
while (ProcessMessages())
return 0;