PowerToys/src/modules/fancyzones/FancyZonesLib/MonitorUtils.cpp

#include "pch.h"
#include "MonitorUtils.h"

#include <FancyZonesLib/util.h>

namespace MonitorUtils
{
    constexpr int CUSTOM_POSITIONING_LEFT_TOP_PADDING = 16;

    inline int RectWidth(const RECT& rect)
    {
        return rect.right - rect.left;
    }

    inline int RectHeight(const RECT& rect)
    {
        return rect.bottom - rect.top;
    }

    RECT FitOnScreen(const RECT& windowRect, const RECT& originMonitorRect, const RECT& destMonitorRect)
    {
        // New window position on active monitor. If window fits the screen, this will be final position.
        int left = destMonitorRect.left + (windowRect.left - originMonitorRect.left);
        int top = destMonitorRect.top + (windowRect.top - originMonitorRect.top);
        int W = RectWidth(windowRect);
        int H = RectHeight(windowRect);

        if ((left < destMonitorRect.left) || (left + W > destMonitorRect.right))
        {
            // Set left window border to left border of screen (add padding). Resize window width if needed.
            left = destMonitorRect.left + CUSTOM_POSITIONING_LEFT_TOP_PADDING;
            W = min(W, RectWidth(destMonitorRect) - CUSTOM_POSITIONING_LEFT_TOP_PADDING);
        }
        if ((top < destMonitorRect.top) || (top + H > destMonitorRect.bottom))
        {
            // Set top window border to top border of screen (add padding). Resize window height if needed.
            top = destMonitorRect.top + CUSTOM_POSITIONING_LEFT_TOP_PADDING;
            H = min(H, RectHeight(destMonitorRect) - CUSTOM_POSITIONING_LEFT_TOP_PADDING);
        }

        return { .left = left,
                 .top = top,
                 .right = left + W,
                 .bottom = top + H };
    }

    void OpenWindowOnActiveMonitor(HWND window, HMONITOR monitor) noexcept
    {
        // By default Windows opens new window on primary monitor.
        // Try to preserve window width and height, adjust top-left corner if needed.
        HMONITOR origin = MonitorFromWindow(window, MONITOR_DEFAULTTOPRIMARY);
        if (origin == monitor)
        {
            // Certain applications by design open in last known position, regardless of FancyZones.
            // If that position is on currently active monitor, skip custom positioning.
            return;
        }

        WINDOWPLACEMENT placement{};
        if (GetWindowPlacement(window, &placement))
        {
            MONITORINFOEX originMi;
            originMi.cbSize = sizeof(originMi);
            if (GetMonitorInfo(origin, &originMi))
            {
                MONITORINFOEX destMi;
                destMi.cbSize = sizeof(destMi);
                if (GetMonitorInfo(monitor, &destMi))
                {
                    RECT newPosition = FitOnScreen(placement.rcNormalPosition, originMi.rcWork, destMi.rcWork);
                    FancyZonesUtils::SizeWindowToRect(window, newPosition);
                }
            }
        }
    }
}