Fix event capture in multi-window applications on macOS

[BingoXuan]

Description:
When using Dear ImGui in a macOS application with multiple windows, input events from windows without ImGui views are incorrectly captured by the global event monitor in the OSX backend.

Reproduction steps:

1. Create a macOS application with two windows
2. Add ImGui view to Window A only
3. Try to interact with Window B
4. Observe that mouse events in Window B are being captured by ImGui

Fix:
Added window check in ImGui_ImplOSX_HandleEvent to ensure events are only processed when they originate from the window containing the ImGui view:

static bool ImGui_ImplOSX_HandleEvent(NSEvent* event, NSView* view)
{
    // Only process events from the window containing ImGui view
    if (event.window != view.window) {
        return false;
    }
    // ... rest of the event handling logic
}

Testing:

1. Build test application with:
   • Window A containing ImGui view
   • Window B without ImGui
2. Verify Window B receives events normally
3. Verify ImGui functionality in Window A works correctly

[ocornut]

Hello,
Could you confirm the equivalent patch for multi-viewport mode (docking branch) ?

I believe it should be something like:

if (ImGui::FindViewportByPlatformHandle(view.window) == nulltr)
    return;

It would be good to test it.

[BingoXuan]

Following code has been verified in docking branch. And sync code to this pr.

static bool ImGui_ImplOSX_HandleEvent(NSEvent* event, NSView* view)
{

    // get window of event and view
    void *event_handle = (__bridge void*)(event.window);
    void *view_handle = (__bridge void*)(view.window);
    // check if the event and view are valid
    if (event_handle == nullptr || view_handle == nullptr)
    {
        return false;
    }
    // find viewport by platform handle, if not found return false
    ImGuiViewport *viewport = ImGui::FindViewportByPlatformHandle(view_handle);
    if(viewport == nullptr)
    {
        return false;
    }
    // check if the event and view are the same, handle event from same window

    if(viewport->PlatformHandleRaw != event_handle)
    {
        return false;
    }

    ImGuiIO& io = ImGui::GetIO();
    // ... rest of the event handling logic
}