o3de/Code/Framework/AzFramework/AzFramework/Windowing/WindowBus.h

/*
 * Copyright (c) Contributors to the Open 3D Engine Project. For complete copyright and license terms please see the LICENSE at the root of this distribution.
 * 
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 *
 */
#pragma once

#include <AzCore/Component/ComponentBus.h>
#include <AzCore/EBus/EBus.h>

namespace AzFramework
{
    // These bus interfaces are designed to be used by any system that
    // implements any sort of window that provides a surface that a swapchain can
    // attach to.

    using NativeWindowHandle = void*; 

    //! A simple structure to contain window size.
    struct WindowSize
    {
        WindowSize() = default;

        WindowSize(const uint32_t width, const uint32_t height)
            : m_width(width)
            , m_height(height)
        {}

        uint32_t m_width = 0;
        uint32_t m_height = 0;
    };

    //! Bus for sending requests to any kind of window.
    //! It could be a NativeWindow or an Editor window.
    class WindowRequests
        : public AZ::EBusTraits
    {
    public:
        virtual ~WindowRequests() = default;

        // EBusTraits overrides ...
        static const AZ::EBusAddressPolicy AddressPolicy = AZ::EBusAddressPolicy::ById;
        static const AZ::EBusHandlerPolicy HandlerPolicy = AZ::EBusHandlerPolicy::Single;
        using BusIdType = NativeWindowHandle;

        //! For platforms that support it, set the title of the window.
        virtual void SetWindowTitle(const AZStd::string& title) = 0;

        //! Get the client area size. This is the size that can be rendered to.
        //! On some platforms this may not be the correct size until Activate is called.
        virtual WindowSize GetClientAreaSize() const = 0;

        //! Set the client area size. This is the size that can be rendered to.
        virtual void ResizeClientArea(WindowSize clientAreaSize) = 0;

        //! Get the full screen state of the window.
        //! \return True if the window is currently in full screen, false otherwise.
        virtual bool GetFullScreenState() const = 0;

        //! Set the full screen state of the window.
        //! \param[in] fullScreenState The full screen state to set.
        virtual void SetFullScreenState(bool fullScreenState) = 0;

        //! Can the full screen state of the window be changed/toggled?
        //! \return True if the window can enter/exit full screen, false otherwise.
        virtual bool CanToggleFullScreenState() const = 0;

        //! Toggle the full screen state of the window.
        virtual void ToggleFullScreenState() = 0;

        //! Returns a scalar multiplier representing how dots-per-inch this window has, compared
        //! to a "standard" value of 96, the default for Windows in a DPI unaware setting. This can
        //! be used to scale user interface elements to ensure legibility on high density displays.
        virtual float GetDpiScaleFactor() const = 0;
    };
    using WindowRequestBus = AZ::EBus<WindowRequests>;

    //! Bus for listening for notifications from a window.
    //! It could be a NativeWindow or an Editor window.
    class WindowNotifications
        : public AZ::EBusTraits
    {
    public:
        virtual ~WindowNotifications() = default;

        // EBusTraits overrides ...
        static const AZ::EBusAddressPolicy AddressPolicy = AZ::EBusAddressPolicy::ById;
        static const AZ::EBusHandlerPolicy HandlerPolicy = AZ::EBusHandlerPolicy::Multiple;
        using BusIdType = NativeWindowHandle;

        //! This is called once when the window is Activated and also called if the user resizes the window.
        virtual void OnWindowResized(uint32_t width, uint32_t height) { AZ_UNUSED(width); AZ_UNUSED(height); };

        //! This is called if the window's underyling DPI scaling factor changes.
        virtual void OnDpiScaleFactorChanged(float dpiScaleFactor) { AZ_UNUSED(dpiScaleFactor); }

        //! This is called when the window is deactivated from code or if the user closes the window.
        virtual void OnWindowClosed() {};
    };
    using WindowNotificationBus = AZ::EBus<WindowNotifications>;

    //! Bus used by the NativeWindow class to send exclusive full screen related requests to the renderer.
    //! 
    //! This is currently only needed if the Windows DX12 renderer does not support tearing, in which case
    //! the renderer will connect to this bus and assume responsibility for maintaining and transitioning
    //! the full screen state of the corresponding NativeWindowHandle. On platforms where full screen state
    //! is handled exclusively by AzFramework::NativeWindow (eg. Mac) this will never be used, and nor will
    //! it ever be used for platforms that cannot perform full screen transitions at all (eg. iOS/Android).
    //! 
    //! Do not call these directly, use the WindowRequests bus instead to get or set the full screen state.
    class ExclusiveFullScreenRequests
        : public AZ::EBusTraits
    {
    public:
        virtual ~ExclusiveFullScreenRequests() = default;

        // EBusTraits overrides ...
        static const AZ::EBusAddressPolicy AddressPolicy = AZ::EBusAddressPolicy::ById;
        static const AZ::EBusHandlerPolicy HandlerPolicy = AZ::EBusHandlerPolicy::Single;
        using BusIdType = NativeWindowHandle;

        //! This will be called when the NativeWindow needs to know whether the renderer prefers to use exclusive full screen mode.
        //!
        //! Do not call directly, use WindowRequests::GetFullScreenState instead to get the current full screen state of a window.
        //!
        //! \return True if the renderer prefers to use their exclusive full screen mode, false otherwise.
        virtual bool IsExclusiveFullScreenPreferred() const { return false; }

        //! This will be called when the full screen state of a NativeWindow is requested using WindowRequests::GetFullScreenState,
        //! but only if the renderer prefers to use their exclusive full screen mode (ie. IsExclusiveFullScreenPreferred() == true).
        //!
        //! Do not call directly, use WindowRequests::GetFullScreenState instead to get the current full screen state of a window.
        //!
        //! \return True if the renderer prefers to use their exclusive full screen mode and it is currently true, false otherwise.
        virtual bool GetExclusiveFullScreenState() const { return false; }

        //! This will be called when the full screen state of a NativeWindow is set using WindowRequests::SetFullScreenState,
        //! but only if the renderer prefers to use exclusive full screen mode (ie. IsExclusiveFullScreenPreferred() == true).
        //!
        //! Do not call directly, use WindowRequests::GetFullScreenState instead to set the full screen state of a window.
        //!
        //! \param[in] fullScreenState The full screen state that was passed to WindowRequests::SetFullScreenState.
        //! \return True if the renderer prefers to use exclusive full screen mode and a transition happened, false otherwise.
        virtual bool SetExclusiveFullScreenState([[maybe_unused]]bool fullScreenState) { return false; }
    };
    using ExclusiveFullScreenRequestBus = AZ::EBus<ExclusiveFullScreenRequests>;

    //! The WindowSystemRequestBus is a broadcast bus for sending requests to the window system.
    class WindowSystemRequests
        : public AZ::EBusTraits
    {
    public:
        virtual ~WindowSystemRequests() = default;

        // EBusTraits overrides ...
        static const AZ::EBusAddressPolicy AddressPolicy = AZ::EBusAddressPolicy::Single;
        static const AZ::EBusHandlerPolicy HandlerPolicy = AZ::EBusHandlerPolicy::Single;

        //! Get the window handle for the default window
        virtual NativeWindowHandle GetDefaultWindowHandle() = 0;
    };
    using WindowSystemRequestBus = AZ::EBus<WindowSystemRequests>;

    //! The WindowSystemNotificationBus is used to broadcast an event whenever a new window is created.
    class WindowSystemNotifications
        : public AZ::EBusTraits
    {
    public:
        virtual ~WindowSystemNotifications() = default;

        // EBusTraits overrides ...
        static const AZ::EBusAddressPolicy AddressPolicy = AZ::EBusAddressPolicy::Single;
        static const AZ::EBusHandlerPolicy HandlerPolicy = AZ::EBusHandlerPolicy::Multiple;

        //! A notification that a new window was created with the given window ID
        virtual void OnWindowCreated(NativeWindowHandle windowHandle) = 0;
    };
    using WindowSystemNotificationBus = AZ::EBus<WindowSystemNotifications>;
} // namespace AzFramework