gui_reorderable_subsystem.h

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#pragma once
 
#include <cstdint>
#include <functional>
#include <vector>
 
#include <gui_core/gui_id.h>
#include <gui_core/gui_base_types.h>
#include <gui_core/elements/gui_element.h>
#include <gui_core/input/gui_pointer_drag.h>
 
namespace tachyon
{

    enum class ReorderDirection : uint8_t { Horizontal, Vertical };

    struct ReorderableDragState
    {
        PointerDrag press;              
        tachyon::int2 cursorLocal{};    
        tachyon::int2 cursorScreen{};   
        bool     isWrapped     = false; 
        tachyon::ID  groupID       = tachyon::ID::Invalid();
        int      draggedIndex   = -1;   
        int      insertionIndex = -1;   
        int      itemCount      = 0;    
        std::vector<tachyon::IntRect> originalRects; 
        std::vector<tachyon::ID> originalIDs;
        ReorderDirection direction = ReorderDirection::Vertical;
        tachyon::IntRect groupRect{};      

        bool IsPressed() const { return press.id != tachyon::ID::Invalid(); }
        bool IsDragging() const { return IsPressed() && press.dragging; }
        tachyon::int2 Offset() const { return cursorLocal - press.pressLocal; }
    };

    struct ReorderableConstructionState
    {
        tachyon::ID groupID         = tachyon::ID::Invalid();
        ReorderDirection direction = ReorderDirection::Vertical;
        bool    isWrapped       = false;
        bool    reorderApplied  = false;   
        std::function<void(int, int)>             onReorder;   
        std::function<void(int, tachyon::int2)>       onDragOut;
        std::function<void(int, tachyon::int2)>       dragVisualizer;
        int                          nextItemIndex = 0;
        tachyon::ElementRef              groupRef      = tachyon::ElementRef::Invalid();
        tachyon::ID                      dropAreaID    = tachyon::ID::Invalid();
        std::vector<tachyon::ElementRef> itemRefs;
        int keyboardFrom = -1;
        int keyboardStep = 0;
    };

    struct ReorderableFocusFollow
    {
        tachyon::ID           groupID = tachyon::ID::Invalid();
        int                   toSlot  = -1;
        tachyon::ID           focusID = tachyon::ID::Invalid();
        std::vector<uint32_t> path;   
    };
 
    class FramePipeline;
    struct FrameContext;

    class ReorderableSubsystem
    {
    public:
        explicit ReorderableSubsystem(FramePipeline& frame);
 
        ReorderableDragState&         Drag()         { return m_drag; }           
        ReorderableConstructionState& Construction() { return m_construction; }   
        ReorderableFocusFollow&       FocusFollow()  { return m_focusFollow; }    

        bool IsBalanced() const { return m_construction.groupID == tachyon::ID::Invalid(); }
 
    private:
        void OnPreConstruct(FrameContext& ctx);
        void OnEndFrame();
 
        ReorderableDragState         m_drag{};
        ReorderableConstructionState m_construction{};
        ReorderableFocusFollow       m_focusFollow{};
    };
}