MRUIRectAllocator.h

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#pragma once
 
#include "exports.h"
#include "MRMesh/MRBox.h"
#include "MRMesh/MRHash.h"
#include "MRMesh/MRphmap.h"
#include "MRMesh/MRVector2.h"
#include "MRMesh/MRViewportId.h"
 
#include <imgui.h>
 
namespace MR::UI
{
 
// A generic rect allocator.
// Given a set of rects and a target rect, finds the closest free rect next to the target (using dijkstra's algorithm).
// The class can be reused multiple times to avoid repeated heap allocation, it doesn't store any state other than memory pools.
// For optimal results you should bring your own AABB tree (see `FindPotentiallyOverlappingRects`) below,
// but in simple cases you can get away with a flat list.
class RectAllocator
{
public:
    MRVIEWER_API RectAllocator();
 
    struct FindFreeRectResult
    {
        Box2f rect;
        bool ok = true; // False if no free space for this rect.
        [[nodiscard]] explicit operator bool() const { return ok; }
    };
 
    // Given an input rect, this function must find all POTENTIALLY overlapping rects ("overlapping" means according to `rectRectOverlap()`).
    // `name` is only useful for debugging.
    using FindPotentiallyOverlappingRects = std::function<void( Box2f target, std::function<void( const char* name, Box2f box )> overlaps )>;
 
    // Finds a free rectangle of the specified size, as close as possible to the specified position.
    // On failure, returns `.ok == false` and returns the input rect unchanged.
    [[nodiscard]] MRVIEWER_API FindFreeRectResult findFreeRect(
        Box2f preferredRect,
        // The outer bounds that we try to fit the rect into. The input rect doesn't need to be in bounds,
        // but we will not move it more out of bounds than it already is.
        Box2f preferredBounds,
        // Given any rect, this must return all existing rects potentially overlapping with it.
        FindPotentiallyOverlappingRects findOverlaps,
        // This sets the preference for X and Y axes. Larger number = less likely to shift over that axis.
        ImVec2 axisWeights = ImVec2( 1, 1 )
    );
 
    // Checks if two rects overlap.
    // We can't use `.intersects()` here because we want `.max` to be exclusive, while `.intersects()` treats both bounds as inclusive.
    [[nodiscard]] static bool rectRectOverlap( Box2f a, Box2f b )
    {
        return a.max.x > b.min.x && a.min.x < b.max.x && a.max.y > b.min.y && a.min.y < b.max.y;
    }
 
private:
    // Maps coords to cost.
    phmap::flat_hash_map<Vector2f, float> visitedCoords;
 
    struct CoordsToVisit
    {
        Vector2f pos;
        float cost = 0;
        std::array<float, 4> overlapWithBounds;
    };
    std::vector<CoordsToVisit> coordsToVisitHeap;
};
 
// A rect allocator specifically for ImGui windows.
class WindowRectAllocator : public RectAllocator
{
public:
    // Call this before drawing a window.
    // `expectedWindowName` must match the window name.
    // The remaining parameters are forwarded to `ImGui::SetNextWindowPos()`, expect for one time where we find a free rect and use it instead.
    // `cond` must not be `ImGuiCond_Always` (aka 0), in that case we just forward the arguments and don't try to find a rect.
    // We automatically avoid all windows with `[rect_allocator_ignore]` anywhere after `##` in the name.
    MRVIEWER_API void setFreeNextWindowPos( const char* expectedWindowName, ImVec2 defaultPos, ImGuiCond cond = ImGuiCond_Appearing, ImVec2 pivot = ImVec2() );
 
private:
    int lastFrameCount_ = -1;
 
    enum class AllocationState
    {
        None, // This window wasn't yet drawn during this frame. If it's not drawn until the end of frame, it will be deleted from this map.
        Requested, // This window has just appeared and a free position will be selected for it in the next frame
        Set // This window has set position and was already drawn in this frame
    };
 
    struct WindowEntry
    {
        AllocationState state_{ AllocationState::None };
    };
    phmap::flat_hash_map<std::string, WindowEntry> windows_;
};
[[nodiscard]] MRVIEWER_API WindowRectAllocator& getDefaultWindowRectAllocator();
 
// A rect allocator for labels.
class LabelRectAllocator : public RectAllocator
{
public:
    // Call this every frame to maintain a rectangle. Using the same ID more than once per frame triggers an assertion.
    // Returns the free position closest to `pos`.
    // Separate label lists are maintained per viewport.
    // If `forceExactPosition == true`, the input position is returned unchanged, but the rect is still added to the internal list to push away other rects.
    MRVIEWER_API ImVec2 createRect( ViewportId viewportId, std::string id, ImVec2 pos, ImVec2 size, bool forceExactPosition = false );
 
private:
    int lastFrameCount_ = -1;
 
    struct Entry
    {
        Box2f box;
        bool visitedThisFrame = true;
    };
    // The vector uses viewport indices.
    std::vector<phmap::flat_hash_map<std::string, Entry>> entries_;
};
[[nodiscard]] MRVIEWER_API LabelRectAllocator& getDefaultLabelRectAllocator();
 
}