GuiLayoutSolver.h

/****************************************************************************
 * libgui
 * Daryl Borth 2026
 * GuiLayoutSolver.h
 *
 * Platform-agnostic layout math: given the natural sizes of some items and a
 * few rules, work out where each one goes. The layout containers (GuiRow,
 * GuiColumn, GuiGrid, GuiOverlay) are thin adapters that feed GuiElements to
 * these functions and apply the answers. Everything here is plain numbers,
 * so it is tested on a host machine.
 *
 * Coordinates are relative to the container's top-left corner.
 ***************************************************************************/
#pragma once
#include <vector>
#include "GuiGeometry.h"

enum class LAYOUT_ALIGN {
    START,     
    CENTRE,     
    END,     
    STRETCH      
};

enum class LAYOUT_JUSTIFY {
    START,         
    CENTRE,         
    END,         
    SPACE_BETWEEN  
};

struct GuiInsets {
    float left, top, right, bottom;
    GuiInsets(float all = 0.0f) : left(all), top(all), right(all), bottom(all) {}
    GuiInsets(float horizontal, float vertical) : left(horizontal), top(vertical), right(horizontal), bottom(vertical) {}
    GuiInsets(float l, float t, float r, float b) : left(l), top(t), right(r), bottom(b) {}
};

struct GuiStackItem {
    float w, h;                
    float grow;             
    bool useContainerAlign;    
    LAYOUT_ALIGN align;        
    GuiStackItem() : w(0), h(0), grow(0), useContainerAlign(true), align(LAYOUT_ALIGN::START) {}
};

struct GuiStackSpec {
    bool vertical;          
    GuiInsets padding;
    float spacing;           
    float fixedW, fixedH; 
    LAYOUT_JUSTIFY justify;
    LAYOUT_ALIGN alignItems;
    GuiStackSpec() : vertical(false), spacing(0), fixedW(0), fixedH(0), justify(LAYOUT_JUSTIFY::START), alignItems(LAYOUT_ALIGN::START) {}
};

struct GuiLayoutResult {
    float width, height;
    std::vector<GuiRect> rects;
    GuiLayoutResult() : width(0), height(0) {}
};

GuiLayoutResult GuiSolveStack(const GuiStackSpec& spec, const std::vector<GuiStackItem>& items);

struct GuiGridItem {
    float w, h;
    LAYOUT_ALIGN alignH, alignV;  
    GuiGridItem() : w(0), h(0), alignH(LAYOUT_ALIGN::START), alignV(LAYOUT_ALIGN::START) {}
};

struct GuiGridSpec {
    int columns;
    GuiInsets padding;
    float spacingX, spacingY;
    float fixedW, fixedH; 
    GuiGridSpec() : columns(1), spacingX(0), spacingY(0), fixedW(0), fixedH(0) {}
};

GuiLayoutResult GuiSolveGrid(const GuiGridSpec& spec, const std::vector<GuiGridItem>& items);

struct GuiOverlayItem {
    float w, h;
    LAYOUT_ALIGN alignH, alignV;
    bool background;      
    GuiOverlayItem() : w(0), h(0), alignH(LAYOUT_ALIGN::CENTRE), alignV(LAYOUT_ALIGN::CENTRE), background(false) {}
};

struct GuiOverlaySpec {
    GuiInsets padding;
    float fixedW, fixedH; 
    GuiOverlaySpec() : fixedW(0), fixedH(0) {}
};

GuiLayoutResult GuiSolveOverlay(const GuiOverlaySpec& spec, const std::vector<GuiOverlayItem>& items);

enum class NAV_DIR { LEFT, RIGHT, UP, DOWN };

struct GuiNavItem {
    GuiRect r;          
    bool selectable;
};

int GuiNavigate(const std::vector<GuiNavItem>& items, int current, NAV_DIR dir);