text: // [DEAR IMGUI]
  // This is a slightly modified version of stb_rect_pack.h 1.00.
  // Those changes would need to be pushed into nothings/stb:
  // - Added STBRP__CDECL
  // Grep for [DEAR IMGUI] to find the changes.
  
  // stb_rect_pack.h - v1.00 - public domain - rectangle packing
  // Sean Barrett 2014
  //
  // Useful for e.g. packing rectangular textures into an atlas.
  // Does not do rotation.
  //
  // Not necessarily the awesomest packing method, but better than
  // the totally naive one in stb_truetype (which is primarily what
  // this is meant to replace).
  //
  // Has only had a few tests run, may have issues.
  //
  // More docs to come.
  //
  // No memory allocations; uses qsort() and assert() from stdlib.
  // Can override those by defining STBRP_SORT and STBRP_ASSERT.
  //
  // This library currently uses the Skyline Bottom-Left algorithm.
  //
  // Please note: better rectangle packers are welcome! Please
  // implement them to the same API, but with a different init
  // function.
  //
  // Credits
  //
  //  Library
  //    Sean Barrett
  //  Minor features
  //    Martins Mozeiko
  //    github:IntellectualKitty
  //    
  //  Bugfixes / warning fixes
  //    Jeremy Jaussaud
  //    Fabian Giesen
  //
  // Version history:
  //
  //     1.00  (2019-02-25)  avoid small space waste; gracefully fail too-wide rectangles
  //     0.99  (2019-02-07)  warning fixes
  //     0.11  (2017-03-03)  return packing success/fail result
  //     0.10  (2016-10-25)  remove cast-away-const to avoid warnings
  //     0.09  (2016-08-27)  fix compiler warnings
  //     0.08  (2015-09-13)  really fix bug with empty rects (w=0 or h=0)
  //     0.07  (2015-09-13)  fix bug with empty rects (w=0 or h=0)
  //     0.06  (2015-04-15)  added STBRP_SORT to allow replacing qsort
  //     0.05:  added STBRP_ASSERT to allow replacing assert
  //     0.04:  fixed minor bug in STBRP_LARGE_RECTS support
  //     0.01:  initial release
  //
  // LICENSE
  //
  //   See end of file for license information.
  
  //////////////////////////////////////////////////////////////////////////////
  //
  //       INCLUDE SECTION
  //
  
  #ifndef STB_INCLUDE_STB_RECT_PACK_H
  #define STB_INCLUDE_STB_RECT_PACK_H
  
  #define STB_RECT_PACK_VERSION  1
  
  #ifdef STBRP_STATIC
  #define STBRP_DEF static
  #else
  #define STBRP_DEF extern
  #endif
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  typedef struct stbrp_context stbrp_context;
  typedef struct stbrp_node    stbrp_node;
  typedef struct stbrp_rect    stbrp_rect;
  
  #ifdef STBRP_LARGE_RECTS
  typedef int            stbrp_coord;
  #else
  typedef unsigned short stbrp_coord;
  #endif
  
  STBRP_DEF int stbrp_pack_rects (stbrp_context *context, stbrp_rect *rects, int num_rects);
  // Assign packed locations to rectangles. The rectangles are of type
  // 'stbrp_rect' defined below, stored in the array 'rects', and there
  // are 'num_rects' many of them.
  //
  // Rectangles which are successfully packed have the 'was_packed' flag
  // set to a non-zero value and 'x' and 'y' store the minimum location
  // on each axis (i.e. bottom-left in cartesian coordinates, top-left
  // if you imagine y increasing downwards). Rectangles which do not fit
  // have the 'was_packed' flag set to 0.
  //
  // You should not try to access the 'rects' array from another thread
  // while this function is running, as the function temporarily reorders
  // the array while it executes.
  //
  // To pack into another rectangle, you need to call stbrp_init_target
  // again. To continue packing into the same rectangle, you can call
  // this function again. Calling this multiple times with multiple rect
  // arrays will probably produce worse packing results than calling it
  // a single time with the full rectangle array, but the option is
  // available.
  //
  // The function returns 1 if all of the rectangles were successfully
  // packed and 0 otherwise.
  
  struct stbrp_rect
  {
     // reserved for your use:
     int            id;
  
     // input:
     stbrp_coord    w, h;
  
     // output:
     stbrp_coord    x, y;
     int            was_packed;  // non-zero if valid packing
  
  }; // 16 bytes, nominally
  
  
  STBRP_DEF void stbrp_init_target (stbrp_context *context, int width, int height, stbrp_node *nodes, int num_nodes);
  // Initialize a rectangle packer to:
  //    pack a rectangle that is 'width' by 'height' in dimensions
  //    using temporary storage provided by the array 'nodes', which is 'num_nodes' long
  //
  // You must call this function every time you start packing into a new target.
  //
  // There is no "shutdown" function. The 'nodes' memory must stay valid for
  // the following stbrp_pack_rects() call (or calls), but can be freed after
  // the call (or calls) finish.
  //
  // Note: to guarantee best results, either:
  //       1. make sure 'num_nodes' >= 'width'
  //   or  2. call stbrp_allow_out_of_mem() defined below with 'allow_out_of_mem = 1'
  //
  // If you don't do either of the above things, widths will be quantized to multiples
  // of small integers to guarantee the algorithm doesn't run out of temporary storage.
  //
  // If you do #2, then the non-quantized algorithm will be used, but the algorithm
  // may run out of temporary storage and be unable to pack some rectangles.
  
  STBRP_DEF void stbrp_setup_allow_out_of_mem (stbrp_context *context, int allow_out_of_mem);
  // Optionally call this function after init but before doing any packing to
  // change the handling of the out-of-temp-memory scenario, described above.
  // If you call init again, this will be clear to the default (false).
  
  
  STBRP_DEF void stbrp_setup_heuristic (stbrp_context *context, int heuristic);
  // Optionally select which packing heuristic the library should use. Different
  // heuristics will produce better/worse results for different data sets.
  // If you call init again, this will be clear to the default.
  
  enum
  {
     STBRP_HEURISTIC_Skyline_default=0,
     STBRP_HEURISTIC_Skyline_BL_sortHeight = STBRP_HEURISTIC_Skyline_default,
     STBRP_HEURISTIC_Skyline_BF_sortHeight
  };
  
  
  //////////////////////////////////////////////////////////////////////////////
  //
  // the details of the following structures don't matter to you, but they must
  // be visible so you can handle the memory allocations for them
  
  struct stbrp_node
  {
     stbrp_coord  x,y;
     stbrp_node  *next;
  };
  
  struct stbrp_context
  {
     int width;
     int height;
     int align;
     int init_mode;
     int heuristic;
     int num_nodes;
     stbrp_node *active_head;
     stbrp_node *free_head;
     stbrp_node extra[2]; // we allocate two extra nodes so optimal user-node-count is 'width' not 'width+2'
  };
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif
  
  //////////////////////////////////////////////////////////////////////////////
  //
  //     IMPLEMENTATION SECTION
  //
  
  #ifdef STB_RECT_PACK_IMPLEMENTATION
  #ifndef STBRP_SORT
  #include <stdlib.h>
  #define STBRP_SORT qsort
  #endif
  
  #ifndef STBRP_ASSERT
  #include <assert.h>
  #define STBRP_ASSERT assert
  #endif
  
  // [DEAR IMGUI] Added STBRP__CDECL
  #ifdef _MSC_VER
  #define STBRP__NOTUSED(v)  (void)(v)
  #define STBRP__CDECL __cdecl
  #else
  #define STBRP__NOTUSED(v)  (void)sizeof(v)
  #define STBRP__CDECL
  #endif
  
  enum
  {
     STBRP__INIT_skyline = 1
  };
  
  STBRP_DEF void stbrp_setup_heuristic(stbrp_context *context, int heuristic)
  {
     switch (context->init_mode) {
        case STBRP__INIT_skyline:
           STBRP_ASSERT(heuristic == STBRP_HEURISTIC_Skyline_BL_sortHeight || heuristic == STBRP_HEURISTIC_Skyline_BF_sortHeight);
           context->heuristic = heuristic;
           break;
        default:
           STBRP_ASSERT(0);
     }
  }
  
  STBRP_DEF void stbrp_setup_allow_out_of_mem(stbrp_context *context, int allow_out_of_mem)
  {
     if (allow_out_of_mem)
        // if it's ok to run out of memory, then don't bother aligning them;
        // this gives better packing, but may fail due to OOM (even though
        // the rectangles easily fit). @TODO a smarter approach would be to only
        // quantize once we've hit OOM, then we could get rid of this parameter.
        context->align = 1;
     else {
        // if it's not ok to run out of memory, then quantize the widths
        // so that num_nodes is always enough nodes.
        //
        // I.e. num_nodes * align >= width
        //                  align >= width / num_nodes
        //                  align = ceil(width/num_nodes)
  
        context->align = (context->width + context->num_nodes-1) / context->num_nodes;
     }
  }
  
  STBRP_DEF void stbrp_init_target(stbrp_context *context, int width, int height, stbrp_node *nodes, int num_nodes)
  {
     int i;
  #ifndef STBRP_LARGE_RECTS
     STBRP_ASSERT(width <= 0xffff && height <= 0xffff);
  #endif
  
     for (i=0; i < num_nodes-1; ++i)
        nodes[i].next = &nodes[i+1];
     nodes[i].next = NULL;
     context->init_mode = STBRP__INIT_skyline;
     context->heuristic = STBRP_HEURISTIC_Skyline_default;
     context->free_head = &nodes[0];
     context->active_head = &context->extra[0];
     context->width = width;
     context->height = height;
     context->num_nodes = num_nodes;
     stbrp_setup_allow_out_of_mem(context, 0);
  
     // node 0 is the full width, node 1 is the sentinel (lets us not store width explicitly)
     context->extra[0].x = 0;
     context->extra[0].y = 0;
     context->extra[0].next = &context->extra[1];
     context->extra[1].x = (stbrp_coord) width;
  #ifdef STBRP_LARGE_RECTS
     context->extra[1].y = (1<<30);
  #else
     context->extra[1].y = 65535;
  #endif
     context->extra[1].next = NULL;
  }
  
  // find minimum y position if it starts at x1
  static int stbrp__skyline_find_min_y(stbrp_context *c, stbrp_node *first, int x0, int width, int *pwaste)
  {
     stbrp_node *node = first;
     int x1 = x0 + width;
     int min_y, visited_width, waste_area;
  
     STBRP__NOTUSED(c);
  
     STBRP_ASSERT(first->x <= x0);
  
     #if 0
     // skip in case we're past the node
     while (node->next->x <= X_AT_0)
        ++node;
     #else
     STBRP_ASSERT(node->next->x > x0); // we ended up handling this in the caller for efficiency
     #endif
  
     STBRP_ASSERT(node->x <= x0);
  
     min_y = 0;
     waste_area = 0;
     visited_width = 0;
     while (node->x < x1) {
        if (node->y > min_y) {
           // raise min_y higher.
           // we've accounted for all waste up to min_y,
           // but we'll now add more waste for everything we've visted
           waste_area += visited_width * (node->y - min_y);
           min_y = node->y;
           // the first time through, visited_width might be reduced
           if (node->x < x0)
              visited_width += node->next->x - x0;
           else
              visited_width += node->next->x - node->x;
        } else {
           // add waste area
           int under_width = node->next->x - node->x;
           if (under_width + visited_width > width)
              under_width = width - visited_width;
           waste_area += under_width * (min_y - node->y);
           visited_width += under_width;
        }
        node = node->next;
     }
  
     *pwaste = waste_area;
     return min_y;
  }
  
  typedef struct
  {
     int x,y;
     stbrp_node **prev_link;
  } stbrp__findresult;
  
  static stbrp__findresult stbrp__skyline_find_best_pos(stbrp_context *c, int width, int height)
  {
     int best_waste = (1<<30), best_x, best_y = (1 << 30);
     stbrp__findresult fr;
     stbrp_node **prev, *node, *tail, **best = NULL;
  
     // align to multiple of c->align
     width = (width + c->align - 1);
     width -= width % c->align;
     STBRP_ASSERT(width % c->align == 0);
  
     // if it can't possibly fit, bail immediately
     if (width > c->width || height > c->height) {
        fr.prev_link = NULL;
        fr.x = fr.y = 0;
        return fr;
     }
  
     node = c->active_head;
     prev = &c->active_head;
     while (node->x + width <= c->width) {
        int y,waste;
        y = stbrp__skyline_find_min_y(c, node, node->x, width, &waste);
        if (c->heuristic == STBRP_HEURISTIC_Skyline_BL_sortHeight) { // actually just want to test BL
           // bottom left
           if (y < best_y) {
              best_y = y;
              best = prev;
           }
        } else {
           // best-fit
           if (y + height <= c->height) {
              // can only use it if it first vertically
              if (y < best_y || (y == best_y && waste < best_waste)) {
                 best_y = y;
                 best_waste = waste;
                 best = prev;
              }
           }
        }
        prev = &node->next;
        node = node->next;
     }
  
     best_x = (best == NULL) ? 0 : (*best)->x;
  
     // if doing best-fit (BF), we also have to try aligning right edge to each node position
     //
     // e.g, if fitting
     //
     //     ____________________
     //    |____________________|
     //
     //            into
     //
     //   |                         |
     //   |             ____________|
     //   |____________|
     //
     // then right-aligned reduces waste, but bottom-left BL is always chooses left-aligned
     //
     // This makes BF take about 2x the time
  
     if (c->heuristic == STBRP_HEURISTIC_Skyline_BF_sortHeight) {
        tail = c->active_head;
        node = c->active_head;
        prev = &c->active_head;
        // find first node that's admissible
        while (tail->x < width)
           tail = tail->next;
        while (tail) {
           int xpos = tail->x - width;
           int y,waste;
           STBRP_ASSERT(xpos >= 0);
           // find the left position that matches this
           while (node->next->x <= xpos) {
              prev = &node->next;
              node = node->next;
           }
           STBRP_ASSERT(node->next->x > xpos && node->x <= xpos);
           y = stbrp__skyline_find_min_y(c, node, xpos, width, &waste);
           if (y + height <= c->height) {
              if (y <= best_y) {
                 if (y < best_y || waste < best_waste || (waste==best_waste && xpos < best_x)) {
                    best_x = xpos;
                    STBRP_ASSERT(y <= best_y);
                    best_y = y;
                    best_waste = waste;
                    best = prev;
                 }
              }
           }
           tail = tail->next;
        }         
     }
  
     fr.prev_link = best;
     fr.x = best_x;
     fr.y = best_y;
     return fr;
  }
  
  static stbrp__findresult stbrp__skyline_pack_rectangle(stbrp_context *context, int width, int height)
  {
     // find best position according to heuristic
     stbrp__findresult res = stbrp__skyline_find_best_pos(context, width, height);
     stbrp_node *node, *cur;
  
     // bail if:
     //    1. it failed
     //    2. the best node doesn't fit (we don't always check this)
     //    3. we're out of memory
     if (res.prev_link == NULL || res.y + height > context->height || context->free_head == NULL) {
        res.prev_link = NULL;
        return res;
     }
  
     // on success, create new node
     node = context->free_head;
     node->x = (stbrp_coord) res.x;
     node->y = (stbrp_coord) (res.y + height);
  
     context->free_head = node->next;
  
     // insert the new node into the right starting point, and
     // let 'cur' point to the remaining nodes needing to be
     // stiched back in
  
     cur = *res.prev_link;
     if (cur->x < res.x) {
        // preserve the existing one, so start testing with the next one
        stbrp_node *next = cur->next;
        cur->next = node;
        cur = next;
     } else {
        *res.prev_link = node;
     }
  
     // from here, traverse cur and free the nodes, until we get to one
     // that shouldn't be freed
     while (cur->next && cur->next->x <= res.x + width) {
        stbrp_node *next = cur->next;
        // move the current node to the free list
        cur->next = context->free_head;
        context->free_head = cur;
        cur = next;
     }
  
     // stitch the list back in
     node->next = cur;
  
     if (cur->x < res.x + width)
        cur->x = (stbrp_coord) (res.x + width);
  
  #ifdef _DEBUG
     cur = context->active_head;
     while (cur->x < context->width) {
        STBRP_ASSERT(cur->x < cur->next->x);
        cur = cur->next;
     }
     STBRP_ASSERT(cur->next == NULL);
  
     {
        int count=0;
        cur = context->active_head;
        while (cur) {
           cur = cur->next;
           ++count;
        }
        cur = context->free_head;
        while (cur) {
           cur = cur->next;
           ++count;
        }
        STBRP_ASSERT(count == context->num_nodes+2);
     }
  #endif
  
     return res;
  }
  
  // [DEAR IMGUI] Added STBRP__CDECL
  static int STBRP__CDECL rect_height_compare(const void *a, const void *b)
  {
     const stbrp_rect *p = (const stbrp_rect *) a;
     const stbrp_rect *q = (const stbrp_rect *) b;
     if (p->h > q->h)
        return -1;
     if (p->h < q->h)
        return  1;
     return (p->w > q->w) ? -1 : (p->w < q->w);
  }
  
  // [DEAR IMGUI] Added STBRP__CDECL
  static int STBRP__CDECL rect_original_order(const void *a, const void *b)
  {
     const stbrp_rect *p = (const stbrp_rect *) a;
     const stbrp_rect *q = (const stbrp_rect *) b;
     return (p->was_packed < q->was_packed) ? -1 : (p->was_packed > q->was_packed);
  }
  
  #ifdef STBRP_LARGE_RECTS
  #define STBRP__MAXVAL  0xffffffff
  #else
  #define STBRP__MAXVAL  0xffff
  #endif
  
  STBRP_DEF int stbrp_pack_rects(stbrp_context *context, stbrp_rect *rects, int num_rects)
  {
     int i, all_rects_packed = 1;
  
     // we use the 'was_packed' field internally to allow sorting/unsorting
     for (i=0; i < num_rects; ++i) {
        rects[i].was_packed = i;
     }
  
     // sort according to heuristic
     STBRP_SORT(rects, num_rects, sizeof(rects[0]), rect_height_compare);
  
     for (i=0; i < num_rects; ++i) {
        if (rects[i].w == 0 || rects[i].h == 0) {
           rects[i].x = rects[i].y = 0;  // empty rect needs no space
        } else {
           stbrp__findresult fr = stbrp__skyline_pack_rectangle(context, rects[i].w, rects[i].h);
           if (fr.prev_link) {
              rects[i].x = (stbrp_coord) fr.x;
              rects[i].y = (stbrp_coord) fr.y;
           } else {
              rects[i].x = rects[i].y = STBRP__MAXVAL;
           }
        }
     }
  
     // unsort
     STBRP_SORT(rects, num_rects, sizeof(rects[0]), rect_original_order);
  
     // set was_packed flags and all_rects_packed status
     for (i=0; i < num_rects; ++i) {
        rects[i].was_packed = !(rects[i].x == STBRP__MAXVAL && rects[i].y == STBRP__MAXVAL);
        if (!rects[i].was_packed)
           all_rects_packed = 0;
     }
  
     // return the all_rects_packed status
     return all_rects_packed;
  }
  #endif
  
  /*
  ------------------------------------------------------------------------------
  This software is available under 2 licenses -- choose whichever you prefer.
  ------------------------------------------------------------------------------
  ALTERNATIVE A - MIT License
  Copyright (c) 2017 Sean Barrett
  Permission is hereby granted, free of charge, to any person obtaining a copy of 
  this software and associated documentation files (the "Software"), to deal in 
  the Software without restriction, including without limitation the rights to 
  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies 
  of the Software, and to permit persons to whom the Software is furnished to do 
  so, subject to the following conditions:
  The above copyright notice and this permission notice shall be included in all 
  copies or substantial portions of the Software.
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
  SOFTWARE.
  ------------------------------------------------------------------------------
  ALTERNATIVE B - Public Domain (www.unlicense.org)
  This is free and unencumbered software released into the public domain.
  Anyone is free to copy, modify, publish, use, compile, sell, or distribute this 
  software, either in source code form or as a compiled binary, for any purpose, 
  commercial or non-commercial, and by any means.
  In jurisdictions that recognize copyright laws, the author or authors of this 
  software dedicate any and all copyright interest in the software to the public 
  domain. We make this dedication for the benefit of the public at large and to 
  the detriment of our heirs and successors. We intend this dedication to be an 
  overt act of relinquishment in perpetuity of all present and future rights to 
  this software under copyright law.
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
  AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN 
  ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION 
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  ------------------------------------------------------------------------------
  */
  