src/core/atlas.cpp

// FCS Glass - src/core/atlas.cpp. See atlas.h.

#include "core/atlas.h"

namespace fcs {
namespace core {

ShelfPacker::ShelfPacker(int width, int max_height, int padding)
    : width_(width < 1 ? 1 : width),
      max_height_(max_height < 1 ? 1 : max_height),
      padding_(padding < 0 ? 0 : padding) {}

void ShelfPacker::Reset() {
  shelves_.clear();
  next_y_ = 0;
}

void ShelfPacker::SetMaxHeight(int max_height) {
  if (max_height > max_height_) max_height_ = max_height;
}

bool ShelfPacker::Pack(int w, int h, AtlasRect* out) {
  if (out == nullptr) return false;
  *out = AtlasRect();
  if (w <= 0 || h <= 0) return true;   // nothing to store

  // Compare before adding the padding so a huge w cannot overflow.
  if (w > width_ - 2 * padding_ || h > max_height_ - 2 * padding_) return false;
  const int ow = w + 2 * padding_;
  const int oh = h + 2 * padding_;

  // Best fit: the shortest existing shelf that is tall enough and has room.
  int best = -1;
  for (int i = 0; i < static_cast<int>(shelves_.size()); ++i) {
    const Shelf& s = shelves_[static_cast<size_t>(i)];
    if (s.h >= oh && s.x + ow <= width_ &&
        (best < 0 || s.h < shelves_[static_cast<size_t>(best)].h)) {
      best = i;
    }
  }

  int cell_x = 0;
  int cell_y = 0;
  if (best >= 0) {
    Shelf& s = shelves_[static_cast<size_t>(best)];
    cell_x = s.x;
    cell_y = s.y;
    s.x += ow;
  } else {
    if (next_y_ + oh > max_height_) return false;
    Shelf s;
    s.y = next_y_;
    s.h = oh;
    s.x = ow;
    shelves_.push_back(s);
    cell_x = 0;
    cell_y = next_y_;
    next_y_ += oh;
  }

  out->x = cell_x + padding_;
  out->y = cell_y + padding_;
  out->w = w;
  out->h = h;
  return true;
}

}  // namespace core
}  // namespace fcs