viewport_sprite_sorter_sse4.cpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifdef WITH_SSE
 
#include "stdafx.h"
#include "cpu.h"
#include "smmintrin.h"
#include "viewport_sprite_sorter.h"
#include <forward_list>
#include <map>
#include <stack>
 
#include "safeguards.h"
 
#ifdef POINTER_IS_64BIT
  static_assert((sizeof(ParentSpriteToDraw) % 16) == 0);
# define LOAD_128 _mm_load_si128
#else
# define LOAD_128 _mm_loadu_si128
#endif
 
GNU_TARGET("sse4.1")
void ViewportSortParentSpritesSSE41(ParentSpriteToSortVector *psdv)
{
  if (psdv->size() < 2) return;
 
  const __m128i mask_ptest = _mm_setr_epi8(-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  0,  0,  0,  0);
 
  /* We rely on sprites being, for the most part, already ordered.
   * So we don't need to move many of them and can keep track of their
   * order efficiently by using stack. We always move sprites to the front
   * of the current position, i.e. to the top of the stack.
   * Also use special constants to indicate sorting state without
   * adding extra fields to ParentSpriteToDraw structure.
   */
  const uint32 ORDER_COMPARED = UINT32_MAX; // Sprite was compared but we still need to compare the ones preceding it
  const uint32 ORDER_RETURNED = UINT32_MAX - 1; // Mark sorted sprite in case there are other occurrences of it in the stack
  std::stack<ParentSpriteToDraw *> sprite_order;
  uint32 next_order = 0;
 
  std::forward_list<std::pair<int64, ParentSpriteToDraw *>> sprite_list;  // We store sprites in a list sorted by xmin+ymin
 
  /* Initialize sprite list and order. */
  for (auto p = psdv->rbegin(); p != psdv->rend(); p++) {
    sprite_list.push_front(std::make_pair((*p)->xmin + (*p)->ymin, *p));
    sprite_order.push(*p);
    (*p)->order = next_order++;
  }
 
  sprite_list.sort();
 
  std::vector<ParentSpriteToDraw *> preceding;  // Temporarily stores sprites that precede current and their position in the list
  auto preceding_prev = sprite_list.begin(); // Store iterator in case we need to delete a single preciding sprite
  auto out = psdv->begin();  // Iterator to output sorted sprites
 
  while (!sprite_order.empty()) {
 
    auto s = sprite_order.top();
    sprite_order.pop();
 
    /* Sprite is already sorted, ignore it. */
    if (s->order == ORDER_RETURNED) continue;
 
    /* Sprite was already compared, just need to output it. */
    if (s->order == ORDER_COMPARED) {
      *(out++) = s;
      s->order = ORDER_RETURNED;
      continue;
    }
 
    preceding.clear();
 
    /* We only need sprites with xmin <= s->xmax && ymin <= s->ymax && zmin <= s->zmax
     * So by iterating sprites with xmin + ymin <= s->xmax + s->ymax
     * we get all we need and some more that we filter out later.
     * We don't include zmin into the sum as there are usually more neighbors on x and y than z
     * so including it will actually increase the amount of false positives.
     * Also min coordinates can be > max so using max(xmin, xmax) + max(ymin, ymax)
     * to ensure that we iterate the current sprite as we need to remove it from the list.
     */
    auto ssum = std::max(s->xmax, s->xmin) + std::max(s->ymax, s->ymin);
    auto prev = sprite_list.before_begin();
    auto x = sprite_list.begin();
    while (x != sprite_list.end() && ((*x).first <= ssum)) {
      auto p = (*x).second;
      if (p == s) {
        /* We found the current sprite, remove it and move on. */
        x = sprite_list.erase_after(prev);
        continue;
      }
 
      auto p_prev = prev;
      prev = x++;
 
      /* Check that p->xmin <= s->xmax && p->ymin <= s->ymax && p->zmin <= s->zmax */
      __m128i s_max = LOAD_128((__m128i*) &s->xmax);
      __m128i p_min = LOAD_128((__m128i*) &p->xmin);
      __m128i r1 = _mm_cmplt_epi32(s_max, p_min);
      if (!_mm_testz_si128(mask_ptest, r1))
        continue;
 
      /* Check if sprites overlap, i.e.
       * s->xmin <= p->xmax && s->ymin <= p->ymax && s->zmin <= p->zmax
       */
      __m128i s_min = LOAD_128((__m128i*) &s->xmin);
      __m128i p_max = LOAD_128((__m128i*) &p->xmax);
      __m128i r2 = _mm_cmplt_epi32(p_max, s_min);
      if (_mm_testz_si128(mask_ptest, r2)) {
        /* Use X+Y+Z as the sorting order, so sprites closer to the bottom of
         * the screen and with higher Z elevation, are drawn in front.
         * Here X,Y,Z are the coordinates of the "center of mass" of the sprite,
         * i.e. X=(left+right)/2, etc.
         * However, since we only care about order, don't actually divide / 2
         */
        if (s->xmin + s->xmax + s->ymin + s->ymax + s->zmin + s->zmax <=
            p->xmin + p->xmax + p->ymin + p->ymax + p->zmin + p->zmax) {
          continue;
        }
      }
 
      preceding.push_back(p);
      preceding_prev = p_prev;
    }
 
    if (preceding.empty()) {
      /* No preceding sprites, add current one to the output */
      *(out++) = s;
      s->order = ORDER_RETURNED;
      continue;
    }
 
    /* Optimization for the case when we only have 1 sprite to move. */
    if (preceding.size() == 1) {
      auto p = preceding[0];
      /* We can only output the preceding sprite if there can't be any other sprites preceding it. */
      if (p->xmax <= s->xmax && p->ymax <= s->ymax && p->zmax <= s->zmax) {
        p->order = ORDER_RETURNED;
        s->order = ORDER_RETURNED;
        sprite_list.erase_after(preceding_prev);
        *(out++) = p;
        *(out++) = s;
        continue;
      }
    }
 
    /* Sort all preceding sprites by order and assign new orders in reverse (as original sorter did). */
    std::sort(preceding.begin(), preceding.end(), [](const ParentSpriteToDraw *a, const ParentSpriteToDraw *b) {
      return a->order > b->order;
    });
 
    s->order = ORDER_COMPARED;
    sprite_order.push(s);  // Still need to output so push it back for now
 
    for (auto p: preceding) {
      p->order = next_order++;
      sprite_order.push(p);
    }
  }
}
 
 
bool ViewportSortParentSpritesSSE41Checker()
{
  return HasCPUIDFlag(1, 2, 19);
}
 
#endif /* WITH_SSE */