/* SPDX-License-Identifier: GPL-2.0-or-later
 * Copyright 2014 Blender Foundation. All rights reserved. */

/** \file
 * \ingroup gpu
 *
 * Interface for accessing GPU-related methods for selection. The semantics will be
 * similar to `glRenderMode(GL_SELECT)` since the goal is to maintain compatibility.
 */

#include <cstdlib>

#include "GPU_debug.h"
#include "GPU_framebuffer.h"
#include "GPU_select.h"
#include "GPU_state.h"

#include "MEM_guardedalloc.h"

#include "BLI_rect.h"

#include "BLI_utildefines.h"
#include "BLI_vector.hh"

#include "gpu_backend.hh"
#include "gpu_query.hh"

#include "gpu_select_private.h"

using namespace blender;
using namespace blender::gpu;

struct GPUSelectQueryState {
  /** Tracks whether a query has been issued so that gpu_load_id can end the previous one. */
  bool query_issued;
  /** GPU queries abstraction. Contains an array of queries. */
  QueryPool *queries;
  /** Array holding the id corresponding id to each query. */
  Vector<uint, QUERY_MIN_LEN> *ids;
  /** Cache on initialization. */
  GPUSelectResult *buffer;
  /** The capacity of the `buffer` array. */
  uint buffer_len;
  /** Mode of operation. */
  eGPUSelectMode mode;
  uint index;
  int oldhits;

  /** Previous state to restore after drawing. */
  int viewport[4];
  int scissor[4];
  eGPUWriteMask write_mask;
  eGPUDepthTest depth_test;
};

static GPUSelectQueryState g_query_state = {false};

void gpu_select_query_begin(GPUSelectResult *buffer,
                            uint buffer_len,
                            const rcti *input,
                            const eGPUSelectMode mode,
                            int oldhits)
{
  GPU_debug_group_begin("Selection Queries");

  g_query_state.query_issued = false;
  g_query_state.buffer = buffer;
  g_query_state.buffer_len = buffer_len;
  g_query_state.mode = mode;
  g_query_state.index = 0;
  g_query_state.oldhits = oldhits;

  g_query_state.ids = new Vector<uint, QUERY_MIN_LEN>();
  g_query_state.queries = GPUBackend::get()->querypool_alloc();
  g_query_state.queries->init(GPU_QUERY_OCCLUSION);

  g_query_state.write_mask = GPU_write_mask_get();
  g_query_state.depth_test = GPU_depth_test_get();
  GPU_scissor_get(g_query_state.scissor);
  GPU_viewport_size_get_i(g_query_state.viewport);

  /* Write to color buffer. Seems to fix issues with selecting alpha blended geom (see T7997). */
  GPU_color_mask(true, true, true, true);

  /* In order to save some fill rate we minimize the viewport using rect.
   * We need to get the region of the viewport so that our geometry doesn't
   * get rejected before the depth test. Should probably cull rect against
   * the viewport but this is a rare case I think */

  int viewport[4] = {
      UNPACK2(g_query_state.viewport), BLI_rcti_size_x(input), BLI_rcti_size_y(input)};

  GPU_viewport(UNPACK4(viewport));
  GPU_scissor(UNPACK4(viewport));
  GPU_scissor_test(false);

  /* occlusion queries operates on fragments that pass tests and since we are interested on all
   * objects in the view frustum independently of their order, we need to disable the depth test */
  if (mode == GPU_SELECT_ALL) {
    /* #glQueries on Windows+Intel drivers only works with depth testing turned on.
     * See T62947 for details */
    GPU_depth_test(GPU_DEPTH_ALWAYS);
    GPU_depth_mask(true);
  }
  else if (mode == GPU_SELECT_NEAREST_FIRST_PASS) {
    GPU_depth_test(GPU_DEPTH_LESS_EQUAL);
    GPU_depth_mask(true);
    GPU_clear_depth(1.0f);
  }
  else if (mode == GPU_SELECT_NEAREST_SECOND_PASS) {
    GPU_depth_test(GPU_DEPTH_EQUAL);
    GPU_depth_mask(false);
  }
}

bool gpu_select_query_load_id(uint id)
{
  if (g_query_state.query_issued) {
    g_query_state.queries->end_query();
  }

  g_query_state.queries->begin_query();
  g_query_state.ids->append(id);
  g_query_state.query_issued = true;

  if (g_query_state.mode == GPU_SELECT_NEAREST_SECOND_PASS) {
    /* Second pass should never run if first pass fails,
     * can read past `buffer_len` in this case. */
    BLI_assert(g_query_state.oldhits != -1);
    if (g_query_state.index < g_query_state.oldhits) {
      if (g_query_state.buffer[g_query_state.index].id == id) {
        g_query_state.index++;
        return true;
      }
      return false;
    }
  }
  return true;
}

uint gpu_select_query_end()
{
  uint hits = 0;
  const uint maxhits = g_query_state.buffer_len;

  if (g_query_state.query_issued) {
    g_query_state.queries->end_query();
  }

  Span<uint> ids = *g_query_state.ids;
  Vector<uint32_t, QUERY_MIN_LEN> result(ids.size());
  g_query_state.queries->get_occlusion_result(result);

  for (int i = 0; i < result.size(); i++) {
    if (result[i] != 0) {
      if (g_query_state.mode != GPU_SELECT_NEAREST_SECOND_PASS) {
        if (hits < maxhits) {
          g_query_state.buffer[hits].depth = 0xFFFF;
          g_query_state.buffer[hits].id = ids[i];
          hits++;
        }
        else {
          hits = -1;
          break;
        }
      }
      else {
        int j;
        /* search in buffer and make selected object first */
        for (j = 0; j < g_query_state.oldhits; j++) {
          if (g_query_state.buffer[j].id == ids[i]) {
            g_query_state.buffer[j].depth = 0;
          }
        }
        break;
      }
    }
  }

  delete g_query_state.queries;
  delete g_query_state.ids;

  GPU_write_mask(g_query_state.write_mask);
  GPU_depth_test(g_query_state.depth_test);
  GPU_viewport(UNPACK4(g_query_state.viewport));

  GPU_debug_group_end();

  return hits;
}