/* SPDX-FileCopyrightText: 2016 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

/** \file
 * \ingroup draw
 */

/**
 * DRW Instance Data Manager
 * This is a special memory manager that keeps memory blocks ready to send as VBO data in one
 * continuous allocation. This way we avoid feeding #gpu::Batch each instance data one by one and
 * unnecessary `memcpy`. Since we lose which memory block was used each #DRWShadingGroup we need to
 * redistribute them in the same order/size to avoid to realloc each frame. This is why
 * #DRWInstanceDatas are sorted in a list for each different data size.
 */

#include "draw_instance_data.hh"

#include "DRW_engine.hh"
#include "DRW_render.hh" /* For DRW_shgroup_get_instance_count() */

#include "BLI_listbase.h"
#include "BLI_mempool.h"

#include "MEM_guardedalloc.h"

struct DRWInstanceData {
  DRWInstanceData *next;
  bool used;        /* If this data is used or not. */
  size_t data_size; /* Size of one instance data. */
  BLI_mempool *mempool;
};

struct DRWInstanceDataList {
  DRWInstanceDataList *next, *prev;
  /* Linked lists for all possible data pool size */
  DRWInstanceData *idata_head[MAX_INSTANCE_DATA_SIZE];
  DRWInstanceData *idata_tail[MAX_INSTANCE_DATA_SIZE];
};

struct DRWTempBufferHandle {
  blender::gpu::VertBuf *buf;
  /** Format pointer for reuse. */
  GPUVertFormat *format;
  /** Touched vertex length for resize. */
  int *vert_len;
};

struct DRWTempInstancingHandle {
  /** Copy of geom but with the per-instance attributes. */
  blender::gpu::Batch *batch;
  /** Batch containing instancing attributes. */
  blender::gpu::Batch *instancer;
  /** Call-buffer to be used instead of instancer. */
  blender::gpu::VertBuf *buf;
  /** Original non-instanced batch pointer. */
  blender::gpu::Batch *geom;
};

static ListBase g_idatalists = {nullptr, nullptr};

/* -------------------------------------------------------------------- */
/** \name Instance Data (DRWInstanceData)
 * \{ */

static DRWInstanceData *drw_instance_data_create(DRWInstanceDataList *idatalist, uint attr_size)
{
  DRWInstanceData *idata = static_cast<DRWInstanceData *>(
      MEM_callocN(sizeof(DRWInstanceData), "DRWInstanceData"));
  idata->next = nullptr;
  idata->used = true;
  idata->data_size = attr_size;
  idata->mempool = BLI_mempool_create(sizeof(float) * idata->data_size, 0, 16, 0);

  BLI_assert(attr_size > 0);

  /* Push to linked list. */
  if (idatalist->idata_head[attr_size - 1] == nullptr) {
    idatalist->idata_head[attr_size - 1] = idata;
  }
  else {
    idatalist->idata_tail[attr_size - 1]->next = idata;
  }
  idatalist->idata_tail[attr_size - 1] = idata;

  return idata;
}

static void DRW_instance_data_free(DRWInstanceData *idata)
{
  BLI_mempool_destroy(idata->mempool);
}

void *DRW_instance_data_next(DRWInstanceData *idata)
{
  return BLI_mempool_alloc(idata->mempool);
}

DRWInstanceData *DRW_instance_data_request(DRWInstanceDataList *idatalist, uint attr_size)
{
  BLI_assert(attr_size > 0 && attr_size <= MAX_INSTANCE_DATA_SIZE);

  DRWInstanceData *idata = idatalist->idata_head[attr_size - 1];

  /* Search for an unused data chunk. */
  for (; idata; idata = idata->next) {
    if (idata->used == false) {
      idata->used = true;
      return idata;
    }
  }

  return drw_instance_data_create(idatalist, attr_size);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Instance Data List (DRWInstanceDataList)
 * \{ */

DRWInstanceDataList *DRW_instance_data_list_create()
{
  DRWInstanceDataList *idatalist = static_cast<DRWInstanceDataList *>(
      MEM_callocN(sizeof(DRWInstanceDataList), "DRWInstanceDataList"));

  BLI_addtail(&g_idatalists, idatalist);

  return idatalist;
}

void DRW_instance_data_list_free(DRWInstanceDataList *idatalist)
{
  DRWInstanceData *idata, *next_idata;

  for (int i = 0; i < MAX_INSTANCE_DATA_SIZE; i++) {
    for (idata = idatalist->idata_head[i]; idata; idata = next_idata) {
      next_idata = idata->next;
      DRW_instance_data_free(idata);
      MEM_freeN(idata);
    }
    idatalist->idata_head[i] = nullptr;
    idatalist->idata_tail[i] = nullptr;
  }

  BLI_remlink(&g_idatalists, idatalist);

  MEM_freeN(idatalist);
}

void DRW_instance_data_list_reset(DRWInstanceDataList *idatalist)
{
  DRWInstanceData *idata;

  for (int i = 0; i < MAX_INSTANCE_DATA_SIZE; i++) {
    for (idata = idatalist->idata_head[i]; idata; idata = idata->next) {
      idata->used = false;
    }
  }
}

void DRW_instance_data_list_free_unused(DRWInstanceDataList *idatalist)
{
  DRWInstanceData *idata, *next_idata;

  /* Remove unused data blocks and sanitize each list. */
  for (int i = 0; i < MAX_INSTANCE_DATA_SIZE; i++) {
    idatalist->idata_tail[i] = nullptr;
    for (idata = idatalist->idata_head[i]; idata; idata = next_idata) {
      next_idata = idata->next;
      if (idata->used == false) {
        if (idatalist->idata_head[i] == idata) {
          idatalist->idata_head[i] = next_idata;
        }
        else {
          /* idatalist->idata_tail[i] is guaranteed not to be null in this case. */
          idatalist->idata_tail[i]->next = next_idata;
        }
        DRW_instance_data_free(idata);
        MEM_freeN(idata);
      }
      else {
        if (idatalist->idata_tail[i] != nullptr) {
          idatalist->idata_tail[i]->next = idata;
        }
        idatalist->idata_tail[i] = idata;
      }
    }
  }
}

void DRW_instance_data_list_resize(DRWInstanceDataList *idatalist)
{
  DRWInstanceData *idata;

  for (int i = 0; i < MAX_INSTANCE_DATA_SIZE; i++) {
    for (idata = idatalist->idata_head[i]; idata; idata = idata->next) {
      BLI_mempool_clear_ex(idata->mempool, BLI_mempool_len(idata->mempool));
    }
  }
}

/** \} */