/*
 * This program 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; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * The Original Code is Copyright (C) 2016 by Mike Erwin.
 * All rights reserved.
 */

/** \file
 * \ingroup gpu
 *
 * GPU geometry batch
 * Contains VAOs + VBOs + Shader representing a drawable entity.
 */

#include "MEM_guardedalloc.h"

#include "GPU_batch.h"
#include "GPU_batch_presets.h"
#include "GPU_extensions.h"
#include "GPU_matrix.h"
#include "GPU_platform.h"
#include "GPU_shader.h"

#include "gpu_batch_private.hh"
#include "gpu_context_private.hh"
#include "gpu_primitive_private.h"
#include "gpu_shader_private.h"
#include "gpu_vertex_format_private.h"

#include <limits.h>
#include <stdlib.h>
#include <string.h>

static GLuint g_default_attr_vbo = 0;

static void gpu_batch_bind(GPUBatch *batch);
static void batch_update_program_bindings(GPUBatch *batch, uint i_first);

void GPU_batch_vao_cache_clear(GPUBatch *batch)
{
  if (batch->context == NULL) {
    return;
  }
  if (batch->is_dynamic_vao_count) {
    for (int i = 0; i < batch->dynamic_vaos.count; i++) {
      if (batch->dynamic_vaos.vao_ids[i]) {
        GPU_vao_free(batch->dynamic_vaos.vao_ids[i], batch->context);
      }
      if (batch->dynamic_vaos.interfaces[i]) {
        GPU_shaderinterface_remove_batch_ref(
            (GPUShaderInterface *)batch->dynamic_vaos.interfaces[i], batch);
      }
    }
    MEM_freeN((void *)batch->dynamic_vaos.interfaces);
    MEM_freeN(batch->dynamic_vaos.vao_ids);
  }
  else {
    for (int i = 0; i < GPU_BATCH_VAO_STATIC_LEN; i++) {
      if (batch->static_vaos.vao_ids[i]) {
        GPU_vao_free(batch->static_vaos.vao_ids[i], batch->context);
      }
      if (batch->static_vaos.interfaces[i]) {
        GPU_shaderinterface_remove_batch_ref(
            (GPUShaderInterface *)batch->static_vaos.interfaces[i], batch);
      }
    }
  }
  batch->is_dynamic_vao_count = false;
  for (int i = 0; i < GPU_BATCH_VAO_STATIC_LEN; i++) {
    batch->static_vaos.vao_ids[i] = 0;
    batch->static_vaos.interfaces[i] = NULL;
  }
  gpu_context_remove_batch(batch->context, batch);
  batch->context = NULL;
}

GPUBatch *GPU_batch_calloc(uint count)
{
  return (GPUBatch *)MEM_callocN(sizeof(GPUBatch) * count, "GPUBatch");
}

GPUBatch *GPU_batch_create_ex(GPUPrimType prim_type,
                              GPUVertBuf *verts,
                              GPUIndexBuf *elem,
                              uint owns_flag)
{
  GPUBatch *batch = GPU_batch_calloc(1);
  GPU_batch_init_ex(batch, prim_type, verts, elem, owns_flag);
  return batch;
}

void GPU_batch_init_ex(
    GPUBatch *batch, GPUPrimType prim_type, GPUVertBuf *verts, GPUIndexBuf *elem, uint owns_flag)
{
#if TRUST_NO_ONE
  assert(verts != NULL);
#endif

  batch->verts[0] = verts;
  for (int v = 1; v < GPU_BATCH_VBO_MAX_LEN; v++) {
    batch->verts[v] = NULL;
  }
  for (int v = 0; v < GPU_BATCH_INST_VBO_MAX_LEN; v++) {
    batch->inst[v] = NULL;
  }
  batch->elem = elem;
  batch->prim_type = prim_type;
  batch->phase = GPU_BATCH_READY_TO_DRAW;
  batch->is_dynamic_vao_count = false;
  batch->owns_flag = owns_flag;
}

/* This will share the VBOs with the new batch. */
void GPU_batch_copy(GPUBatch *batch_dst, GPUBatch *batch_src)
{
  GPU_batch_init_ex(batch_dst, GPU_PRIM_POINTS, batch_src->verts[0], batch_src->elem, 0);

  batch_dst->prim_type = batch_src->prim_type;
  for (int v = 1; v < GPU_BATCH_VBO_MAX_LEN; v++) {
    batch_dst->verts[v] = batch_src->verts[v];
  }
}

void GPU_batch_clear(GPUBatch *batch)
{
  if (batch->owns_flag & GPU_BATCH_OWNS_INDEX) {
    GPU_indexbuf_discard(batch->elem);
  }
  if (batch->owns_flag & GPU_BATCH_OWNS_INSTANCES) {
    GPU_vertbuf_discard(batch->inst[0]);
    GPU_VERTBUF_DISCARD_SAFE(batch->inst[1]);
  }
  if ((batch->owns_flag & ~GPU_BATCH_OWNS_INDEX) != 0) {
    for (int v = 0; v < GPU_BATCH_VBO_MAX_LEN; v++) {
      if (batch->verts[v] == NULL) {
        break;
      }
      if (batch->owns_flag & (1 << v)) {
        GPU_vertbuf_discard(batch->verts[v]);
      }
    }
  }
  GPU_batch_vao_cache_clear(batch);
  batch->phase = GPU_BATCH_UNUSED;
}

void GPU_batch_discard(GPUBatch *batch)
{
  GPU_batch_clear(batch);
  MEM_freeN(batch);
}

void GPU_batch_instbuf_set(GPUBatch *batch, GPUVertBuf *inst, bool own_vbo)
{
#if TRUST_NO_ONE
  assert(inst != NULL);
#endif
  /* redo the bindings */
  GPU_batch_vao_cache_clear(batch);

  if (batch->inst[0] != NULL && (batch->owns_flag & GPU_BATCH_OWNS_INSTANCES)) {
    GPU_vertbuf_discard(batch->inst[0]);
    GPU_VERTBUF_DISCARD_SAFE(batch->inst[1]);
  }
  batch->inst[0] = inst;

  if (own_vbo) {
    batch->owns_flag |= GPU_BATCH_OWNS_INSTANCES;
  }
  else {
    batch->owns_flag &= ~GPU_BATCH_OWNS_INSTANCES;
  }
}

void GPU_batch_elembuf_set(GPUBatch *batch, GPUIndexBuf *elem, bool own_ibo)
{
  BLI_assert(elem != NULL);
  /* redo the bindings */
  GPU_batch_vao_cache_clear(batch);

  if (batch->elem != NULL && (batch->owns_flag & GPU_BATCH_OWNS_INDEX)) {
    GPU_indexbuf_discard(batch->elem);
  }
  batch->elem = elem;

  if (own_ibo) {
    batch->owns_flag |= GPU_BATCH_OWNS_INDEX;
  }
  else {
    batch->owns_flag &= ~GPU_BATCH_OWNS_INDEX;
  }
}

/* A bit of a quick hack. Should be streamlined as the vbos handling */
int GPU_batch_instbuf_add_ex(GPUBatch *batch, GPUVertBuf *insts, bool own_vbo)
{
  /* redo the bindings */
  GPU_batch_vao_cache_clear(batch);

  for (uint v = 0; v < GPU_BATCH_INST_VBO_MAX_LEN; v++) {
    if (batch->inst[v] == NULL) {
#if TRUST_NO_ONE
      /* for now all VertexBuffers must have same vertex_len */
      if (batch->inst[0] != NULL) {
        /* Allow for different size of vertex buf (will choose the smallest number of verts). */
        // assert(insts->vertex_len == batch->inst[0]->vertex_len);
        assert(own_vbo == ((batch->owns_flag & GPU_BATCH_OWNS_INSTANCES) != 0));
      }
#endif
      batch->inst[v] = insts;
      if (own_vbo) {
        batch->owns_flag |= GPU_BATCH_OWNS_INSTANCES;
      }
      return v;
    }
  }

  /* we only make it this far if there is no room for another GPUVertBuf */
#if TRUST_NO_ONE
  assert(false);
#endif
  return -1;
}

/* Returns the index of verts in the batch. */
int GPU_batch_vertbuf_add_ex(GPUBatch *batch, GPUVertBuf *verts, bool own_vbo)
{
  /* redo the bindings */
  GPU_batch_vao_cache_clear(batch);

  for (uint v = 0; v < GPU_BATCH_VBO_MAX_LEN; v++) {
    if (batch->verts[v] == NULL) {
#if TRUST_NO_ONE
      /* for now all VertexBuffers must have same vertex_len */
      if (batch->verts[0] != NULL) {
        assert(verts->vertex_len == batch->verts[0]->vertex_len);
      }
#endif
      batch->verts[v] = verts;
      /* TODO: mark dirty so we can keep attribute bindings up-to-date */
      if (own_vbo) {
        batch->owns_flag |= (1 << v);
      }
      return v;
    }
  }

  /* we only make it this far if there is no room for another GPUVertBuf */
#if TRUST_NO_ONE
  assert(false);
#endif
  return -1;
}

static GLuint batch_vao_get(GPUBatch *batch)
{
  /* Search through cache */
  if (batch->is_dynamic_vao_count) {
    for (int i = 0; i < batch->dynamic_vaos.count; i++) {
      if (batch->dynamic_vaos.interfaces[i] == batch->interface) {
        return batch->dynamic_vaos.vao_ids[i];
      }
    }
  }
  else {
    for (int i = 0; i < GPU_BATCH_VAO_STATIC_LEN; i++) {
      if (batch->static_vaos.interfaces[i] == batch->interface) {
        return batch->static_vaos.vao_ids[i];
      }
    }
  }

  /* Set context of this batch.
   * It will be bound to it until GPU_batch_vao_cache_clear is called.
   * Until then it can only be drawn with this context. */
  if (batch->context == NULL) {
    batch->context = GPU_context_active_get();
    gpu_context_add_batch(batch->context, batch);
  }
#if TRUST_NO_ONE
  else {
    /* Make sure you are not trying to draw this batch in another context. */
    assert(batch->context == GPU_context_active_get());
  }
#endif

  /* Cache miss, time to add a new entry! */
  GLuint new_vao = 0;
  if (!batch->is_dynamic_vao_count) {
    int i; /* find first unused slot */
    for (i = 0; i < GPU_BATCH_VAO_STATIC_LEN; i++) {
      if (batch->static_vaos.vao_ids[i] == 0) {
        break;
      }
    }

    if (i < GPU_BATCH_VAO_STATIC_LEN) {
      batch->static_vaos.interfaces[i] = batch->interface;
      batch->static_vaos.vao_ids[i] = new_vao = GPU_vao_alloc();
    }
    else {
      /* Not enough place switch to dynamic. */
      batch->is_dynamic_vao_count = true;
      /* Erase previous entries, they will be added back if drawn again. */
      for (int j = 0; j < GPU_BATCH_VAO_STATIC_LEN; j++) {
        GPU_shaderinterface_remove_batch_ref(
            (GPUShaderInterface *)batch->static_vaos.interfaces[j], batch);
        GPU_vao_free(batch->static_vaos.vao_ids[j], batch->context);
      }
      /* Init dynamic arrays and let the branch below set the values. */
      batch->dynamic_vaos.count = GPU_BATCH_VAO_DYN_ALLOC_COUNT;
      batch->dynamic_vaos.interfaces = (const GPUShaderInterface **)MEM_callocN(
          batch->dynamic_vaos.count * sizeof(GPUShaderInterface *), "dyn vaos interfaces");
      batch->dynamic_vaos.vao_ids = (GLuint *)MEM_callocN(
          batch->dynamic_vaos.count * sizeof(GLuint), "dyn vaos ids");
    }
  }

  if (batch->is_dynamic_vao_count) {
    int i; /* find first unused slot */
    for (i = 0; i < batch->dynamic_vaos.count; i++) {
      if (batch->dynamic_vaos.vao_ids[i] == 0) {
        break;
      }
    }

    if (i == batch->dynamic_vaos.count) {
      /* Not enough place, realloc the array. */
      i = batch->dynamic_vaos.count;
      batch->dynamic_vaos.count += GPU_BATCH_VAO_DYN_ALLOC_COUNT;
      batch->dynamic_vaos.interfaces = (const GPUShaderInterface **)MEM_recallocN(
          (void *)batch->dynamic_vaos.interfaces,
          sizeof(GPUShaderInterface *) * batch->dynamic_vaos.count);
      batch->dynamic_vaos.vao_ids = (GLuint *)MEM_recallocN(
          batch->dynamic_vaos.vao_ids, sizeof(GLuint) * batch->dynamic_vaos.count);
    }
    batch->dynamic_vaos.interfaces[i] = batch->interface;
    batch->dynamic_vaos.vao_ids[i] = new_vao = GPU_vao_alloc();
  }

  GPU_shaderinterface_add_batch_ref((GPUShaderInterface *)batch->interface, batch);

#if TRUST_NO_ONE
  assert(new_vao != 0);
#endif

  /* We just got a fresh VAO we need to initialize it. */
  glBindVertexArray(new_vao);
  batch_update_program_bindings(batch, 0);
  glBindVertexArray(0);

  return new_vao;
}

void GPU_batch_set_shader(GPUBatch *batch, GPUShader *shader)
{
  batch->interface = shader->interface;
  batch->shader = shader;
  batch->vao_id = batch_vao_get(batch);
  GPU_shader_bind(batch->shader);
  GPU_matrix_bind(batch->shader->interface);
  GPU_shader_set_srgb_uniform(batch->shader->interface);
  gpu_batch_bind(batch);
}

void gpu_batch_remove_interface_ref(GPUBatch *batch, const GPUShaderInterface *interface)
{
  if (batch->is_dynamic_vao_count) {
    for (int i = 0; i < batch->dynamic_vaos.count; i++) {
      if (batch->dynamic_vaos.interfaces[i] == interface) {
        GPU_vao_free(batch->dynamic_vaos.vao_ids[i], batch->context);
        batch->dynamic_vaos.vao_ids[i] = 0;
        batch->dynamic_vaos.interfaces[i] = NULL;
        break; /* cannot have duplicates */
      }
    }
  }
  else {
    int i;
    for (i = 0; i < GPU_BATCH_VAO_STATIC_LEN; i++) {
      if (batch->static_vaos.interfaces[i] == interface) {
        GPU_vao_free(batch->static_vaos.vao_ids[i], batch->context);
        batch->static_vaos.vao_ids[i] = 0;
        batch->static_vaos.interfaces[i] = NULL;
        break; /* cannot have duplicates */
      }
    }
  }
}

static void create_bindings(GPUVertBuf *verts,
                            const GPUShaderInterface *interface,
                            uint16_t *attr_mask,
                            uint v_first,
                            const bool use_instancing)
{
  const GPUVertFormat *format = &verts->format;

  const uint attr_len = format->attr_len;
  uint stride = format->stride;
  uint offset = 0;

  GPU_vertbuf_use(verts);

  for (uint a_idx = 0; a_idx < attr_len; a_idx++) {
    const GPUVertAttr *a = &format->attrs[a_idx];

    if (format->deinterleaved) {
      offset += ((a_idx == 0) ? 0 : format->attrs[a_idx - 1].sz) * verts->vertex_len;
      stride = a->sz;
    }
    else {
      offset = a->offset;
    }

    const GLvoid *pointer = (const GLubyte *)0 + offset + v_first * stride;
    const GLenum type = convert_comp_type_to_gl(static_cast<GPUVertCompType>(a->comp_type));

    for (uint n_idx = 0; n_idx < a->name_len; n_idx++) {
      const char *name = GPU_vertformat_attr_name_get(format, a, n_idx);
      const GPUShaderInput *input = GPU_shaderinterface_attr(interface, name);

      if (input == NULL) {
        continue;
      }

      *attr_mask &= ~(1 << input->location);

      if (a->comp_len == 16 || a->comp_len == 12 || a->comp_len == 8) {
        BLI_assert(a->fetch_mode == GPU_FETCH_FLOAT);
        BLI_assert(a->comp_type == GPU_COMP_F32);
        for (int i = 0; i < a->comp_len / 4; i++) {
          glEnableVertexAttribArray(input->location + i);
          glVertexAttribDivisor(input->location + i, (use_instancing) ? 1 : 0);
          glVertexAttribPointer(
              input->location + i, 4, type, GL_FALSE, stride, (const GLubyte *)pointer + i * 16);
        }
      }
      else {
        glEnableVertexAttribArray(input->location);
        glVertexAttribDivisor(input->location, (use_instancing) ? 1 : 0);

        switch (a->fetch_mode) {
          case GPU_FETCH_FLOAT:
          case GPU_FETCH_INT_TO_FLOAT:
            glVertexAttribPointer(input->location, a->comp_len, type, GL_FALSE, stride, pointer);
            break;
          case GPU_FETCH_INT_TO_FLOAT_UNIT:
            glVertexAttribPointer(input->location, a->comp_len, type, GL_TRUE, stride, pointer);
            break;
          case GPU_FETCH_INT:
            glVertexAttribIPointer(input->location, a->comp_len, type, stride, pointer);
            break;
        }
      }
    }
  }
}

static void batch_update_program_bindings(GPUBatch *batch, uint i_first)
{
  uint16_t attr_mask = batch->interface->enabled_attr_mask;

  /* Reverse order so first VBO'S have more prevalence (in term of attribute override). */
  for (int v = GPU_BATCH_VBO_MAX_LEN - 1; v > -1; v--) {
    if (batch->verts[v] != NULL) {
      create_bindings(batch->verts[v], batch->interface, &attr_mask, 0, false);
    }
  }

  for (int v = GPU_BATCH_INST_VBO_MAX_LEN - 1; v > -1; v--) {
    if (batch->inst[v]) {
      create_bindings(batch->inst[v], batch->interface, &attr_mask, i_first, true);
    }
  }

  if (attr_mask != 0 && GLEW_ARB_vertex_attrib_binding) {
    for (uint16_t mask = 1, a = 0; a < 16; a++, mask <<= 1) {
      if (attr_mask & mask) {
        /* This replaces glVertexAttrib4f(a, 0.0f, 0.0f, 0.0f, 1.0f); with a more modern style.
         * Fix issues for some drivers (see T75069). */
        glBindVertexBuffer(a, g_default_attr_vbo, (intptr_t)0, (intptr_t)0);

        glEnableVertexAttribArray(a);
        glVertexAttribFormat(a, 4, GL_FLOAT, GL_FALSE, 0);
        glVertexAttribBinding(a, a);
      }
    }
  }

  if (batch->elem) {
    GPU_indexbuf_use(batch->elem);
  }
}

/* -------------------------------------------------------------------- */
/** \name Uniform setters
 * \{ */

#define GET_UNIFORM \
  const GPUShaderInput *uniform = GPU_shaderinterface_uniform(batch->interface, name); \
  BLI_assert(uniform);

void GPU_batch_uniform_1i(GPUBatch *batch, const char *name, int value)
{
  GET_UNIFORM
  GPU_shader_uniform_int(batch->shader, uniform->location, value);
}

void GPU_batch_uniform_1b(GPUBatch *batch, const char *name, bool value)
{
  GPU_batch_uniform_1i(batch, name, value ? GL_TRUE : GL_FALSE);
}

void GPU_batch_uniform_2f(GPUBatch *batch, const char *name, float x, float y)
{
  const float data[2] = {x, y};
  GPU_batch_uniform_2fv(batch, name, data);
}

void GPU_batch_uniform_3f(GPUBatch *batch, const char *name, float x, float y, float z)
{
  const float data[3] = {x, y, z};
  GPU_batch_uniform_3fv(batch, name, data);
}

void GPU_batch_uniform_4f(GPUBatch *batch, const char *name, float x, float y, float z, float w)
{
  const float data[4] = {x, y, z, w};
  GPU_batch_uniform_4fv(batch, name, data);
}

void GPU_batch_uniform_1f(GPUBatch *batch, const char *name, float x)
{
  GET_UNIFORM
  GPU_shader_uniform_float(batch->shader, uniform->location, x);
}

void GPU_batch_uniform_2fv(GPUBatch *batch, const char *name, const float data[2])
{
  GET_UNIFORM
  GPU_shader_uniform_vector(batch->shader, uniform->location, 2, 1, data);
}

void GPU_batch_uniform_3fv(GPUBatch *batch, const char *name, const float data[3])
{
  GET_UNIFORM
  GPU_shader_uniform_vector(batch->shader, uniform->location, 3, 1, data);
}

void GPU_batch_uniform_4fv(GPUBatch *batch, const char *name, const float data[4])
{
  GET_UNIFORM
  GPU_shader_uniform_vector(batch->shader, uniform->location, 4, 1, data);
}

void GPU_batch_uniform_2fv_array(GPUBatch *batch,
                                 const char *name,
                                 const int len,
                                 const float *data)
{
  GET_UNIFORM
  GPU_shader_uniform_vector(batch->shader, uniform->location, 2, len, data);
}

void GPU_batch_uniform_4fv_array(GPUBatch *batch,
                                 const char *name,
                                 const int len,
                                 const float *data)
{
  GET_UNIFORM
  GPU_shader_uniform_vector(batch->shader, uniform->location, 4, len, data);
}

void GPU_batch_uniform_mat4(GPUBatch *batch, const char *name, const float data[4][4])
{
  GET_UNIFORM
  GPU_shader_uniform_vector(batch->shader, uniform->location, 16, 1, (const float *)data);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Drawing / Drawcall functions
 * \{ */

static void *elem_offset(const GPUIndexBuf *el, int v_first)
{
#if GPU_TRACK_INDEX_RANGE
  if (el->index_type == GPU_INDEX_U16) {
    return (GLushort *)0 + v_first + el->index_start;
  }
#endif
  return (GLuint *)0 + v_first + el->index_start;
}

/* Use when drawing with GPU_batch_draw_advanced */
static void gpu_batch_bind(GPUBatch *batch)
{
  glBindVertexArray(batch->vao_id);

#if GPU_TRACK_INDEX_RANGE
  /* Can be removed if GL 4.3 is required. */
  if (!GLEW_ARB_ES3_compatibility && batch->elem != NULL) {
    GLuint restart_index = (batch->elem->index_type == GPU_INDEX_U16) ? (GLuint)0xFFFF :
                                                                        (GLuint)0xFFFFFFFF;
    glPrimitiveRestartIndex(restart_index);
  }
#endif
}

void GPU_batch_draw(GPUBatch *batch)
{
  GPU_shader_bind(batch->shader);
  GPU_batch_draw_advanced(batch, 0, 0, 0, 0);
  GPU_shader_unbind();
}

void GPU_batch_draw_range(GPUBatch *batch, int v_first, int v_count)
{
  GPU_shader_bind(batch->shader);
  GPU_batch_draw_advanced(batch, v_first, v_count, 0, 0);
  GPU_shader_unbind();
}

/* Draw multiple instance of a batch without having any instance attributes. */
void GPU_batch_draw_instanced(GPUBatch *batch, int i_count)
{
  BLI_assert(batch->inst[0] == NULL);

  GPU_shader_bind(batch->shader);
  GPU_batch_draw_advanced(batch, 0, 0, 0, i_count);
  GPU_shader_unbind();
}

#if GPU_TRACK_INDEX_RANGE
#  define BASE_INDEX(el) ((el)->base_index)
#  define INDEX_TYPE(el) ((el)->gl_index_type)
#else
#  define BASE_INDEX(el) 0
#  define INDEX_TYPE(el) GL_UNSIGNED_INT
#endif

void GPU_batch_draw_advanced(GPUBatch *batch, int v_first, int v_count, int i_first, int i_count)
{
  BLI_assert(GPU_context_active_get()->shader != NULL);
  /* TODO could assert that VAO is bound. */

  if (v_count == 0) {
    v_count = (batch->elem) ? batch->elem->index_len : batch->verts[0]->vertex_len;
  }
  if (i_count == 0) {
    i_count = (batch->inst[0]) ? batch->inst[0]->vertex_len : 1;
    /* Meh. This is to be able to use different numbers of verts in instance vbos. */
    if (batch->inst[1] && i_count > batch->inst[1]->vertex_len) {
      i_count = batch->inst[1]->vertex_len;
    }
  }

  if (v_count == 0 || i_count == 0) {
    /* Nothing to draw. */
    return;
  }

  /* Verify there is enough data do draw. */
  /* TODO(fclem) Nice to have but this is invalid when using procedural draw-calls.
   * The right assert would be to check if there is an enabled attribute from each VBO
   * and check their length. */
  // BLI_assert(i_first + i_count <= (batch->inst ? batch->inst->vertex_len : INT_MAX));
  // BLI_assert(v_first + v_count <=
  //            (batch->elem ? batch->elem->index_len : batch->verts[0]->vertex_len));

#ifdef __APPLE__
  GLuint vao = 0;
#endif

  if (!GPU_arb_base_instance_is_supported()) {
    if (i_first > 0) {
#ifdef __APPLE__
      /**
       * There seems to be a nasty bug when drawing using the same VAO reconfiguring. (see T71147)
       * We just use a throwaway VAO for that. Note that this is likely to degrade performance.
       **/
      glGenVertexArrays(1, &vao);
      glBindVertexArray(vao);
#else
      /* If using offset drawing with instancing, we must
       * use the default VAO and redo bindings. */
      glBindVertexArray(GPU_vao_default());
#endif
      batch_update_program_bindings(batch, i_first);
    }
    else {
      /* Previous call could have bind the default vao
       * see above. */
      glBindVertexArray(batch->vao_id);
    }
  }

  GLenum gl_prim_type = convert_prim_type_to_gl(batch->prim_type);

  if (batch->elem) {
    const GPUIndexBuf *el = batch->elem;
    GLenum index_type = INDEX_TYPE(el);
    GLint base_index = BASE_INDEX(el);
    void *v_first_ofs = elem_offset(el, v_first);

    if (GPU_arb_base_instance_is_supported()) {
      glDrawElementsInstancedBaseVertexBaseInstance(
          gl_prim_type, v_count, index_type, v_first_ofs, i_count, base_index, i_first);
    }
    else {
      glDrawElementsInstancedBaseVertex(
          gl_prim_type, v_count, index_type, v_first_ofs, i_count, base_index);
    }
  }
  else {
#ifdef __APPLE__
    glDisable(GL_PRIMITIVE_RESTART);
#endif
    if (GPU_arb_base_instance_is_supported()) {
      glDrawArraysInstancedBaseInstance(gl_prim_type, v_first, v_count, i_count, i_first);
    }
    else {
      glDrawArraysInstanced(gl_prim_type, v_first, v_count, i_count);
    }
#ifdef __APPLE__
    glEnable(GL_PRIMITIVE_RESTART);
#endif
  }

#ifdef __APPLE__
  if (vao != 0) {
    glDeleteVertexArrays(1, &vao);
  }
#endif
}

/* just draw some vertices and let shader place them where we want. */
void GPU_draw_primitive(GPUPrimType prim_type, int v_count)
{
  /* we cannot draw without vao ... annoying ... */
  glBindVertexArray(GPU_vao_default());

  GLenum type = convert_prim_type_to_gl(prim_type);
  glDrawArrays(type, 0, v_count);

  /* Performance hog if you are drawing with the same vao multiple time.
   * Only activate for debugging.*/
  // glBindVertexArray(0);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Utilities
 * \{ */

void GPU_batch_program_set_builtin_with_config(GPUBatch *batch,
                                               eGPUBuiltinShader shader_id,
                                               eGPUShaderConfig sh_cfg)
{
  GPUShader *shader = GPU_shader_get_builtin_shader_with_config(shader_id, sh_cfg);
  GPU_batch_set_shader(batch, shader);
}

void GPU_batch_program_set_builtin(GPUBatch *batch, eGPUBuiltinShader shader_id)
{
  GPU_batch_program_set_builtin_with_config(batch, shader_id, GPU_SHADER_CFG_DEFAULT);
}

/* Bind program bound to IMM to the batch.
 * XXX Use this with much care. Drawing with the GPUBatch API is not compatible with IMM.
 * DO NOT DRAW WITH THE BATCH BEFORE CALLING immUnbindProgram. */
void GPU_batch_program_set_imm_shader(GPUBatch *batch)
{
  GPU_batch_set_shader(batch, immGetShader());
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Init/Exit
 * \{ */

void gpu_batch_init(void)
{
  if (g_default_attr_vbo == 0) {
    g_default_attr_vbo = GPU_buf_alloc();

    float default_attrib_data[4] = {0.0f, 0.0f, 0.0f, 1.0f};
    glBindBuffer(GL_ARRAY_BUFFER, g_default_attr_vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(float[4]), default_attrib_data, GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
  }

  gpu_batch_presets_init();
}

void gpu_batch_exit(void)
{
  GPU_buf_free(g_default_attr_vbo);
  g_default_attr_vbo = 0;

  gpu_batch_presets_exit();
}

/** \} */