/* SPDX-FileCopyrightText: 2016 by Mike Erwin. All rights reserved.
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

/** \file
 * \ingroup gpu
 *
 * GPU geometric primitives
 */

#pragma once

#include "BLI_assert.h"
#include "BLI_sys_types.h"

enum GPUPrimType {
  GPU_PRIM_POINTS,
  GPU_PRIM_LINES,
  GPU_PRIM_TRIS,
  GPU_PRIM_LINE_STRIP,
  GPU_PRIM_LINE_LOOP, /* GL has this, Vulkan and Metal do not */
  GPU_PRIM_TRI_STRIP,
  GPU_PRIM_TRI_FAN, /* Metal API does not support this. */

  /* Metal API does not support ADJ primitive types but
   * handled via the geometry-shader-alternative path. */
  GPU_PRIM_LINES_ADJ,
  GPU_PRIM_TRIS_ADJ,
  GPU_PRIM_LINE_STRIP_ADJ,

  GPU_PRIM_NONE,
};

/* what types of primitives does each shader expect? */
enum GPUPimClass {
  GPU_PRIM_CLASS_NONE = 0,
  GPU_PRIM_CLASS_POINT = (1 << 0),
  GPU_PRIM_CLASS_LINE = (1 << 1),
  GPU_PRIM_CLASS_SURFACE = (1 << 2),
  GPU_PRIM_CLASS_ANY = GPU_PRIM_CLASS_POINT | GPU_PRIM_CLASS_LINE | GPU_PRIM_CLASS_SURFACE,
};

inline int gpu_get_prim_count_from_type(uint vertex_len, GPUPrimType prim_type)
{
  /* does vertex_len make sense for this primitive type? */
  if (vertex_len == 0) {
    return 0;
  }

  switch (prim_type) {
    case GPU_PRIM_POINTS:
      return vertex_len;

    case GPU_PRIM_LINES:
      BLI_assert(vertex_len % 2 == 0);
      return vertex_len / 2;

    case GPU_PRIM_LINE_STRIP:
      return vertex_len - 1;

    case GPU_PRIM_LINE_LOOP:
      return vertex_len;

    case GPU_PRIM_LINES_ADJ:
      BLI_assert(vertex_len % 4 == 0);
      return vertex_len / 4;

    case GPU_PRIM_LINE_STRIP_ADJ:
      return vertex_len - 2;

    case GPU_PRIM_TRIS:
      BLI_assert(vertex_len % 3 == 0);
      return vertex_len / 3;

    case GPU_PRIM_TRI_STRIP:
      BLI_assert(vertex_len >= 3);
      return vertex_len - 2;

    case GPU_PRIM_TRI_FAN:
      BLI_assert(vertex_len >= 3);
      return vertex_len - 2;

    case GPU_PRIM_TRIS_ADJ:
      BLI_assert(vertex_len % 6 == 0);
      return vertex_len / 6;

    default:
      BLI_assert_unreachable();
      return 0;
  }
}

inline bool is_restart_compatible(GPUPrimType type)
{
  switch (type) {
    case GPU_PRIM_POINTS:
    case GPU_PRIM_LINES:
    case GPU_PRIM_TRIS:
    case GPU_PRIM_LINES_ADJ:
    case GPU_PRIM_TRIS_ADJ:
    case GPU_PRIM_NONE:
    default: {
      return false;
    }
    case GPU_PRIM_LINE_STRIP:
    case GPU_PRIM_LINE_LOOP:
    case GPU_PRIM_TRI_STRIP:
    case GPU_PRIM_TRI_FAN:
    case GPU_PRIM_LINE_STRIP_ADJ: {
      return true;
    }
  }
  return false;
}

/**
 * TODO: Improve error checking by validating that the shader is suited for this primitive type.
 * GPUPrimClass GPU_primtype_class(GPUPrimType);
 * bool GPU_primtype_belongs_to_class(GPUPrimType, GPUPrimClass);
 */