// Copyright 2021, 2022 Benjamin Barenblat
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.

#ifndef GLPLANET_SRC_MESH_H_
#define GLPLANET_SRC_MESH_H_

#include <stdint.h>

#include <ostream>
#include <string>
#include <vector>

#include "third_party/abseil/absl/base/attributes.h"

namespace glplanet {

// A UV-mapped sphere.
struct UvSphere {
  // A point on the sphere--a vector of 5-tuples (x, y, z, u, v).
  //
  //   - (x, y, z) are the Cartesian coordinates of each vertex in right-handed
  //     model space--that is, with x forward, y to the right, and z upward.
  //
  //   - (u, v) are texture coordinates, with (0, 0) corresponding to the north
  //     pole at 180 degrees of longitude. (This matches the way textures are
  //     loaded into memory from an image in plate carree projection.) The u
  //     coordinates are not in the range [0, 1], so you will need to set your
  //     texture to GL_REPEAT in the s direction.
  struct Coordinates {
    float x ABSL_ATTRIBUTE_PACKED;
    float y ABSL_ATTRIBUTE_PACKED;
    float z ABSL_ATTRIBUTE_PACKED;

    float u ABSL_ATTRIBUTE_PACKED;
    float v ABSL_ATTRIBUTE_PACKED;

    std::string DebugString() const noexcept;
  };

  // Creates a UV-mapped unit sphere. sectors_per_turn specifies the number of
  // latitude steps per 360-degree turn; slices specifies the number of vertical
  // slices of the sphere. These must both be at least 2; nothing less makes any
  // sense.
  //
  // The sphere is oriented such that the prime meridian points in the +x
  // direction.
  UvSphere(int sectors_per_turn, int slices) noexcept;

  // All points on the sphere.
  //
  // There are actually sectors_per_slice+1 sectors in each vertical slice of
  // the sphere. The extra column of vertices is necessary to ensure the last
  // stack has correct texture mapping. You will need to set your texture to
  // GL_REPEAT in the s direction for this to work properly.
  std::vector<Coordinates> vertices;

  // The sphere's element array buffer. These elements should be drawn with
  // GL_TRIANGLES.
  std::vector<uint32_t> elements;
};

inline std::ostream& operator<<(std::ostream& out,
                                const UvSphere::Coordinates& c) noexcept {
  return out << c.DebugString();
}

}  // namespace glplanet

#endif  // GLPLANET_SRC_MESH_H_