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+// 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_