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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_
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