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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.
#include "src/mesh.h"
#include <math.h>
#include <string>
#include <vector>
#include "src/util.h"
#include "third_party/abseil/absl/strings/substitute.h"
namespace glplanet {
std::string UvSphere::Coordinates::DebugString() const noexcept {
return absl::Substitute(
"Coordinates{.x = $0, .y = $1, .z = $2, .u = $3, .v = $4}", x, y, z, u,
v);
}
UvSphere::UvSphere(int sectors_per_turn, int slices) noexcept {
DCHECK(sectors_per_turn >= 3);
DCHECK(slices >= 2);
int sectors_per_slice = sectors_per_turn + 1;
for (int j = 0; j <= slices; ++j) {
for (int i = 0; i < sectors_per_slice; ++i) {
double longitude = i * (2.0 * M_PI / sectors_per_turn) - M_PI;
double latitude = j * (M_PI / slices) - M_PI / 2.0;
vertices.push_back({
.x = static_cast<float>(cos(latitude) * cos(longitude)),
.y = static_cast<float>(cos(latitude) * sin(longitude)),
.z = sinf(latitude),
.u = static_cast<float>(i / static_cast<double>(sectors_per_turn)),
.v = static_cast<float>(1 - j / static_cast<double>(slices)),
});
}
}
// Generate triangle elements.
for (int j = 0; j < slices; ++j) {
for (int i = 0; i < sectors_per_turn; ++i) {
uint32_t ll = j * sectors_per_slice + i;
uint32_t lr = ll + 1;
uint32_t ul = ll + sectors_per_slice;
uint32_t ur = ul + 1;
DCHECK(ll < vertices.size());
DCHECK(lr < vertices.size());
DCHECK(ul < vertices.size());
DCHECK(ur < vertices.size());
elements.insert(elements.end(), {ll, ur, ul, lr, ur, ll});
}
}
}
} // namespace glplanet
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