From d0e18bdb7924c71cdca8dd983711171d87ef28be Mon Sep 17 00:00:00 2001
From: Benjamin Barenblat <bbarenblat@gmail.com>
Date: Mon, 17 Jan 2022 23:12:32 -0500
Subject: glplanet, an OpenGL-based planetary renderer
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glplanet draws Earth like it currently appears from space, putting
nighttime areas in shadow and daytime areas in light. It’s modeled
after Xplanet (http://xplanet.sourceforge.net/), but whereas Xplanet is
entirely a CPU-resident program, glplanet draws using OpenGL. It’s thus
much less resource-intensive, particularly when using high-resolution
textures.
---
 src/mesh.cc | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 src/mesh.cc

(limited to 'src/mesh.cc')

diff --git a/src/mesh.cc b/src/mesh.cc
new file mode 100644
index 0000000..873e74b
--- /dev/null
+++ b/src/mesh.cc
@@ -0,0 +1,72 @@
+// 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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