Add Photonlib (#231)

Merges Photonlib into Photonvision, along with the Photonlib code examples. Also creates a new PhotonTargeting library teams can depend on.

photon-lib/src/main/native/include/photonlib/Packet.h

@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) Photon Vision.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <algorithm>
+#include <string>
+#include <vector>
+
+#include <wpi/Endian.h>
+
+namespace photonlib {
+
+/**
+ * A packet that holds byte-packed data to be sent over NetworkTables.
+ */
+class Packet {
+ public:
+  /**
+   * Constructs an empty packet.
+   */
+  Packet() = default;
+
+  /**
+   * Constructs a packet with the given data.
+   * @param data The packet data.
+   */
+  explicit Packet(std::vector<char> data) : packetData(data) {}
+
+  /**
+   * Clears the packet and resets the read and write positions.
+   */
+  void Clear() {
+    packetData.clear();
+    readPos = 0;
+    writePos = 0;
+  }
+
+  /**
+   * Returns the packet data.
+   * @return The packet data.
+   */
+  const std::vector<char>& GetData() { return packetData; }
+
+  /**
+   * Returns the number of bytes in the data.
+   * @return The number of bytes in the data.
+   */
+  size_t GetDataSize() const { return packetData.size(); }
+
+  /**
+   * Adds a value to the data buffer. This should only be used with PODs.
+   * @tparam T The data type.
+   * @param src The data source.
+   * @return A reference to the current object.
+   */
+  template <typename T>
+  Packet& operator<<(T src) {
+    packetData.resize(packetData.size() + sizeof(T));
+    std::memcpy(packetData.data() + writePos, &src, sizeof(T));
+
+    if constexpr (wpi::support::endian::system_endianness() ==
+                  wpi::support::endianness::little) {
+      // Reverse to big endian for network conventions.
+      std::reverse(packetData.data() + writePos,
+                   packetData.data() + writePos + sizeof(T));
+    }
+
+    writePos += sizeof(T);
+    return *this;
+  }
+
+  /**
+   * Extracts a value to the provided destination.
+   * @tparam T The type of value to extract.
+   * @param value The value to extract.
+   * @return A reference to the current object.
+   */
+  template <typename T>
+  Packet& operator>>(T& value) {
+    std::memcpy(&value, packetData.data() + readPos, sizeof(T));
+
+    if constexpr (wpi::support::endian::system_endianness() ==
+                  wpi::support::endianness::little) {
+      // Reverse to little endian for host.
+      char& raw = reinterpret_cast<char&>(value);
+      std::reverse(&raw, &raw + sizeof(T));
+    }
+
+    readPos += sizeof(T);
+    return *this;
+  }
+
+  bool operator==(const Packet& right) const {
+    return packetData == right.packetData;
+  }
+  bool operator!=(const Packet& right) const { return !operator==(right); }
+
+ private:
+  // Data stored in the packet
+  std::vector<char> packetData;
+
+  size_t readPos = 0;
+  size_t writePos = 0;
+};
+
+}  // namespace photonlib