source: DataSource, Frame, SourceConfig and the registry (unused yet)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/source/frame.hpp

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include "model.hpp"
+
+#include <cstdint>
+
+namespace udpscope {
+
+/// One signal's values in a frame. `values` points into the source's own buffer and is valid
+/// only while the `on_data` call that received the frame is running.
+struct SignalValues {
+  const double* values = nullptr;
+  std::uint32_t count = 0;
+};
+
+/// A data frame in source-neutral form; it mirrors `udps_frame_t`. A source with no packet
+/// counter supplies a running one and `lost = 0`: the hole, backfill and time-base logic only
+/// needs `counter`, `lost` and `late`.
+struct Frame {
+  std::uint32_t counter = 0;
+  std::uint32_t lost = 0;
+  bool late = false;
+  double recv_time = 0.0;
+  std::uint8_t publish_mode = 0;
+  std::uint32_t num_samples = 0;
+  std::uint32_t num_signals = 0;
+  const SignalInfo* signals = nullptr;
+  const SignalValues* values = nullptr;
+
+  /// Element `elem` of signal `sig` at sample `sample`. Mirrors `udps_frame_value`: a scalar
+  /// signal carried once per sample is indexed by `sample`, a vector/matrix signal by `elem`.
+  /// Out of range reads 0.0.
+  double value(std::uint32_t sig, std::uint32_t sample, std::uint32_t elem) const noexcept {
+    if (sig >= num_signals) return 0.0;
+    const SignalValues& v = values[sig];
+    const std::uint32_t idx =
+        (v.count == num_samples && signals[sig].elements() == 1u) ? sample : elem;
+    return idx < v.count ? v.values[idx] : 0.0;
+  }
+};
+
+}  // namespace udpscope