add SharedMemoryWriter support

include/vizionstreamer/SharedMemoryWriter.h

@@ -0,0 +1,62 @@
+/*
+ * VizionStreamer - Shared Memory Writer Interface
+ * Copyright (c) 2025 Maik Jurischka
+ *
+ * Licensed under CC BY-NC-SA 4.0
+ * https://creativecommons.org/licenses/by-nc-sa/4.0/
+ */
+
+#pragma once
+
+#include <string>
+#include <cstdint>
+#include <atomic>
+
+// Shared memory header structure for lock-free synchronization
+struct SharedMemoryHeader {
+    uint32_t magic;                      // Magic number for validation (0x56495A4E = "VIZN")
+    uint32_t width;                      // Frame width in pixels
+    uint32_t height;                     // Frame height in pixels
+    uint32_t format;                     // Format enum (matches VX_IMAGE_FORMAT)
+    uint32_t data_size;                  // Actual frame data size in bytes
+    uint64_t timestamp_ns;               // Timestamp in nanoseconds
+    uint32_t frame_sequence;             // Monotonic frame counter
+    std::atomic<uint32_t> write_sequence; // Lock-free synchronization counter
+    char format_str[16];                 // Format string ("YUY2", "MJPG", etc.)
+    uint8_t reserved[72];                // Reserved for future expansion (padding to 128 bytes)
+};
+
+static_assert(sizeof(SharedMemoryHeader) == 128, "SharedMemoryHeader must be exactly 128 bytes");
+
+class SharedMemoryWriter {
+public:
+    explicit SharedMemoryWriter(std::string name);
+    ~SharedMemoryWriter();
+
+    // Initialize shared memory region with given buffer size
+    bool create(size_t frame_buffer_size);
+
+    // Write frame to shared memory with lock-free protocol
+    bool writeFrame(const uint8_t* data, size_t size,
+                   int width, int height,
+                   const std::string& format,
+                   uint64_t timestamp_ns = 0);
+
+    // Cleanup shared memory
+    void destroy();
+
+    // Status queries
+    bool isCreated() const { return shm_fd_ >= 0; }
+    std::string getName() const { return shm_name_; }
+    size_t getBufferSize() const { return buffer_size_; }
+    uint32_t getFrameCount() const { return frame_counter_; }
+
+private:
+    SharedMemoryHeader* getHeader();
+
+    std::string shm_name_;           // Shared memory object name
+    int shm_fd_;                     // File descriptor from shm_open
+    void* shm_ptr_;                  // Mapped memory pointer
+    size_t buffer_size_;             // Total size (header + frame data)
+    uint32_t frame_counter_;         // Frame sequence counter
+};