add plugin camera desktop

plugins/camera_desktop/linux/photo_handler.cc

@@ -0,0 +1,72 @@
+#include "photo_handler.h"
+
+#include <gio/gio.h>
+#include <gst/app/gstappsink.h>
+#include <gst/video/video.h>
+
+#include <cstdio>
+
+bool PhotoHandler::TakePicture(GstElement* appsink,
+                               const std::string& output_path,
+                               GError** error) {
+  if (!appsink) {
+    g_set_error(error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                "Appsink is null, camera not initialized");
+    return false;
+  }
+
+  // Use the last-sample property (read-only) to avoid consumer conflicts
+  // with the preview stream.
+  GstSample* sample = nullptr;
+  g_object_get(appsink, "last-sample", &sample, nullptr);
+  if (!sample) {
+    g_set_error(error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                "No frame available for capture");
+    return false;
+  }
+
+  // Convert the RGBA sample to JPEG.
+  GstCaps* jpeg_caps = gst_caps_from_string("image/jpeg");
+  GError* convert_error = nullptr;
+  GstSample* converted = gst_video_convert_sample(
+      sample, jpeg_caps, GST_SECOND * 5, &convert_error);
+  gst_caps_unref(jpeg_caps);
+  gst_sample_unref(sample);
+
+  if (!converted) {
+    g_propagate_error(error, convert_error);
+    return false;
+  }
+
+  // Extract the JPEG buffer and write to file.
+  GstBuffer* buffer = gst_sample_get_buffer(converted);
+  GstMapInfo map;
+  if (!gst_buffer_map(buffer, &map, GST_MAP_READ)) {
+    gst_sample_unref(converted);
+    g_set_error(error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                "Failed to map JPEG buffer");
+    return false;
+  }
+
+  FILE* file = fopen(output_path.c_str(), "wb");
+  if (!file) {
+    gst_buffer_unmap(buffer, &map);
+    gst_sample_unref(converted);
+    g_set_error(error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                "Failed to open output file: %s", output_path.c_str());
+    return false;
+  }
+
+  size_t written = fwrite(map.data, 1, map.size, file);
+  fclose(file);
+  gst_buffer_unmap(buffer, &map);
+  gst_sample_unref(converted);
+
+  if (written != map.size) {
+    g_set_error(error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                "Incomplete write to output file");
+    return false;
+  }
+
+  return true;
+}