Capturing images by callback, rather than pulling

sunshine/platform/windows/display_vram.cpp

@@ -693,6 +693,36 @@ public:
   std::vector<hwdevice_t *> *hwdevices_p;
 };
 
+capture_e display_vram_t::capture(snapshot_cb_t &&snapshot_cb, std::shared_ptr<::platf::img_t> img, bool *cursor) {
+  auto next_frame = std::chrono::steady_clock::now();
+
+  while(img) {
+    auto now = std::chrono::steady_clock::now();
+    while(next_frame > now) {
+      now = std::chrono::steady_clock::now();
+    }
+    next_frame = now + delay;
+
+    auto status = snapshot(img.get(), 1000ms, *cursor);
+    switch(status) {
+    case platf::capture_e::reinit:
+    case platf::capture_e::error:
+      return status;
+    case platf::capture_e::timeout:
+      std::this_thread::sleep_for(1ms);
+      continue;
+    case platf::capture_e::ok:
+      img = snapshot_cb(img);
+      break;
+    default:
+      BOOST_LOG(error) << "Unrecognized capture status ["sv << (int)status << ']';
+      return status;
+    }
+  }
+
+  return capture_e::ok;
+}
+
 capture_e display_vram_t::snapshot(platf::img_t *img_base, std::chrono::milliseconds timeout, bool cursor_visible) {
   auto img = (img_d3d_t *)img_base;