WebXR depth: make XRDepthData a union

CL followup - make XRDepthData into an union so that it is possible
to express that the data sent over mojom boundary is either still valid,
or that new data has arrived.

For discussion, see:
https://crrev.com/c/2391619/comment/177fee99_a1338219/

Change-Id: I240357a32dc7fadcae379c3b5f1ca29bdeffcb6c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417570Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809471}

device/vr/android/arcore/arcore_impl.cc

@@ -1501,11 +1501,11 @@ mojom::XRDepthDataPtr ArCoreImpl::GetDepthData() {
   CHECK_EQ(num_planes, 1) << "Depth image must have 1 plane, found: "
                           << num_planes;
 
-  mojom::XRDepthDataPtr result = mojom::XRDepthData::New();
+  if (time_delta > previous_depth_data_time_) {
+    mojom::XRDepthDataUpdatedPtr result = mojom::XRDepthDataUpdated::New();
 
-  result->time_delta = time_delta;
+    result->time_delta = time_delta;
 
-  if (time_delta > previous_depth_data_time_) {
     int32_t width = 0, height = 0;
     ArImage_getWidth(arcore_session_.get(), ar_image.get(), &width);
     ArImage_getHeight(arcore_session_.get(), ar_image.get(), &height);
@@ -1540,12 +1540,15 @@ mojom::XRDepthDataPtr ArCoreImpl::GetDepthData() {
     result->size = gfx::Size(width, height);
 
     DVLOG(3) << __func__ << ": norm_texture_from_norm_view=\n"
-             << result->norm_texture_from_norm_view->ToString();
+             << result->norm_texture_from_norm_view.ToString();
 
     previous_depth_data_time_ = time_delta;
+
+    return mojom::XRDepthData::NewUpdatedDepthData(std::move(result));
   }
 
-  return result;
+  return mojom::XRDepthData::NewDataStillValid(
+      mojom::XRDepthDataStillValid::New());
 }
 
 bool ArCoreImpl::IsOnGlThread() const {

device/vr/public/mojom/vr_service.mojom

@@ -537,24 +537,36 @@ struct XRLightEstimationData {
   XRReflectionProbe? reflection_probe;
 };
 
-struct XRDepthData {
-  // Timestamp of the returned data, in unspecified base. In case the data is
-  // equal to the one returned on a previous frame (for example because the
-  // latest depth data is unavailable), the pixel_data member will be null and
-  // the timestamp will match the timestamp of the previously returned depth
-  // data.
+// Structure that signifies that the depth data is still valid, no additional
+// information is provided. See |XRDepthData| for more details.
+struct XRDepthDataStillValid {};
+
+// Structure that signifies that the Depth data was updated. Provides
+// information about current depth data. See |XRDepthData| for more details.
+struct XRDepthDataUpdated {
+  // Timestamp of the returned data, in unspecified base.
   mojo_base.mojom.TimeDelta time_delta;
   // Array of 16-bit numbers representing depth in millimeters from the camera
   // plane.
-  mojo_base.mojom.BigBuffer? pixel_data;
+  mojo_base.mojom.BigBuffer pixel_data;
   // Transform that needs to be applied when indexing into pixel_data when using
   // normalized view coordinates (with origin at bottom left corner of the
   // screen).
-  gfx.mojom.Transform? norm_texture_from_norm_view;
+  gfx.mojom.Transform norm_texture_from_norm_view;
   // Size of the pixel array. Valid iff pixel_data is not null.
   gfx.mojom.Size size;
 };
 
+// Depth data may be the same as the one returned in the previous frame - it is
+// represented as a union of (empty) XRDepthDataStillValid structure that
+// conveys no additional information except that the previously returned depth
+// data is still valid, and the XRDepthDataUpdated structure that signifies that
+// the depth data was updated & carries all information about it.
+union XRDepthData {
+  XRDepthDataStillValid data_still_valid;
+  XRDepthDataUpdated updated_depth_data;
+};
+
 // The data needed for each animation frame of an XRSession.
 struct XRFrameData {
   // General XRSession value
@@ -575,7 +587,8 @@ struct XRFrameData {
 
   // Depth data (if the device supports it and the environment integration is
   // enabled). This assumes that depth information is provided from a single
-  // sensor.
+  // sensor. If for any reason the latest depth data could not be obtained, it
+  // will be set to null.
   XRDepthData? depth_data;
 
   // Indicates that there has been a significant discontinuity in the mojo space

third_party/blink/renderer/modules/xr/xr_depth_information.cc

@@ -21,20 +21,20 @@ constexpr char kOutOfBoundsAccess[] =
 namespace blink {
 
 XRDepthInformation::XRDepthInformation(
-    const device::mojom::blink::XRDepthData& depth_data)
+    const device::mojom::blink::XRDepthDataUpdated& depth_data)
     : width_(depth_data.size.width()),
       height_(depth_data.size.height()),
-      norm_texture_from_norm_view_(*depth_data.norm_texture_from_norm_view) {
+      norm_texture_from_norm_view_(depth_data.norm_texture_from_norm_view) {
   DVLOG(3) << __func__ << ": width_=" << width_ << ", height_=" << height_
            << ", norm_texture_from_norm_view_="
            << norm_texture_from_norm_view_.ToString();
 
   CHECK_EQ(base::CheckMul(2, width_, height_).ValueOrDie(),
-           depth_data.pixel_data->size());
+           depth_data.pixel_data.size());
 
   base::span<const uint16_t> pixel_data = base::make_span(
-      reinterpret_cast<const uint16_t*>(depth_data.pixel_data->data()),
-      depth_data.pixel_data->size() / 2);
+      reinterpret_cast<const uint16_t*>(depth_data.pixel_data.data()),
+      depth_data.pixel_data.size() / 2);
 
   // Copy the underlying pixel data into DOMUint16Array:
   data_ = DOMUint16Array::Create(pixel_data.data(), pixel_data.size());

third_party/blink/renderer/modules/xr/xr_depth_information.h

@@ -21,7 +21,7 @@ class XRDepthInformation final : public ScriptWrappable {
 
  public:
   explicit XRDepthInformation(
-      const device::mojom::blink::XRDepthData& depth_data);
+      const device::mojom::blink::XRDepthDataUpdated& depth_data);
 
   DOMUint16Array* data() const;
 

third_party/blink/renderer/modules/xr/xr_session.cc

@@ -1154,14 +1154,23 @@ void XRSession::ProcessDepthData(
     device::mojom::blink::XRDepthDataPtr depth_data) {
   DVLOG(3) << __func__ << ": depth_data valid? " << !!depth_data;
 
-  if (depth_data && depth_data->pixel_data) {
-    // Just store the current depth data as a member - we will need to construct
-    // instances of XRDepthInformation once the app requests them anyway.
-    depth_data_ = std::move(depth_data);
+  if (depth_data) {
+    switch (depth_data->which()) {
+      case device::mojom::blink::XRDepthData::Tag::DATA_STILL_VALID:
+        // Stale depth buffer is still the most recent information we have.
+        // Current API shape is not well-suited to return data pertaining to
+        // older frames, so just discard what we have.
+        depth_data_ = nullptr;
+        break;
+      case device::mojom::blink::XRDepthData::Tag::UPDATED_DEPTH_DATA:
+        // Just store the current depth data as a member - we will need to
+        // construct instances of XRDepthInformation once the app requests them
+        // anyway.
+        depth_data_ = std::move(depth_data->get_updated_depth_data());
+        break;
+    }
   } else {
-    // Device did not return new pixel data - stale depth buffer is still the
-    // most recent information we have. Current API shape is not well-suited to
-    // return data pertaining to older frames, so just discard what we have.
+    // Device did not return new pixel data.
     depth_data_ = nullptr;
   }
 }

third_party/blink/renderer/modules/xr/xr_session.h

@@ -553,7 +553,7 @@ class XRSession final
   std::unique_ptr<TransformationMatrix> mojo_from_viewer_;
 
   // Current depth data buffer.
-  device::mojom::blink::XRDepthDataPtr depth_data_;
+  device::mojom::blink::XRDepthDataUpdatedPtr depth_data_;
 
   bool pending_frame_ = false;
   bool resolving_frame_ = false;