WebVR: add angular velocity estimate to pose

chrome/browser/android/vr_shell/vr_shell.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/android/vr_shell/vr_shell.h"
 
 #include <android/native_window_jni.h>
 
 #include <string>
 #include <utility>
 
 #include "base/android/jni_string.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/values.h"
 #include "chrome/browser/android/tab_android.h"
 #include "chrome/browser/android/vr_shell/android_ui_gesture_target.h"
 #include "chrome/browser/android/vr_shell/vr_compositor.h"
 #include "chrome/browser/android/vr_shell/vr_gl_thread.h"
 #include "chrome/browser/android/vr_shell/vr_input_manager.h"
+#include "chrome/browser/android/vr_shell/vr_math.h"
 #include "chrome/browser/android/vr_shell/vr_shell_delegate.h"
 #include "chrome/browser/android/vr_shell/vr_shell_gl.h"
 #include "chrome/browser/android/vr_shell/vr_usage_monitor.h"
 #include "chrome/browser/android/vr_shell/vr_web_contents_observer.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/content_features.h"
@@ skipping 613 matching lines @@
   }
 }
 
 void VrShell::RegisterGamepadDataFetcher(
     device::GvrGamepadDataFetcher* fetcher) {
   DVLOG(1) << __FUNCTION__ << "(" << fetcher << ")";
   gamepad_data_fetcher_ = fetcher;
 }
 
 /* static */
-device::mojom::VRPosePtr VrShell::VRPosePtrFromGvrPose(gvr::Mat4f head_mat) {
+device::mojom::VRPosePtr VrShell::VRPosePtrFromGvrPose(gvr::Mat4f head_mat,
+                                                       gvr::Mat4f head_mat_2,
+                                                       int64_t epsilon_nanos) {
   device::mojom::VRPosePtr pose = device::mojom::VRPose::New();
 
   pose->orientation.emplace(4);
 
   gfx::Transform inv_transform(
       head_mat.m[0][0], head_mat.m[0][1], head_mat.m[0][2], head_mat.m[0][3],
       head_mat.m[1][0], head_mat.m[1][1], head_mat.m[1][2], head_mat.m[1][3],
       head_mat.m[2][0], head_mat.m[2][1], head_mat.m[2][2], head_mat.m[2][3],
       head_mat.m[3][0], head_mat.m[3][1], head_mat.m[3][2], head_mat.m[3][3]);
 
   gfx::Transform transform;
   if (inv_transform.GetInverse(&transform)) {
     gfx::DecomposedTransform decomposed_transform;
     gfx::DecomposeTransform(&decomposed_transform, transform);
 
     pose->orientation.value()[0] = decomposed_transform.quaternion[0];
     pose->orientation.value()[1] = decomposed_transform.quaternion[1];
     pose->orientation.value()[2] = decomposed_transform.quaternion[2];
     pose->orientation.value()[3] = decomposed_transform.quaternion[3];
 
     pose->position.emplace(3);
     pose->position.value()[0] = decomposed_transform.translate[0];
     pose->position.value()[1] = decomposed_transform.translate[1];
     pose->position.value()[2] = decomposed_transform.translate[2];
   }
 
+  // The angular velocity is a 3-element vector pointing along the rotation
+  // axis with magnitude equal to rotation speed in radians/second, expressed
+  // in the seated frame of reference.
+  //
+  // The spec isn't very clear on details, clarification requested in
+  // https://github.com/w3c/webvr/issues/212 .
+  //
+  // Assuming that pose prediction is simply based on adding a time * angular
+  // velocity rotation to the pose, we can approximate the angular velocity
+  // from the difference between two successive poses. This is a first order
+  // estimate that assumes small enough rotations so that we can do linear
+  // approximation.
+  //
+  // See:
+  // https://en.wikipedia.org/wiki/Angular_velocity#Calculation_from_the_orientation_matrix
+  pose->angularVelocity.emplace(3);
+  // Assume that epsilon is nonzero since it's a compile-time constant
+  // provided by the caller.
+  double epsilon_seconds = epsilon_nanos * 1e-9;
+  gvr::Mat4f delta_mat;
+  gvr::Mat4f inverse_head_mat;
+  // Calculate difference matrix, and inverse head matrix rotation.
+  // For the inverse rotation, just transpose the 3x3 subsection.
+  for (int j = 0; j < 3; ++j) {
+    for (int i = 0; i < 3; ++i) {
+      delta_mat.m[j][i] =
+          (head_mat_2.m[j][i] - head_mat.m[j][i]) / epsilon_seconds;
+      inverse_head_mat.m[j][i] = head_mat.m[i][j];
+    }
+    delta_mat.m[j][3] = delta_mat.m[3][j] = 0.0;
+    inverse_head_mat.m[j][3] = inverse_head_mat.m[3][j] = 0.0;
+  }
+  delta_mat.m[3][3] = 1.0;
+  inverse_head_mat.m[3][3] = 1.0;
+  gvr::Mat4f omega_mat = MatrixMul(delta_mat, inverse_head_mat);
+  gvr::Vec3f omega_vec;
+  omega_vec.x = -omega_mat.m[2][1];
+  omega_vec.y = omega_mat.m[2][0];
+  omega_vec.z = -omega_mat.m[1][0];
+
+  // Rotate by inverse head matrix to bring into seated space.
+  gvr::Vec3f accel_vec = MatrixVectorRotate(inverse_head_mat, omega_vec);
+  pose->angularVelocity.value()[0] = accel_vec.x;

[billorr, 2017/03/27 17:33:53]

nit: velocity not accel?

[klausw, 2017/03/27 17:55:42]

Indeed, done.

+  pose->angularVelocity.value()[1] = accel_vec.y;
+  pose->angularVelocity.value()[2] = accel_vec.z;
   return pose;
 }
 
 /* static */
 gvr::Sizei VrShell::GetRecommendedWebVrSize(gvr::GvrApi* gvr_api) {
   // Pick a reasonable default size for the WebVR transfer surface
   // based on a downscaled 1:1 render resolution. This size will also
   // be reported to the client via CreateVRDisplayInfo as the
   // client-recommended renderWidth/renderHeight and for the GVR
   // framebuffer. If the client chooses a different size or resizes it
@@ skipping 84 matching lines @@
            jboolean reprojected_rendering) {
   return reinterpret_cast<intptr_t>(new VrShell(
       env, obj, reinterpret_cast<ui::WindowAndroid*>(content_window_android),
       content::WebContents::FromJavaWebContents(ui_web_contents),
       reinterpret_cast<ui::WindowAndroid*>(ui_window_android), for_web_vr,
       VrShellDelegate::GetNativeVrShellDelegate(env, delegate),
       reinterpret_cast<gvr_context*>(gvr_api), reprojected_rendering));
 }
 
 }  // namespace vr_shell