Adding Chrome-side WebVR interface

content/browser/vr/cardboard/cardboard_vr_device.cc

+// Copyright 2015 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 "content/browser/vr/cardboard/cardboard_vr_device.h"
+
+#include <math.h>
+#include <algorithm>
+
+#include "base/android/jni_android.h"
+#include "base/android/jni_array.h"
+#include "base/android/jni_string.h"
+#include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
+#include "base/strings/utf_string_conversions.h"
+#include "jni/CardboardVRDevice_jni.h"
+#include "ui/base/base_window.h"
+
+using base::android::AttachCurrentThread;
+
+namespace content {
+
+namespace {
+
+void MatrixToOrientationQuat(const float m[16], blink::WebVRVector4& out) {

[mdempsky, 2015/05/11 19:25:01]

Nit: Google C++ style guide disallows non-const reference parameters:
https://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Reference_Ar...

Also, are these formulas taken from somewhere?  They're non-trivial enough that
it might be nice to reference somewhere authoritative.

Lastly, I think the formulas assume m[15] == 1.0f.  Is that guaranteed to always
be true?  (I suspect it is in practice, but briefly scanning the Cardboard SDK
documentation, it doesn't seem promised.)  Is it worth adding a DCHECK or
something to verify?

[bajones, 2015/05/12 00:13:39]

Ooh... that's a really good question. This was ported from my Javascript matrix
library which was ported from one of my older C++ libraries which was evolved
from several previous versions of the same library which was referenced from I
don't even remember what anymore. Carmack is probably at the bottom of the pile
somewhere. :)

I'm happy to dig around and find a reasonably authoritative source for the
algorithm and point to it. Certainly didn't spring fully formed from my head. 
 
Good catch! I'll throw a check into here.

+  float fTrace = m[0] + m[5] + m[10];
+  float fRoot;
+  if (fTrace > 0.0f) {
+    fRoot = sqrtf(1.0f + fTrace) * 2.0f;
+    out.x = (m[9] - m[6]) / fRoot;
+    out.y = (m[2] - m[8]) / fRoot;
+    out.z = (m[4] - m[1]) / fRoot;
+    out.w = 0.25f * fRoot;
+  } else if ((m[0] > m[5]) && (m[0] > m[10])) {
+    fRoot = sqrtf(1.0f + m[0] - m[5] - m[10]) * 2.0f;
+    out.x = 0.25f * fRoot;
+    out.y = (m[1] + m[4]) / fRoot;
+    out.z = (m[2] + m[8]) / fRoot;
+    out.w = (m[9] - m[6]) / fRoot;
+  } else if (m[5] > m[10]) {
+    fRoot = sqrtf(1.0f + m[5] - m[0] - m[10]) * 2.0f;
+    out.x = (m[1] + m[4]) / fRoot;
+    out.y = 0.25f * fRoot;
+    out.z = (m[6] + m[9]) / fRoot;
+    out.w = (m[2] - m[8]) / fRoot;
+  } else {
+    fRoot = sqrtf(1.0f + m[10] - m[0] - m[5]) * 2.0f;
+    out.x = (m[2] + m[8]) / fRoot;
+    out.y = (m[6] + m[9]) / fRoot;
+    out.z = 0.25f * fRoot;
+    out.w = (m[4] - m[1]) / fRoot;
+  }
+}
+
+} // namespace
+
+bool CardboardVRDevice::RegisterCardboardVRDevice(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+CardboardVRDevice::CardboardVRDevice(VRDeviceProvider* provider)
+    : VRDevice(provider),
+    frame_index_(0) {

[jdduke (slow), 2015/04/24 21:46:07]

Would it be worth having a ThreadChecker for this class, and we can DCHECK that
each of the JNI methods are all called on the same thread?

[bajones, 2015/05/12 00:13:39]

This class is only called from the VRService, which already has a ThreadChecker
for exactly that purpose.

+  j_cardboard_device_.Reset(
+      Java_CardboardVRDevice_create(
+          AttachCurrentThread(),
+          base::android::GetApplicationContext()));
+}
+
+CardboardVRDevice::~CardboardVRDevice() {
+  Java_CardboardVRDevice_stopTracking(AttachCurrentThread(),
+                                      j_cardboard_device_.obj());
+}
+
+void CardboardVRDevice::GetVRDevice(blink::WebVRDevice* device) {
+  memset(device, 0, sizeof(blink::WebVRDevice));
+
+  device->flags = blink::WebVRDeviceTypePosition | blink::WebVRDeviceTypeHMD;
+
+  JNIEnv* env = AttachCurrentThread();
+
+  {
+    ScopedJavaLocalRef<jstring> j_device_name;
+    j_device_name = Java_CardboardVRDevice_getDeviceName(
+        env,
+        j_cardboard_device_.obj());
+
+    base::string16 tmp16;
+    base::android::ConvertJavaStringToUTF16(env, j_device_name.obj(), &tmp16);
+    tmp16.copy(device->deviceName, blink::WebVRDevice::deviceNameLengthCap - 1);
+  }
+
+  ScopedJavaLocalRef<jfloatArray> j_fov(env, env->NewFloatArray(4));
+  Java_CardboardVRDevice_getFieldOfView(env,
+                                        j_cardboard_device_.obj(),
+                                        j_fov.obj());
+
+  std::vector<float> fov;
+  base::android::JavaFloatArrayToFloatVector(env,
+                                             j_fov.obj(),
+                                             &fov);
+
+  blink::WebVRHMDInfo& hmdInfo = device->hmdInfo;
+
+  hmdInfo.leftEye.recommendedFieldOfView.upDegrees = fov[0];
+  hmdInfo.leftEye.recommendedFieldOfView.downDegrees = fov[1];
+  hmdInfo.leftEye.recommendedFieldOfView.leftDegrees = fov[2];
+  hmdInfo.leftEye.recommendedFieldOfView.rightDegrees = fov[3];
+
+  // Cardboard devices always assume a mirrored FOV, so this is just the left
+  // eye FOV with the left and right degrees swapped.
+  hmdInfo.rightEye.recommendedFieldOfView.upDegrees = fov[0];
+  hmdInfo.rightEye.recommendedFieldOfView.downDegrees = fov[1];
+  hmdInfo.rightEye.recommendedFieldOfView.leftDegrees = fov[3];
+  hmdInfo.rightEye.recommendedFieldOfView.rightDegrees = fov[2];
+
+  // Cardboard does not support configurable FOV.
+  hmdInfo.leftEye.maximumFieldOfView = hmdInfo.leftEye.recommendedFieldOfView;
+  hmdInfo.rightEye.maximumFieldOfView = hmdInfo.rightEye.recommendedFieldOfView;
+  hmdInfo.leftEye.minimumFieldOfView = hmdInfo.leftEye.recommendedFieldOfView;
+  hmdInfo.rightEye.minimumFieldOfView = hmdInfo.rightEye.recommendedFieldOfView;
+
+  float ipd = Java_CardboardVRDevice_getIpd(env, j_cardboard_device_.obj());
+
+  hmdInfo.leftEye.eyeTranslation.x = ipd * -0.5f;
+  hmdInfo.leftEye.eyeTranslation.y = 0.0f;
+  hmdInfo.leftEye.eyeTranslation.z = 0.0f;
+
+  hmdInfo.rightEye.eyeTranslation.x = ipd * 0.5f;
+  hmdInfo.rightEye.eyeTranslation.y = 0.0f;
+  hmdInfo.rightEye.eyeTranslation.z = 0.0f;
+
+  ScopedJavaLocalRef<jintArray> j_screen_size(env, env->NewIntArray(2));
+  Java_CardboardVRDevice_getScreenSize(env,
+                                       j_cardboard_device_.obj(),
+                                       j_screen_size.obj());
+
+  std::vector<int> screen_size;
+  base::android::JavaIntArrayToIntVector(env,
+                                         j_screen_size.obj(),
+                                         &screen_size);
+
+  hmdInfo.leftEye.renderRect.x = 0;
+  hmdInfo.leftEye.renderRect.y = 0;
+  hmdInfo.leftEye.renderRect.width = screen_size[0] / 2.0;
+  hmdInfo.leftEye.renderRect.height = screen_size[1];
+
+  hmdInfo.rightEye.renderRect.x = screen_size[0] / 2.0;
+  hmdInfo.rightEye.renderRect.y = 0;
+  hmdInfo.rightEye.renderRect.width = screen_size[0] / 2.0;
+  hmdInfo.rightEye.renderRect.height = screen_size[1];
+}
+
+void CardboardVRDevice::GetOrientationPosition(
+    blink::WebVRVector4& orientation,

[mdempsky, 2015/05/11 19:25:01]

Nit: Non-const reference parameters.

+    blink::WebVRVector3& position) {
+  JNIEnv* env = AttachCurrentThread();
+  ScopedJavaLocalRef<jfloatArray> j_head_matrix(env, env->NewFloatArray(16));
+  Java_CardboardVRDevice_getSensorState(env,
+                                        j_cardboard_device_.obj(),
+                                        j_head_matrix.obj());
+
+  std::vector<float> head_matrix;
+  base::android::JavaFloatArrayToFloatVector(env,
+                                             j_head_matrix.obj(),
+                                             &head_matrix);
+
+  MatrixToOrientationQuat(&head_matrix[0], orientation);
+
+  position.x = -head_matrix[12];
+  position.y = head_matrix[13];
+  position.z = head_matrix[14];
+}
+
+void CardboardVRDevice::GetSensorState(blink::WebHMDSensorState* state) {
+  memset(state, 0, sizeof(blink::WebHMDSensorState));
+
+  state->timestamp = frame_index_;
+  state->frameIndex = frame_index_;
+  state->flags = blink::WebVRSensorStateOrientation |
+                 blink::WebVRSensorStatePosition;
+
+  GetOrientationPosition(state->orientation, state->position);
+
+  frame_index_++;
+}
+
+void CardboardVRDevice::ResetSensor() {
+  Java_CardboardVRDevice_resetSensor(AttachCurrentThread(),
+                                     j_cardboard_device_.obj());
+}
+
+}  // namespace content