Implementation of elbow model for the controller position and rotation.

chrome/browser/android/vr_shell/elbow_model.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.
+
+// Adapted from:
+// https://github.com/googlevr/gvr-unity-sdk/blob/master/Samples/DaydreamLabsControllerPlayground/Assets/GoogleVR/Scripts/Controller/GvrArmModel.cs
+
+#include "chrome/browser/android/vr_shell/elbow_model.h"
+
+#include <cmath>
+
+#include "chrome/browser/android/vr_shell/vr_math.h"
+
+namespace vr_shell {
+
+namespace {
+
+constexpr gvr::Quatf kNoRotation = {0.f, 0.f, 0.f, 1.f};
+constexpr gvr::Vec3f kDefaultShoulderRight = {0.19f, -0.19f, 0.03f};
+constexpr float kFadeDistanceFromFace = 0.34f;
+constexpr gvr::Vec3f kDefaultRelativeElbow = {0.195f, -0.5f, 0.075f};
+constexpr gvr::Vec3f kDefaultRelativeWrist = {0.f, 0.f, -0.25f};
+constexpr gvr::Vec3f kForward = {0.f, 0.f, -1.f};
+constexpr gvr::Vec3f kUp = {0.f, 1.f, 0.f};
+constexpr float kMinExtensionAngle = 7.f;
+constexpr float kMaxExtenstionAngle = 60.f;
+constexpr float kExtensionWeight = 0.4f;
+constexpr float kDeltaAlpha = 3.f;
+
+}  // namespace
+
+ElbowModel::ElbowModel(gvr_controller_handedness handedness)
+    : handedness_(handedness), alpha_value_(1.f), torso_direction_{0, 0, 0} {}
+
+ElbowModel::~ElbowModel() = default;
+
+void ElbowModel::UpdateHandedness() {
+  handed_multiplier_ = {handedness_ == GVR_CONTROLLER_RIGHT_HANDED ? 1.f : -1.f,
+                        1.f, 1.f};
+  shoulder_rotation_ = kNoRotation;
+  shoulder_position_ =
+      PointwiseVectorMul(kDefaultShoulderRight, handed_multiplier_);
+}
+
+void ElbowModel::Update(const UpdateData& update) {
+  UpdateHandedness();
+  UpdateTorsoDirection(update);
+  ApplyArmModel(update);
+  UpdateTransparency(update);
+}
+
+void ElbowModel::UpdateTorsoDirection(const UpdateData& update) {
+  auto head_direction = update.head_direction;
+  head_direction.y = 0;
+  NormalizeVector(head_direction);
+
+  // Determine the gaze direction horizontally.
+  float angular_velocity = VectorLength(update.gyro);
+  float gaze_filter_strength =
+      Clampf((angular_velocity - .2f) / 45.f, 0.f, 0.1f);

[cjgrant, 2017/04/03 19:24:59]

0.2f here (and everywhere please).  Ie, not .2f or 2.f 

[acondor_, 2017/04/19 18:44:27]

Done.

+  torso_direction_ =
+      QuatSlerp(torso_direction_, head_direction, gaze_filter_strength);
+
+  // Rotate the fixed joints.
+  auto gaze_rotation = FromToRotation(kForward, torso_direction_);
+  shoulder_rotation_ = gaze_rotation;
+  shoulder_position_ =
+      MatrixVectorRotate(QuatToMatrix(gaze_rotation), shoulder_position_);
+}
+
+void ElbowModel::ApplyArmModel(const UpdateData& update) {
+  // Controller's orientation relative to the player.

[cjgrant, 2017/04/03 19:24:59]

s/player/user/ everywhere?

[acondor_, 2017/04/19 18:44:27]

Done.

+  auto controller_orientation = update.orientation;
+  controller_orientation =
+      QuatMultiply(QuatInverted(shoulder_rotation_), controller_orientation);
+
+  // Relative positions of the joints.
+  elbow_position_ =
+      PointwiseVectorMul(kDefaultRelativeElbow, handed_multiplier_);
+  wrist_position_ =
+      PointwiseVectorMul(kDefaultRelativeWrist, handed_multiplier_);
+  auto arm_extension_offset =
+      PointwiseVectorMul({-0.13f, 0.14f, -0.08f}, handed_multiplier_);

[cjgrant, 2017/04/03 19:24:59]

The vector here should be a constant as well.

[acondor_, 2017/04/19 18:44:27]

Done.

+
+  // Extract just the x rotation angle.
+  auto controller_forward =
+      MatrixVectorRotate(QuatToMatrix(controller_orientation), kForward);
+  float x_angle = 90.f - VectorAngleDegrees(controller_forward, kUp);
+
+  // Remove the z rotation from the controller
+  auto x_y_rotation = FromToRotation(kForward, controller_forward);
+
+  // Offset the elbow by the extension.
+  float normalized_angle = (x_angle - kMinExtensionAngle) /
+                           (kMaxExtenstionAngle - kMinExtensionAngle);
+  float extension_ratio = Clampf(normalized_angle, 0.f, 1.f);
+  elbow_position_ = VectorAdd(
+      elbow_position_, VectorScalarMul(arm_extension_offset, extension_ratio));
+
+  // Calculate the lerp interpolation factor.
+  float total_angle = QuatAngleDegrees(x_y_rotation, kNoRotation);
+  float lerp_suppresion = 1.f - pow(total_angle / 180.f, 6);
+  float lerp_value =
+      lerp_suppresion * (0.4f + 0.6f * extension_ratio * kExtensionWeight);

[asimjour1, 2017/04/19 18:58:12]

please move the magic numbers from here and define them as const with proper
name.

[acondor_, 2017/04/21 21:04:31]

Done.

+
+  // Apply the absolute rotations to the joints.
+  auto lerp_rotation = QuatLerp(kNoRotation, x_y_rotation, lerp_value);
+  elbow_rotation_ = QuatMultiply(
+      QuatMultiply(shoulder_rotation_, QuatInverted(lerp_rotation)),
+      controller_orientation);
+  wrist_rotation_ = QuatMultiply(shoulder_rotation_, controller_orientation);
+
+  // Determine the relative positions.
+  elbow_position_ =
+      MatrixVectorRotate(QuatToMatrix(shoulder_rotation_), elbow_position_);
+  wrist_position_ = VectorAdd(
+      elbow_position_,
+      MatrixVectorRotate(QuatToMatrix(elbow_rotation_), wrist_position_));
+}
+
+void ElbowModel::UpdateTransparency(const UpdateData& update) {

[asimjour1, 2017/04/19 18:58:12]

IIUC alpha_value/opacity can be obtained from the position, so it can be
calculated inside of the renderer. I don't see any reason to manage the opacity
inside of the elbow model.

[acondor_, 2017/04/21 21:04:31]

Actually, this is an animation (so it depends on time, not just distance). The
renderer is not supposed to know about time, unless we change that.

+  float distance_to_face = VectorLength(wrist_position_);
+  float alpha_change = kDeltaAlpha * update.delta_time_seconds;
+  alpha_value_ = Clampf(distance_to_face < kFadeDistanceFromFace
+                            ? alpha_value_ - alpha_change
+                            : alpha_value_ + alpha_change,
+                        0.f, 1.f);
+}
+
+}  // namespace vr_shell