Add struct_traits and typemap for blink::WebGamepad

device/gamepad/public/interfaces/gamepad_struct_traits.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 "device/gamepad/public/interfaces/gamepad_struct_traits.h"
+
+namespace mojo {
+
+// static
+void StructTraits<
+    device::mojom::GamepadQuaternionDataView,
+    blink::WebGamepadQuaternion>::SetToNull(blink::WebGamepadQuaternion* out) {
+  memset(out, 0, sizeof(blink::WebGamepadQuaternion));
+  out->notNull = false;
+}
+
+// static
+bool StructTraits<device::mojom::GamepadQuaternionDataView,
+                  blink::WebGamepadQuaternion>::
+    Read(device::mojom::GamepadQuaternionDataView data,
+         blink::WebGamepadQuaternion* out) {
+  memset(out, 0, sizeof(blink::WebGamepadQuaternion));

[yzshen1, 2016/11/16 19:20:18]

why is this needed?

[ke.he, 2016/11/17 05:51:48]

Done.

+  out->notNull = true;
+  out->x = data.x();
+  out->y = data.y();
+  out->z = data.z();
+  out->w = data.w();
+  return true;
+}
+
+// static
+void StructTraits<device::mojom::GamepadVectorDataView,
+                  blink::WebGamepadVector>::SetToNull(blink::WebGamepadVector*
+                                                          out) {
+  memset(out, 0, sizeof(blink::WebGamepadVector));
+  out->notNull = false;
+}
+
+// static
+bool StructTraits<
+    device::mojom::GamepadVectorDataView,
+    blink::WebGamepadVector>::Read(device::mojom::GamepadVectorDataView data,
+                                   blink::WebGamepadVector* out) {
+  memset(out, 0, sizeof(blink::WebGamepadVector));

[yzshen1, 2016/11/16 19:20:18]

ditto

[ke.he, 2016/11/17 05:51:48]

Done.

+  out->notNull = true;
+  out->x = data.x();
+  out->y = data.y();
+  out->z = data.z();
+  return true;
+}
+
+// static
+bool StructTraits<
+    device::mojom::GamepadButtonDataView,
+    blink::WebGamepadButton>::Read(device::mojom::GamepadButtonDataView data,
+                                   blink::WebGamepadButton* out) {
+  memset(out, 0, sizeof(blink::WebGamepadButton));

[yzshen1, 2016/11/16 19:20:18]

ditto

[ke.he, 2016/11/17 05:51:48]

Done.

+  out->pressed = data.pressed();
+  out->touched = data.touched();
+  out->value = data.value();
+  return true;
+}
+
+// static
+void StructTraits<device::mojom::GamepadPoseDataView,
+                  blink::WebGamepadPose>::SetToNull(blink::WebGamepadPose*
+                                                        out) {
+  memset(out, 0, sizeof(blink::WebGamepadPose));
+  out->notNull = false;
+}
+
+// static
+bool StructTraits<device::mojom::GamepadPoseDataView, blink::WebGamepadPose>::
+    Read(device::mojom::GamepadPoseDataView data, blink::WebGamepadPose* out) {
+  memset(out, 0, sizeof(blink::WebGamepadPose));

[yzshen1, 2016/11/16 19:20:18]

ditto

[ke.he, 2016/11/17 05:51:49]

Done.

+  out->notNull = true;
+  if (!data.ReadOrientation(&out->orientation)) {
+    return false;
+  }
+  out->hasOrientation = out->orientation.notNull;
+
+  if (!data.ReadPosition(&out->position)) {
+    return false;
+  }
+  out->hasPosition = out->position.notNull;
+
+  if (!data.ReadAngularVelocity(&out->angularVelocity)) {
+    return false;
+  }
+  if (!data.ReadLinearVelocity(&out->linearVelocity)) {
+    return false;
+  }
+  if (!data.ReadAngularAcceleration(&out->angularAcceleration)) {
+    return false;
+  }
+  if (!data.ReadLinearAcceleration(&out->linearAcceleration)) {
+    return false;
+  }
+  return true;
+}
+
+// static
+device::mojom::GamepadHand
+EnumTraits<device::mojom::GamepadHand, blink::WebGamepadHand>::ToMojom(
+    blink::WebGamepadHand input) {
+  switch (input) {
+    case blink::WebGamepadHand::GamepadHandNone:
+      return device::mojom::GamepadHand::GamepadHandNone;
+    case blink::WebGamepadHand::GamepadHandLeft:
+      return device::mojom::GamepadHand::GamepadHandLeft;
+    case blink::WebGamepadHand::GamepadHandRight:
+      return device::mojom::GamepadHand::GamepadHandRight;
+  }
+
+  NOTREACHED();
+  return device::mojom::GamepadHand::GamepadHandNone;
+}
+
+// static
+bool EnumTraits<device::mojom::GamepadHand, blink::WebGamepadHand>::FromMojom(
+    device::mojom::GamepadHand input,
+    blink::WebGamepadHand* output) {
+  switch (input) {
+    case device::mojom::GamepadHand::GamepadHandNone:
+      *output = blink::WebGamepadHand::GamepadHandNone;
+      return true;
+    case device::mojom::GamepadHand::GamepadHandLeft:
+      *output = blink::WebGamepadHand::GamepadHandLeft;
+      return true;
+    case device::mojom::GamepadHand::GamepadHandRight:
+      *output = blink::WebGamepadHand::GamepadHandRight;
+      return true;
+  }
+
+  NOTREACHED();
+  return false;
+}
+
+// static
+ConstCArray<uint16_t>
+StructTraits<device::mojom::GamepadDataView, blink::WebGamepad>::id(
+    const blink::WebGamepad& r) {
+  size_t id_length = 0;
+  while (r.id[id_length] != 0 && id_length < blink::WebGamepad::idLengthCap) {

[yzshen1, 2016/11/16 19:20:18]

You need to swap the position of the two conditions to avoid out-of-bound
access.

Besides, I don't know much about Gamepad, I don't know whether the first 0 marks
the end of id. So this needs to be reviewed by some expert.

[ke.he, 2016/11/17 05:51:48]

blundell@, I think it is correct way to check the end of id[] and mapping[] by
"r.id[id_length] != 0",
Could you PTAL at this? Thanks.

[blundell, 2016/11/17 14:55:41]

I'm not a domain expert on Gamepad either, but this (and the below) look correct
to me based on
https://cs.chromium.org/chromium/src/device/gamepad/gamepad_platform_data_fet....

bajones@ or scottmg@ should be able to definitively confirm.

+    id_length++;
+  }
+  return {id_length, reinterpret_cast<const uint16_t*>(&r.id[0])};
+}
+
+// static
+ConstCArray<uint16_t>
+StructTraits<device::mojom::GamepadDataView, blink::WebGamepad>::mapping(
+    const blink::WebGamepad& r) {
+  size_t mapping_length = 0;
+  while (r.mapping[mapping_length] != 0 &&

[yzshen1, 2016/11/16 19:20:18]

ditto

[ke.he, 2016/11/17 05:51:48]

Done.

+         mapping_length < blink::WebGamepad::mappingLengthCap) {
+    mapping_length++;
+  }
+  return {mapping_length, reinterpret_cast<const uint16_t*>(&r.mapping[0])};
+}
+
+// static
+bool StructTraits<device::mojom::GamepadDataView, blink::WebGamepad>::Read(
+    device::mojom::GamepadDataView data,
+    blink::WebGamepad* out) {
+  memset(out, 0, sizeof(blink::WebGamepad));

[yzshen1, 2016/11/16 19:20:18]

Does it make sense to only memset those necessary fields, i.e., id/mapping?

Usually I would avoid memseting an object's contents directly.

[ke.he, 2016/11/17 05:51:48]

Yes, it make sense to only memset necessary fields.
Mojo didn't do memset before it passes "out" into Read(). the out are filled
with random data.
But I noticed all the members will be assigned so it is OK to skip the memset
whole object, and only memset necessary fields.
It is more efficient in this way.

Done.

+  out->connected = data.connected();
+
+  CArray<uint16_t> id = {0, blink::WebGamepad::idLengthCap,
+                         reinterpret_cast<uint16_t*>(&out->id[0])};
+  if (!data.ReadId(&id)) {
+    return false;
+  }
+
+  out->timestamp = data.timestamp();
+
+  CArray<double> axes = {0, blink::WebGamepad::axesLengthCap, &out->axes[0]};
+  if (!data.ReadAxes(&axes)) {
+    return false;
+  }
+  // static_cast is safe when "data.ReadAxes(&axes)" above returns true.
+  out->axesLength = static_cast<unsigned>(axes.size);
+
+  CArray<blink::WebGamepadButton> buttons = {
+      0, blink::WebGamepad::buttonsLengthCap, &out->buttons[0]};
+  if (!data.ReadButtons(&buttons)) {
+    return false;
+  }
+  // static_cast is safe when "data.ReadButtons(&buttons)" above returns true.
+  out->buttonsLength = static_cast<unsigned>(buttons.size);
+
+  CArray<uint16_t> mapping = {0, blink::WebGamepad::mappingLengthCap,
+                              reinterpret_cast<uint16_t*>(&out->mapping[0])};
+
+  if (!data.ReadMapping(&mapping)) {
+    return false;
+  }
+
+  if (!data.ReadPose(&out->pose)) {
+    return false;
+  }
+
+  blink::WebGamepadHand hand;
+  if (!data.ReadHand(&hand)) {
+    return false;
+  }
+  out->hand = hand;
+
+  out->displayId = data.display_id();
+
+  return true;
+}
+
+}  // namespace mojo