[glass] Add glass: an application for display of robot data

This reuses many pieces of the current simulation GUI.  The common pieces have
been refactored into the libglass library.

The libglass library is designed to be usable for other standalone data
visualization applications (e.g. viewing data logs).

The name "glass" comes from "glass cockpit", as the application features
several multi-function displays that can be adjusted to display robot
information as needed.

glass/src/lib/native/cpp/other/DeviceTree.cpp

@@ -0,0 +1,161 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "glass/other/DeviceTree.h"
+
+#include <cinttypes>
+
+#include <imgui.h>
+
+#include "glass/Context.h"
+#include "glass/ContextInternal.h"
+#include "glass/DataSource.h"
+
+using namespace glass;
+
+void DeviceTreeModel::Update() {
+  for (auto&& display : m_displays) {
+    if (display.first) display.first->Update();
+  }
+}
+
+bool DeviceTreeModel::Exists() {
+  for (auto&& display : m_displays) {
+    if (display.first && display.first->Exists()) return true;
+  }
+  return false;
+}
+
+void DeviceTreeModel::Display() {
+  for (auto&& display : m_displays) {
+    if (display.second) display.second(display.first);
+  }
+}
+
+void glass::HideDevice(const char* id) { gContext->deviceHidden[id] = true; }
+
+bool glass::BeginDevice(const char* id, ImGuiTreeNodeFlags flags) {
+  if (gContext->deviceHidden[id]) return false;
+
+  PushID(id);
+
+  // build label
+  std::string* name = GetStorage().GetStringRef("name");
+  char label[128];
+  std::snprintf(label, sizeof(label), "%s###name",
+                name->empty() ? id : name->c_str());
+
+  bool open = CollapsingHeader(label, flags);
+  PopupEditName("name", name);
+
+  if (!open) PopID();
+  return open;
+}
+
+void glass::EndDevice() { PopID(); }
+
+static bool DeviceBooleanImpl(const char* name, bool readonly, bool* value) {
+  if (readonly) {
+    ImGui::LabelText(name, "%s", *value ? "true" : "false");
+  } else {
+    static const char* boolOptions[] = {"false", "true"};
+    int val = *value ? 1 : 0;
+    if (ImGui::Combo(name, &val, boolOptions, 2)) {
+      *value = val;
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool DeviceDoubleImpl(const char* name, bool readonly, double* value) {
+  if (readonly) {
+    ImGui::LabelText(name, "%.6f", *value);
+    return false;
+  } else {
+    return ImGui::InputDouble(name, value, 0, 0, "%.6f",
+                              ImGuiInputTextFlags_EnterReturnsTrue);
+  }
+}
+
+static bool DeviceEnumImpl(const char* name, bool readonly, int* value,
+                           const char** options, int32_t numOptions) {
+  if (readonly) {
+    if (*value < 0 || *value >= numOptions)
+      ImGui::LabelText(name, "%d (unknown)", *value);
+    else
+      ImGui::LabelText(name, "%s", options[*value]);
+    return false;
+  } else {
+    return ImGui::Combo(name, value, options, numOptions);
+  }
+}
+
+static bool DeviceIntImpl(const char* name, bool readonly, int32_t* value) {
+  if (readonly) {
+    ImGui::LabelText(name, "%" PRId32, *value);
+    return false;
+  } else {
+    return ImGui::InputScalar(name, ImGuiDataType_S32, value, nullptr, nullptr,
+                              nullptr, ImGuiInputTextFlags_EnterReturnsTrue);
+  }
+}
+
+static bool DeviceLongImpl(const char* name, bool readonly, int64_t* value) {
+  if (readonly) {
+    ImGui::LabelText(name, "%" PRId64, *value);
+    return false;
+  } else {
+    return ImGui::InputScalar(name, ImGuiDataType_S64, value, nullptr, nullptr,
+                              nullptr, ImGuiInputTextFlags_EnterReturnsTrue);
+  }
+}
+
+template <typename F, typename... Args>
+static inline bool DeviceValueImpl(const char* name, bool readonly,
+                                   const DataSource* source, F&& func,
+                                   Args... args) {
+  ImGui::SetNextItemWidth(ImGui::GetWindowWidth() * 0.5f);
+  if (!source) {
+    return func(name, readonly, args...);
+  } else {
+    ImGui::PushID(name);
+    bool rv = func("", readonly, args...);
+    ImGui::SameLine(0, ImGui::GetStyle().ItemInnerSpacing.x);
+    ImGui::Selectable(name);
+    source->EmitDrag();
+    ImGui::PopID();
+    return rv;
+  }
+}
+
+bool glass::DeviceBoolean(const char* name, bool readonly, bool* value,
+                          const DataSource* source) {
+  return DeviceValueImpl(name, readonly, source, DeviceBooleanImpl, value);
+}
+
+bool glass::DeviceDouble(const char* name, bool readonly, double* value,
+                         const DataSource* source) {
+  return DeviceValueImpl(name, readonly, source, DeviceDoubleImpl, value);
+}
+
+bool glass::DeviceEnum(const char* name, bool readonly, int* value,
+                       const char** options, int32_t numOptions,
+                       const DataSource* source) {
+  return DeviceValueImpl(name, readonly, source, DeviceEnumImpl, value, options,
+                         numOptions);
+}
+
+bool glass::DeviceInt(const char* name, bool readonly, int32_t* value,
+                      const DataSource* source) {
+  return DeviceValueImpl(name, readonly, source, DeviceIntImpl, value);
+}
+
+bool glass::DeviceLong(const char* name, bool readonly, int64_t* value,
+                       const DataSource* source) {
+  return DeviceValueImpl(name, readonly, source, DeviceLongImpl, value);
+}