[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/hardware/Encoder.cpp

@@ -0,0 +1,165 @@
+/*----------------------------------------------------------------------------*/
+/* 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/hardware/Encoder.h"
+
+#include <imgui.h>
+
+#include "glass/Context.h"
+#include "glass/DataSource.h"
+
+using namespace glass;
+
+void EncoderModel::SetName(const wpi::Twine& name) {
+  if (name.str().empty()) {
+    if (auto distancePerPulse = GetDistancePerPulseData()) {
+      distancePerPulse->SetName("");
+    }
+    if (auto count = GetCountData()) {
+      count->SetName("");
+    }
+    if (auto period = GetPeriodData()) {
+      period->SetName("");
+    }
+    if (auto direction = GetDirectionData()) {
+      direction->SetName("");
+    }
+    if (auto distance = GetDistanceData()) {
+      distance->SetName("");
+    }
+    if (auto rate = GetRateData()) {
+      rate->SetName("");
+    }
+  } else {
+    if (auto distancePerPulse = GetDistancePerPulseData()) {
+      distancePerPulse->SetName(name + " Distance/Count");
+    }
+    if (auto count = GetCountData()) {
+      count->SetName(name + " Count");
+    }
+    if (auto period = GetPeriodData()) {
+      period->SetName(name + " Period");
+    }
+    if (auto direction = GetDirectionData()) {
+      direction->SetName(name + " Direction");
+    }
+    if (auto distance = GetDistanceData()) {
+      distance->SetName(name + " Distance");
+    }
+    if (auto rate = GetRateData()) {
+      rate->SetName(name + " Rate");
+    }
+  }
+}
+
+void glass::DisplayEncoder(EncoderModel* model) {
+  if (auto simDevice = model->GetSimDevice()) {
+    ImGui::PushStyleColor(ImGuiCol_Text, IM_COL32(96, 96, 96, 255));
+    ImGui::TextUnformatted(simDevice);
+    ImGui::PopStyleColor();
+    return;
+  }
+
+  int chA = model->GetChannelA();
+  int chB = model->GetChannelB();
+
+  // build header label
+  std::string* name = GetStorage().GetStringRef("name");
+  char label[128];
+  if (!name->empty()) {
+    std::snprintf(label, sizeof(label), "%s [%d,%d]###name", name->c_str(), chA,
+                  chB);
+  } else {
+    std::snprintf(label, sizeof(label), "Encoder[%d,%d]###name", chA, chB);
+  }
+
+  // header
+  bool open = CollapsingHeader(label);
+
+  // context menu to change name
+  if (PopupEditName("name", name)) {
+    model->SetName(name->c_str());
+  }
+
+  if (!open) return;
+
+  ImGui::PushItemWidth(ImGui::GetFontSize() * 8);
+  // distance per pulse
+  if (auto distancePerPulseData = model->GetDistancePerPulseData()) {
+    double value = distancePerPulseData->GetValue();
+    distancePerPulseData->LabelText("Dist/Count", "%.6f", value);
+  }
+
+  // count
+  if (auto countData = model->GetCountData()) {
+    int value = countData->GetValue();
+    if (ImGui::InputInt("##input", &value)) model->SetCount(value);
+    ImGui::SameLine();
+    if (ImGui::Button("Reset")) {
+      model->SetCount(0);
+    }
+    ImGui::SameLine();
+    ImGui::Selectable("Count");
+    countData->EmitDrag();
+  }
+
+  // max period
+  {
+    double maxPeriod = model->GetMaxPeriod();
+    ImGui::LabelText("Max Period", "%.6f", maxPeriod);
+  }
+
+  // period
+  if (auto periodData = model->GetPeriodData()) {
+    double value = periodData->GetValue();
+    if (periodData->InputDouble("Period", &value, 0, 0, "%.6g")) {
+      model->SetPeriod(value);
+    }
+  }
+
+  // reverse direction
+  ImGui::LabelText("Reverse Direction", "%s",
+                   model->GetReverseDirection() ? "true" : "false");
+
+  // direction
+  if (auto directionData = model->GetDirectionData()) {
+    static const char* options[] = {"reverse", "forward"};
+    int value = directionData->GetValue() ? 1 : 0;
+    if (directionData->Combo("Direction", &value, options, 2)) {
+      model->SetDirection(value != 0);
+    }
+  }
+
+  // distance
+  if (auto distanceData = model->GetDistanceData()) {
+    double value = distanceData->GetValue();
+    if (distanceData->InputDouble("Distance", &value, 0, 0, "%.6g")) {
+      model->SetDistance(value);
+    }
+  }
+
+  // rate
+  if (auto rateData = model->GetRateData()) {
+    double value = rateData->GetValue();
+    if (rateData->InputDouble("Rate", &value, 0, 0, "%.6g")) {
+      model->SetRate(value);
+    }
+  }
+  ImGui::PopItemWidth();
+}
+
+void glass::DisplayEncoders(EncodersModel* model, wpi::StringRef noneMsg) {
+  bool hasAny = false;
+  model->ForEachEncoder([&](EncoderModel& encoder, int i) {
+    hasAny = true;
+    PushID(i);
+    DisplayEncoder(&encoder);
+    PopID();
+  });
+  if (!hasAny && !noneMsg.empty())
+    ImGui::TextUnformatted(noneMsg.begin(), noneMsg.end());
+}