[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/support/ExtraGuiWidgets.cpp

@@ -0,0 +1,168 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017-2020 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/support/ExtraGuiWidgets.h"
+
+#define IMGUI_DEFINE_MATH_OPERATORS
+#include <imgui_internal.h>
+
+#include "glass/DataSource.h"
+
+namespace glass {
+
+void DrawLEDSources(const int* values, DataSource** sources, int numValues,
+                    int cols, const ImU32* colors, float size, float spacing,
+                    const LEDConfig& config) {
+  if (numValues == 0 || cols < 1) return;
+  if (size == 0) size = ImGui::GetFontSize() / 2.0;
+  if (spacing == 0) spacing = ImGui::GetFontSize() / 3.0;
+
+  int rows = (numValues + cols - 1) / cols;
+  float inc = size + spacing;
+
+  ImDrawList* drawList = ImGui::GetWindowDrawList();
+  const ImVec2 p = ImGui::GetCursorScreenPos();
+
+  float sized2 = size / 2;
+  float ystart, yinc;
+  if (config.start & 1) {
+    // lower
+    ystart = p.y + sized2 + inc * (rows - 1);
+    yinc = -inc;
+  } else {
+    // upper
+    ystart = p.y + sized2;
+    yinc = inc;
+  }
+
+  float xstart, xinc;
+  if (config.start & 2) {
+    // right
+    xstart = p.x + sized2 + inc * (cols - 1);
+    xinc = -inc;
+  } else {
+    // left
+    xstart = p.x + sized2;
+    xinc = inc;
+  }
+
+  float x = xstart, y = ystart;
+  int rowcol = 1;  // row for row-major, column for column-major
+  for (int i = 0; i < numValues; ++i) {
+    if (config.order == LEDConfig::RowMajor) {
+      if (i >= (rowcol * cols)) {
+        ++rowcol;
+        if (config.serpentine) {
+          x -= xinc;
+          xinc = -xinc;
+        } else {
+          x = xstart;
+        }
+        y += yinc;
+      }
+    } else {
+      if (i >= (rowcol * rows)) {
+        ++rowcol;
+        if (config.serpentine) {
+          y -= yinc;
+          yinc = -yinc;
+        } else {
+          y = ystart;
+        }
+        x += xinc;
+      }
+    }
+    if (values[i] > 0)
+      drawList->AddRectFilled(ImVec2(x, y), ImVec2(x + size, y + size),
+                              colors[values[i] - 1]);
+    else if (values[i] < 0)
+      drawList->AddRect(ImVec2(x, y), ImVec2(x + size, y + size),
+                        colors[-values[i] - 1], 0.0f, 0, 1.0);
+    if (sources) {
+      ImGui::SetCursorScreenPos(ImVec2(x - sized2, y - sized2));
+      if (sources[i]) {
+        ImGui::PushID(i);
+        ImGui::Selectable("", false, 0, ImVec2(inc, inc));
+        sources[i]->EmitDrag();
+        ImGui::PopID();
+      } else {
+        ImGui::Dummy(ImVec2(inc, inc));
+      }
+    }
+    if (config.order == LEDConfig::RowMajor) {
+      x += xinc;
+    } else {
+      y += yinc;
+    }
+  }
+
+  if (!sources) ImGui::Dummy(ImVec2(inc * cols, inc * rows));
+}
+
+void DrawLEDs(const int* values, int numValues, int cols, const ImU32* colors,
+              float size, float spacing, const LEDConfig& config) {
+  DrawLEDSources(values, nullptr, numValues, cols, colors, size, spacing,
+                 config);
+}
+
+bool DeleteButton(ImGuiID id, const ImVec2& pos) {
+  ImGuiContext& g = *GImGui;
+  ImGuiWindow* window = g.CurrentWindow;
+
+  // We intentionally allow interaction when clipped so that a mechanical
+  // Alt,Right,Validate sequence close a window. (this isn't the regular
+  // behavior of buttons, but it doesn't affect the user much because navigation
+  // tends to keep items visible).
+  const ImRect bb(
+      pos, pos + ImVec2(g.FontSize, g.FontSize) + g.Style.FramePadding * 2.0f);
+  bool is_clipped = !ImGui::ItemAdd(bb, id);
+
+  bool hovered, held;
+  bool pressed = ImGui::ButtonBehavior(bb, id, &hovered, &held);
+  if (is_clipped) return pressed;
+
+  // Render
+  ImU32 col =
+      ImGui::GetColorU32(held ? ImGuiCol_ButtonActive : ImGuiCol_ButtonHovered);
+  ImVec2 center = bb.GetCenter();
+  if (hovered)
+    window->DrawList->AddCircleFilled(
+        center, ImMax(2.0f, g.FontSize * 0.5f + 1.0f), col, 12);
+
+  ImU32 cross_col = ImGui::GetColorU32(ImGuiCol_Text);
+  window->DrawList->AddCircle(center, ImMax(2.0f, g.FontSize * 0.5f + 1.0f),
+                              cross_col, 12);
+  float cross_extent = g.FontSize * 0.5f * 0.5f - 1.0f;
+  center -= ImVec2(0.5f, 0.5f);
+  window->DrawList->AddLine(center + ImVec2(+cross_extent, +cross_extent),
+                            center + ImVec2(-cross_extent, -cross_extent),
+                            cross_col, 1.0f);
+  window->DrawList->AddLine(center + ImVec2(+cross_extent, -cross_extent),
+                            center + ImVec2(-cross_extent, +cross_extent),
+                            cross_col, 1.0f);
+
+  return pressed;
+}
+
+bool HeaderDeleteButton(const char* label) {
+  ImGuiWindow* window = ImGui::GetCurrentWindow();
+  ImGuiContext& g = *GImGui;
+  ImGuiItemHoveredDataBackup last_item_backup;
+  ImGuiID id = window->GetID(label);
+  float button_size = g.FontSize;
+  float button_x = ImMax(window->DC.LastItemRect.Min.x,
+                         window->DC.LastItemRect.Max.x -
+                             g.Style.FramePadding.x * 2.0f - button_size);
+  float button_y = window->DC.LastItemRect.Min.y;
+  bool rv = DeleteButton(
+      window->GetID(reinterpret_cast<void*>(static_cast<intptr_t>(id) + 1)),
+      ImVec2(button_x, button_y));
+  last_item_backup.Restore();
+  return rv;
+}
+
+}  // namespace glass