Add a preset enum to ColorTable

You can still select presets through strings (and we leave ourselves
open to add more presets through strings than enumerating with the
enum), but this provides a way to select a preset that is verified by
the compiler.

vtkm/cont/ColorTable.cxx

@@ -31,10 +31,26 @@ namespace cont
 
 namespace detail
 {
+bool loadColorTablePreset(vtkm::cont::ColorTable::Preset preset, vtkm::cont::ColorTable& table);
 std::set<std::string> GetPresetNames();
 bool loadColorTablePreset(std::string name, vtkm::cont::ColorTable& table);
 }
 
+//----------------------------------------------------------------------------
+ColorTable::ColorTable(vtkm::cont::ColorTable::Preset preset)
+  : Impl(std::make_shared<detail::ColorTableInternals>())
+{
+  const bool loaded = this->LoadPreset(preset);
+  if (!loaded)
+  { //if we failed to load the requested color table, call SetColorSpace
+    //so that the internal host side cache is constructed and we leave
+    //the constructor in a valid state. We use RGB as it is the default
+    //when the no parameter constructor is called
+    this->SetColorSpace(ColorSpace::LAB);
+  }
+  this->AddSegmentAlpha(this->Impl->TableRange.Min, 1.0f, this->Impl->TableRange.Max, 1.0f);
+}
+
 //----------------------------------------------------------------------------
 ColorTable::ColorTable(const std::string& name)
   : Impl(std::make_shared<detail::ColorTableInternals>())
@@ -88,6 +104,12 @@ ColorTable::~ColorTable()
 {
 }
 
+//----------------------------------------------------------------------------
+bool ColorTable::LoadPreset(vtkm::cont::ColorTable::Preset preset)
+{
+  return detail::loadColorTablePreset(preset, *this);
+}
+
 //----------------------------------------------------------------------------
 std::set<std::string> ColorTable::GetPresets() const
 {

vtkm/cont/ColorTable.h

@@ -108,6 +108,35 @@ class VTKM_CONT_EXPORT ColorTable
   std::shared_ptr<detail::ColorTableInternals> Impl;
 
 public:
+  // Note: these are in flux and will change soon.
+  enum struct Preset
+  {
+    DEFAULT,
+    COOL_TO_WARM,
+    BLACK_BODY_RADIATION,
+    SAMSEL_FIRE,
+    INFERNO,
+    LINEAR_YGB,
+    COLD_AND_HOT,
+    RAINBOW_DESATURATED,
+    COOL_TO_WARN_EXTENDED,
+    X_RAY,
+    BLACK_BLUE_AND_WHITE,
+    VIRDIS,
+    LINEAR_GREEN,
+    JET,
+    RAINBOW
+  };
+
+  /// \brief Construct a color table from a preset
+  ///
+  /// Constructs a color table from a given preset, which might include a NaN color.
+  /// The alpha table will have 2 entries of alpha = 1.0 with linear interpolation
+  ///
+  /// Note: these are a select set of the presets you can get by providing a string identifier.
+  ///
+  ColorTable(vtkm::cont::ColorTable::Preset preset);
+
   /// \brief Construct a color table from a preset color table
   ///
   /// Constructs a color table from a given preset, which might include a NaN color.
@@ -166,8 +195,13 @@ public:
 
   ~ColorTable();
 
+  bool LoadPreset(vtkm::cont::ColorTable::Preset preset);
+
   /// Returns the name of all preset color tables
   ///
+  /// This list will include all presets defined in vtkm::cont::ColorTable::Preset and could
+  /// include extras as well.
+  ///
   std::set<std::string> GetPresets() const;
 
   /// Load a preset color table

vtkm/cont/PresetColorTables.cxx

@@ -548,26 +548,34 @@ struct LoadColorTablePresetCommand
 {
   using FunctionType = void (*)(vtkm::cont::ColorTable& table);
 
+  vtkm::cont::ColorTable::Preset id;
   std::string name;
   FunctionType function;
 };
 
-constexpr int numberOfPresets = 14;
+constexpr int numberOfPresets = 15;
 struct LoadColorTablePresetCommand presets[numberOfPresets] = {
-  { "cool to warm", loadCoolToWarm },
-  { "black-body radiation", loadBlackBody },
-  { "samsel fire", loadSamselFire },
-  { "inferno", loadInferno },
-  { "linear ygb", loadLinearYGB },
-  { "cold and hot", loadColdAndHot },
-  { "rainbow desaturated", loadRainbowDesaturated },
-  { "cool to warm (extended)", loadCoolToWarmExtended },
-  { "x ray", loadXRay },
-  { "black, blue and white", loadBlackBlueWhite },
-  { "virdis", loadVirdis },
-  { "linear green", loadLinearGreen },
-  { "jet", loadJet },
-  { "rainbow", loadRainbow },
+  { vtkm::cont::ColorTable::Preset::DEFAULT, "default", loadCoolToWarm },
+  { vtkm::cont::ColorTable::Preset::COOL_TO_WARM, "cool to warm", loadCoolToWarm },
+  { vtkm::cont::ColorTable::Preset::BLACK_BODY_RADIATION, "black-body radiation", loadBlackBody },
+  { vtkm::cont::ColorTable::Preset::SAMSEL_FIRE, "samsel fire", loadSamselFire },
+  { vtkm::cont::ColorTable::Preset::INFERNO, "inferno", loadInferno },
+  { vtkm::cont::ColorTable::Preset::LINEAR_YGB, "linear ygb", loadLinearYGB },
+  { vtkm::cont::ColorTable::Preset::COLD_AND_HOT, "cold and hot", loadColdAndHot },
+  { vtkm::cont::ColorTable::Preset::RAINBOW_DESATURATED,
+    "rainbow desaturated",
+    loadRainbowDesaturated },
+  { vtkm::cont::ColorTable::Preset::COOL_TO_WARN_EXTENDED,
+    "cool to warm (extended)",
+    loadCoolToWarmExtended },
+  { vtkm::cont::ColorTable::Preset::X_RAY, "x ray", loadXRay },
+  { vtkm::cont::ColorTable::Preset::BLACK_BLUE_AND_WHITE,
+    "black, blue and white",
+    loadBlackBlueWhite },
+  { vtkm::cont::ColorTable::Preset::VIRDIS, "virdis", loadVirdis },
+  { vtkm::cont::ColorTable::Preset::LINEAR_GREEN, "linear green", loadLinearGreen },
+  { vtkm::cont::ColorTable::Preset::JET, "jet", loadJet },
+  { vtkm::cont::ColorTable::Preset::RAINBOW, "rainbow", loadRainbow },
 };
 }
 
@@ -577,6 +585,21 @@ namespace cont
 {
 namespace detail
 {
+
+VTKM_CONT_EXPORT
+bool loadColorTablePreset(vtkm::cont::ColorTable::Preset preset, vtkm::cont::ColorTable& table)
+{
+  for (int i = 0; i < numberOfPresets; ++i)
+  {
+    if (preset == presets[i].id)
+    {
+      presets[i].function(table);
+      return true;
+    }
+  }
+  return false;
+}
+
 VTKM_CONT_EXPORT std::set<std::string> GetPresetNames()
 {
   std::set<std::string> names;

vtkm/filter/testing/UnitTestFieldToColors.cxx

@@ -33,7 +33,7 @@ void TestFieldToColors()
   //build a color table with clamping off and verify that sampling works
   vtkm::Range range{ 0.0, 50.0 };
   vtkm::cont::ColorTable table;
-  table.LoadPreset("Cool to Warm");
+  table.LoadPreset(vtkm::cont::ColorTable::Preset::COOL_TO_WARM);
   table.RescaleToRange(range);
   table.SetClampingOff();
   table.SetAboveRangeColor(vtkm::Vec<float, 3>{ 1.0f, 0.0f, 0.0f }); //red