JAL-3551 concatenate colour by sequence commands for all except PyMOL
[jalview.git] / src / jalview / ext / rbvi / chimera / ChimeraCommands.java
index bb9df8a..c9dbc1d 100644 (file)
  */
 package jalview.ext.rbvi.chimera;
 
+import java.awt.Color;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+import jalview.api.AlignViewportI;
+import jalview.api.AlignmentViewPanel;
 import jalview.api.FeatureRenderer;
-import jalview.api.SequenceRenderer;
 import jalview.datamodel.AlignmentI;
+import jalview.datamodel.MappedFeatures;
 import jalview.datamodel.SequenceFeature;
 import jalview.datamodel.SequenceI;
+import jalview.gui.Desktop;
+import jalview.structure.AtomSpecModel;
+import jalview.structure.StructureCommand;
+import jalview.structure.StructureCommandI;
+import jalview.structure.StructureCommandsBase;
 import jalview.structure.StructureMapping;
-import jalview.structure.StructureMappingcommandSet;
 import jalview.structure.StructureSelectionManager;
 import jalview.util.ColorUtils;
-import jalview.util.Comparison;
-
-import java.awt.Color;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
 
 /**
  * Routines for generating Chimera commands for Jalview/Chimera binding
@@ -44,276 +50,61 @@ import java.util.Map;
  * @author JimP
  * 
  */
-public class ChimeraCommands
+public class ChimeraCommands extends StructureCommandsBase
 {
+  private static final StructureCommand SHOW_BACKBONE = new StructureCommand(
+          "~display all;~ribbon;chain @CA|P");
 
   public static final String NAMESPACE_PREFIX = "jv_";
 
-  /**
-   * Constructs Chimera commands to colour residues as per the Jalview alignment
-   * 
-   * @param ssm
-   * @param files
-   * @param sequence
-   * @param sr
-   * @param fr
-   * @param alignment
-   * @return
-   */
-  public static StructureMappingcommandSet[] getColourBySequenceCommand(
-          StructureSelectionManager ssm, String[] files,
-          SequenceI[][] sequence, SequenceRenderer sr, FeatureRenderer fr,
-          AlignmentI alignment)
-  {
-    Map<Object, AtomSpecModel> colourMap = buildColoursMap(ssm, files,
-            sequence, sr, fr, alignment);
+  private static final StructureCommandI COLOUR_BY_CHARGE = new StructureCommand(
+          "color white;color red ::ASP,GLU;color blue ::LYS,ARG;color yellow ::CYS");
 
-    List<String> colourCommands = buildColourCommands(colourMap);
+  private static final StructureCommandI COLOUR_BY_CHAIN = new StructureCommand(
+          "rainbow chain");
 
-    StructureMappingcommandSet cs = new StructureMappingcommandSet(
-            ChimeraCommands.class, null,
-            colourCommands.toArray(new String[colourCommands.size()]));
-
-    return new StructureMappingcommandSet[] { cs };
-  }
-
-  /**
-   * Traverse the map of colours/models/chains/positions to construct a list of
-   * 'color' commands (one per distinct colour used). The format of each command
-   * is
-   * 
-   * <pre>
-   * <blockquote> 
-   * color colorname #modelnumber:range.chain 
-   * e.g. color #00ff00 #0:2.B,4.B,9-12.B|#1:1.A,2-6.A,...
-   * </blockquote>
-   * </pre>
-   * 
-   * @param colourMap
-   * @return
-   */
-  protected static List<String> buildColourCommands(
-          Map<Object, AtomSpecModel> colourMap)
-  {
-    /*
-     * This version concatenates all commands into a single String (semi-colon
-     * delimited). If length limit issues arise, refactor to return one color
-     * command per colour.
-     */
-    List<String> commands = new ArrayList<String>();
-    StringBuilder sb = new StringBuilder(256);
-    boolean firstColour = true;
-    for (Object key : colourMap.keySet())
-    {
-      Color colour = (Color) key;
-      String colourCode = ColorUtils.toTkCode(colour);
-      if (!firstColour)
-      {
-        sb.append("; ");
-      }
-      sb.append("color ").append(colourCode).append(" ");
-      firstColour = false;
-      final AtomSpecModel colourData = colourMap.get(colour);
-      sb.append(colourData.getAtomSpec());
-    }
-    commands.add(sb.toString());
-    return commands;
-  }
-
-  /**
-   * Traverses a map of { modelNumber, {chain, {list of from-to ranges} } } and
-   * builds a Chimera format atom spec
-   * 
-   * @param modelAndChainRanges
-   */
-  protected static String getAtomSpec(
-          Map<Integer, Map<String, List<int[]>>> modelAndChainRanges)
-  {
-    StringBuilder sb = new StringBuilder(128);
-    boolean firstModelForColour = true;
-    for (Integer model : modelAndChainRanges.keySet())
-    {
-      boolean firstPositionForModel = true;
-      if (!firstModelForColour)
-      {
-        sb.append("|");
-      }
-      firstModelForColour = false;
-      sb.append("#").append(model).append(":");
-
-      final Map<String, List<int[]>> modelData = modelAndChainRanges
-              .get(model);
-      for (String chain : modelData.keySet())
-      {
-        boolean hasChain = !"".equals(chain.trim());
-        for (int[] range : modelData.get(chain))
-        {
-          if (!firstPositionForModel)
-          {
-            sb.append(",");
-          }
-          if (range[0] == range[1])
-          {
-            sb.append(range[0]);
-          }
-          else
-          {
-            sb.append(range[0]).append("-").append(range[1]);
-          }
-          if (hasChain)
-          {
-            sb.append(".").append(chain);
-          }
-          firstPositionForModel = false;
-        }
-      }
-    }
-    return sb.toString();
-  }
+  // Chimera clause to exclude alternate locations in atom selection
+  private static final String NO_ALTLOCS = "&~@.B-Z&~@.2-9";
 
-  /**
-   * <pre>
-   * Build a data structure which maps contiguous subsequences for each colour. 
-   * This generates a data structure from which we can easily generate the 
-   * Chimera command for colour by sequence.
-   * Color
-   *     Model number
-   *         Chain
-   *             list of start/end ranges
-   * Ordering is by order of addition (for colours and positions), natural ordering (for models and chains)
-   * </pre>
-   */
-  protected static Map<Object, AtomSpecModel> buildColoursMap(
-          StructureSelectionManager ssm, String[] files,
-          SequenceI[][] sequence, SequenceRenderer sr, FeatureRenderer fr,
-          AlignmentI alignment)
+  @Override
+  public StructureCommandI getColourCommand(String atomSpec, Color colour)
   {
-    Map<Object, AtomSpecModel> colourMap = new LinkedHashMap<Object, AtomSpecModel>();
-    Color lastColour = null;
-    for (int pdbfnum = 0; pdbfnum < files.length; pdbfnum++)
-    {
-      StructureMapping[] mapping = ssm.getMapping(files[pdbfnum]);
-
-      if (mapping == null || mapping.length < 1)
-      {
-        continue;
-      }
-
-      int startPos = -1, lastPos = -1;
-      String lastChain = "";
-      for (int s = 0; s < sequence[pdbfnum].length; s++)
-      {
-        for (int sp, m = 0; m < mapping.length; m++)
-        {
-          final SequenceI seq = sequence[pdbfnum][s];
-          if (mapping[m].getSequence() == seq
-                  && (sp = alignment.findIndex(seq)) > -1)
-          {
-            SequenceI asp = alignment.getSequenceAt(sp);
-            for (int r = 0; r < asp.getLength(); r++)
-            {
-              // no mapping to gaps in sequence
-              if (Comparison.isGap(asp.getCharAt(r)))
-              {
-                continue;
-              }
-              int pos = mapping[m].getPDBResNum(asp.findPosition(r));
-
-              if (pos < 1 || pos == lastPos)
-              {
-                continue;
-              }
-
-              Color colour = sr.getResidueColour(seq, r, fr);
-              final String chain = mapping[m].getChain();
-
-              /*
-               * Just keep incrementing the end position for this colour range
-               * _unless_ colour, PDB model or chain has changed, or there is a
-               * gap in the mapped residue sequence
-               */
-              final boolean newColour = !colour.equals(lastColour);
-              final boolean nonContig = lastPos + 1 != pos;
-              final boolean newChain = !chain.equals(lastChain);
-              if (newColour || nonContig || newChain)
-              {
-                if (startPos != -1)
-                {
-                  addColourRange(colourMap, lastColour, pdbfnum, startPos,
-                          lastPos, lastChain);
-                }
-                startPos = pos;
-              }
-              lastColour = colour;
-              lastPos = pos;
-              lastChain = chain;
-            }
-            // final colour range
-            if (lastColour != null)
-            {
-              addColourRange(colourMap, lastColour, pdbfnum, startPos, lastPos,
-                      lastChain);
-            }
-            // break;
-          }
-        }
-      }
-    }
-    return colourMap;
+    // https://www.cgl.ucsf.edu/chimera/current/docs/UsersGuide/midas/color.html
+    String colourCode = getColourString(colour);
+    return new StructureCommand("color " + colourCode + " " + atomSpec);
   }
 
   /**
-   * Helper method to add one contiguous colour range to the colour map.
+   * Returns a colour formatted suitable for use in viewer command syntax
    * 
-   * @param map
-   * @param key
-   * @param model
-   * @param startPos
-   * @param endPos
-   * @param chain
+   * @param colour
+   * @return
    */
-  protected static void addColourRange(Map<Object, AtomSpecModel> map,
-          Object key, int model, int startPos, int endPos, String chain)
+  protected String getColourString(Color colour)
   {
-    /*
-     * Get/initialize map of data for the colour
-     */
-    AtomSpecModel atomSpec = map.get(key);
-    if (atomSpec == null)
-    {
-      atomSpec = new AtomSpecModel();
-      map.put(key, atomSpec);
-    }
-
-    atomSpec.addRange(model, startPos, endPos, chain);
+    return ColorUtils.toTkCode(colour);
   }
 
   /**
    * Constructs and returns Chimera commands to set attributes on residues
-   * corresponding to features in Jalview. Attribute names are the Jalview
-   * feature type, with a "jv_" prefix.
+   * corresponding to features in Jalview. Attribute names are the Jalview feature
+   * type, with a "jv_" prefix.
    * 
    * @param ssm
    * @param files
    * @param seqs
-   * @param fr
-   * @param alignment
+   * @param viewPanel
    * @return
    */
-  public static StructureMappingcommandSet getSetAttributeCommandsForFeatures(
-          StructureSelectionManager ssm, String[] files,
-          SequenceI[][] seqs, FeatureRenderer fr, AlignmentI alignment)
+  @Override
+  public List<StructureCommandI> setAttributesForFeatures(
+          StructureSelectionManager ssm, String[] files, SequenceI[][] seqs,
+          AlignmentViewPanel viewPanel)
   {
     Map<String, Map<Object, AtomSpecModel>> featureMap = buildFeaturesMap(
-            ssm, files, seqs, fr, alignment);
-
-    List<String> commands = buildSetAttributeCommands(featureMap);
-
-    StructureMappingcommandSet cs = new StructureMappingcommandSet(
-            ChimeraCommands.class, null,
-            commands.toArray(new String[commands.size()]));
+            ssm, files, seqs, viewPanel);
 
-    return cs;
+    return setAttributes(featureMap);
   }
 
   /**
@@ -325,24 +116,51 @@ public class ChimeraCommands
    * @param ssm
    * @param files
    * @param seqs
-   * @param fr
-   * @param alignment
+   * @param viewPanel
    * @return
    */
-  protected static Map<String, Map<Object, AtomSpecModel>> buildFeaturesMap(
-          StructureSelectionManager ssm, String[] files,
-          SequenceI[][] seqs, FeatureRenderer fr, AlignmentI alignment)
+  protected Map<String, Map<Object, AtomSpecModel>> buildFeaturesMap(
+          StructureSelectionManager ssm, String[] files, SequenceI[][] seqs,
+          AlignmentViewPanel viewPanel)
   {
-    Map<String, Map<Object, AtomSpecModel>> theMap = new LinkedHashMap<String, Map<Object, AtomSpecModel>>();
+    Map<String, Map<Object, AtomSpecModel>> theMap = new LinkedHashMap<>();
 
+    FeatureRenderer fr = viewPanel.getFeatureRenderer();
+    if (fr == null)
+    {
+      return theMap;
+    }
+
+    AlignViewportI viewport = viewPanel.getAlignViewport();
     List<String> visibleFeatures = fr.getDisplayedFeatureTypes();
-    if (visibleFeatures.isEmpty())
+
+    /*
+     * if alignment is showing features from complement, we also transfer
+     * these features to the corresponding mapped structure residues
+     */
+    boolean showLinkedFeatures = viewport.isShowComplementFeatures();
+    List<String> complementFeatures = new ArrayList<>();
+    FeatureRenderer complementRenderer = null;
+    if (showLinkedFeatures)
+    {
+      AlignViewportI comp = fr.getViewport().getCodingComplement();
+      if (comp != null)
+      {
+        complementRenderer = Desktop.getAlignFrameFor(comp)
+                .getFeatureRenderer();
+        complementFeatures = complementRenderer.getDisplayedFeatureTypes();
+      }
+    }
+    if (visibleFeatures.isEmpty() && complementFeatures.isEmpty())
     {
       return theMap;
     }
 
+    AlignmentI alignment = viewPanel.getAlignment();
     for (int pdbfnum = 0; pdbfnum < files.length; pdbfnum++)
     {
+      final int modelNumber = pdbfnum + getModelStartNo();
+      String modelId = String.valueOf(modelNumber);
       StructureMapping[] mapping = ssm.getMapping(files[pdbfnum]);
 
       if (mapping == null || mapping.length < 1)
@@ -356,16 +174,23 @@ public class ChimeraCommands
         {
           final SequenceI seq = seqs[pdbfnum][seqNo];
           int sp = alignment.findIndex(seq);
-          if (mapping[m].getSequence() == seq && sp > -1)
+          StructureMapping structureMapping = mapping[m];
+          if (structureMapping.getSequence() == seq && sp > -1)
           {
             /*
              * found a sequence with a mapping to a structure;
              * now scan its features
              */
-            SequenceI asp = alignment.getSequenceAt(sp);
-
-            scanSequenceFeatures(visibleFeatures, mapping[m], asp, theMap,
-                    pdbfnum);
+            if (!visibleFeatures.isEmpty())
+            {
+              scanSequenceFeatures(visibleFeatures, structureMapping, seq,
+                      theMap, modelId);
+            }
+            if (showLinkedFeatures)
+            {
+              scanComplementFeatures(complementRenderer, structureMapping,
+                      seq, theMap, modelId);
+            }
           }
         }
       }
@@ -374,40 +199,112 @@ public class ChimeraCommands
   }
 
   /**
+   * Scans visible features in mapped positions of the CDS/peptide complement, and
+   * adds any found to the map of attribute values/structure positions
+   * 
+   * @param complementRenderer
+   * @param structureMapping
+   * @param seq
+   * @param theMap
+   * @param modelNumber
+   */
+  protected static void scanComplementFeatures(
+          FeatureRenderer complementRenderer,
+          StructureMapping structureMapping, SequenceI seq,
+          Map<String, Map<Object, AtomSpecModel>> theMap,
+          String modelNumber)
+  {
+    /*
+     * for each sequence residue mapped to a structure position...
+     */
+    for (int seqPos : structureMapping.getMapping().keySet())
+    {
+      /*
+       * find visible complementary features at mapped position(s)
+       */
+      MappedFeatures mf = complementRenderer
+              .findComplementFeaturesAtResidue(seq, seqPos);
+      if (mf != null)
+      {
+        for (SequenceFeature sf : mf.features)
+        {
+          String type = sf.getType();
+
+          /*
+           * Don't copy features which originated from Chimera
+           */
+          if (JalviewChimeraBinding.CHIMERA_FEATURE_GROUP
+                  .equals(sf.getFeatureGroup()))
+          {
+            continue;
+          }
+
+          /*
+           * record feature 'value' (score/description/type) as at the
+           * corresponding structure position
+           */
+          List<int[]> mappedRanges = structureMapping
+                  .getPDBResNumRanges(seqPos, seqPos);
+
+          if (!mappedRanges.isEmpty())
+          {
+            String value = sf.getDescription();
+            if (value == null || value.length() == 0)
+            {
+              value = type;
+            }
+            float score = sf.getScore();
+            if (score != 0f && !Float.isNaN(score))
+            {
+              value = Float.toString(score);
+            }
+            Map<Object, AtomSpecModel> featureValues = theMap.get(type);
+            if (featureValues == null)
+            {
+              featureValues = new HashMap<>();
+              theMap.put(type, featureValues);
+            }
+            for (int[] range : mappedRanges)
+            {
+              addAtomSpecRange(featureValues, value, modelNumber, range[0],
+                      range[1], structureMapping.getChain());
+            }
+          }
+        }
+      }
+    }
+  }
+
+  /**
    * Inspect features on the sequence; for each feature that is visible,
    * determine its mapped ranges in the structure (if any) according to the
-   * given mapping, and add them to the map
+   * given mapping, and add them to the map.
    * 
    * @param visibleFeatures
    * @param mapping
    * @param seq
    * @param theMap
-   * @param modelNumber
+   * @param modelId
    */
   protected static void scanSequenceFeatures(List<String> visibleFeatures,
           StructureMapping mapping, SequenceI seq,
-          Map<String, Map<Object, AtomSpecModel>> theMap, int modelNumber)
+          Map<String, Map<Object, AtomSpecModel>> theMap, String modelId)
   {
-    SequenceFeature[] sfs = seq.getSequenceFeatures();
-    if (sfs == null)
-    {
-      return;
-    }
-
+    List<SequenceFeature> sfs = seq.getFeatures().getPositionalFeatures(
+            visibleFeatures.toArray(new String[visibleFeatures.size()]));
     for (SequenceFeature sf : sfs)
     {
       String type = sf.getType();
 
       /*
-       * Only copy visible features, don't copy any which originated
-       * from Chimera, and suppress uninteresting ones (e.g. RESNUM)
+       * Don't copy features which originated from Chimera
        */
-      boolean isFromViewer = JalviewChimeraBinding.CHIMERA_FEATURE_GROUP
-              .equals(sf.getFeatureGroup());
-      if (isFromViewer || !visibleFeatures.contains(type))
+      if (JalviewChimeraBinding.CHIMERA_FEATURE_GROUP
+              .equals(sf.getFeatureGroup()))
       {
         continue;
       }
+
       List<int[]> mappedRanges = mapping.getPDBResNumRanges(sf.getBegin(),
               sf.getEnd());
 
@@ -426,13 +323,13 @@ public class ChimeraCommands
         Map<Object, AtomSpecModel> featureValues = theMap.get(type);
         if (featureValues == null)
         {
-          featureValues = new HashMap<Object, AtomSpecModel>();
+          featureValues = new HashMap<>();
           theMap.put(type, featureValues);
         }
         for (int[] range : mappedRanges)
         {
-          addColourRange(featureValues, value, modelNumber, range[0], range[1],
-                  mapping.getChain());
+          addAtomSpecRange(featureValues, value, modelId, range[0],
+                  range[1], mapping.getChain());
         }
       }
     }
@@ -446,17 +343,17 @@ public class ChimeraCommands
    * 
    * <pre>
    * <blockquote> setattr r <featureName> " " #modelnumber:range.chain 
-   * e.g. setattr r jv:chain <value> #0:2.B,4.B,9-12.B|#1:1.A,2-6.A,...
+   * e.g. setattr r jv_chain &lt;value&gt; #0:2.B,4.B,9-12.B|#1:1.A,2-6.A,...
    * </blockquote>
    * </pre>
    * 
    * @param featureMap
    * @return
    */
-  protected static List<String> buildSetAttributeCommands(
+  protected List<StructureCommandI> setAttributes(
           Map<String, Map<Object, AtomSpecModel>> featureMap)
   {
-    List<String> commands = new ArrayList<String>();
+    List<StructureCommandI> commands = new ArrayList<>();
     for (String featureType : featureMap.keySet())
     {
       String attributeName = makeAttributeName(featureType);
@@ -475,13 +372,12 @@ public class ChimeraCommands
          * add a command to set the attribute on the mapped residues
          * Put values in single quotes, encoding any embedded single quotes
          */
-        StringBuilder sb = new StringBuilder(128);
+        AtomSpecModel atomSpecModel = values.get(value);
         String featureValue = value.toString();
-        featureValue.replaceAll("'", "&#39;");
-        sb.append("setattr r ").append(attributeName).append(" '")
-                .append(featureValue).append("' ");
-        sb.append(values.get(value).getAtomSpec());
-        commands.add(sb.toString());
+        featureValue = featureValue.replaceAll("\\'", "&#39;");
+        StructureCommandI cmd = setAttribute(attributeName, featureValue,
+                atomSpecModel);
+        commands.add(cmd);
       }
     }
 
@@ -489,14 +385,37 @@ public class ChimeraCommands
   }
 
   /**
+   * Returns a viewer command to set the given residue attribute value on
+   * residues specified by the AtomSpecModel, for example
+   * 
+   * <pre>
+   * setatr res jv_chain 'primary' #1:12-34,48-55.B
+   * </pre>
+   * 
+   * @param attributeName
+   * @param attributeValue
+   * @param atomSpecModel
+   * @return
+   */
+  protected StructureCommandI setAttribute(String attributeName,
+          String attributeValue,
+          AtomSpecModel atomSpecModel)
+  {
+    StringBuilder sb = new StringBuilder(128);
+    sb.append("setattr res ").append(attributeName).append(" '")
+            .append(attributeValue).append("' ");
+    sb.append(getAtomSpec(atomSpecModel, false));
+    return new StructureCommand(sb.toString());
+  }
+
+  /**
    * Makes a prefixed and valid Chimera attribute name. A jv_ prefix is applied
    * for a 'Jalview' namespace, and any non-alphanumeric character is converted
    * to an underscore.
    * 
    * @param featureType
-   * @return <pre>
+   * @return
    * @see https://www.cgl.ucsf.edu/chimera/current/docs/UsersGuide/midas/setattr.html
-   * </pre>
    */
   protected static String makeAttributeName(String featureType)
   {
@@ -522,4 +441,231 @@ public class ChimeraCommands
     return attName;
   }
 
+  @Override
+  public StructureCommandI colourByChain()
+  {
+    return COLOUR_BY_CHAIN;
+  }
+
+  @Override
+  public List<StructureCommandI> colourByCharge()
+  {
+    return Arrays.asList(COLOUR_BY_CHARGE);
+  }
+
+  @Override
+  public String getResidueSpec(String residue)
+  {
+    return "::" + residue;
+  }
+
+  @Override
+  public StructureCommandI setBackgroundColour(Color col)
+  {
+    // https://www.cgl.ucsf.edu/chimera/current/docs/UsersGuide/midas/set.html#bgcolor
+    return new StructureCommand("set bgColor " + ColorUtils.toTkCode(col));
+  }
+
+  @Override
+  public StructureCommandI focusView()
+  {
+    // https://www.cgl.ucsf.edu/chimera/current/docs/UsersGuide/midas/focus.html
+    return new StructureCommand("focus");
+  }
+
+  @Override
+  public List<StructureCommandI> showChains(List<String> toShow)
+  {
+    /*
+     * Construct a chimera command like
+     * 
+     * ~display #*;~ribbon #*;ribbon :.A,:.B
+     */
+    StringBuilder cmd = new StringBuilder(64);
+    boolean first = true;
+    for (String chain : toShow)
+    {
+      String[] tokens = chain.split(":");
+      if (tokens.length == 2)
+      {
+        String showChainCmd = tokens[0] + ":." + tokens[1];
+        if (!first)
+        {
+          cmd.append(",");
+        }
+        cmd.append(showChainCmd);
+        first = false;
+      }
+    }
+
+    /*
+     * could append ";focus" to this command to resize the display to fill the
+     * window, but it looks more helpful not to (easier to relate chains to the
+     * whole)
+     */
+    final String command = "~display #*; ~ribbon #*; ribbon :"
+            + cmd.toString();
+    return Arrays.asList(new StructureCommand(command));
+  }
+
+  @Override
+  public List<StructureCommandI> superposeStructures(AtomSpecModel ref,
+          AtomSpecModel spec)
+  {
+    /*
+     * Form Chimera match command to match spec to ref
+     * (the first set of atoms are moved on to the second)
+     * 
+     * match #1:1-30.B,81-100.B@CA #0:21-40.A,61-90.A@CA
+     * 
+     * @see https://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/match.html
+     */
+    StringBuilder cmd = new StringBuilder();
+    String atomSpecAlphaOnly = getAtomSpec(spec, true);
+    String refSpecAlphaOnly = getAtomSpec(ref, true);
+    cmd.append("match ").append(atomSpecAlphaOnly).append(" ").append(refSpecAlphaOnly);
+
+    /*
+     * show superposed residues as ribbon
+     */
+    String atomSpec = getAtomSpec(spec, false);
+    String refSpec = getAtomSpec(ref, false);
+    cmd.append("; ribbon ");
+    cmd.append(atomSpec).append("|").append(refSpec).append("; focus");
+
+    return Arrays.asList(new StructureCommand(cmd.toString()));
+  }
+
+  @Override
+  public StructureCommandI openCommandFile(String path)
+  {
+    // https://www.cgl.ucsf.edu/chimera/current/docs/UsersGuide/filetypes.html
+    return new StructureCommand("open cmd:" + path);
+  }
+
+  @Override
+  public StructureCommandI saveSession(String filepath)
+  {
+    // https://www.cgl.ucsf.edu/chimera/current/docs/UsersGuide/midas/save.html
+    return new StructureCommand("save " + filepath);
+  }
+
+  /**
+   * Returns the range(s) modelled by {@code atomSpec} formatted as a Chimera
+   * atomspec string, e.g.
+   * 
+   * <pre>
+   * #0:15.A,28.A,54.A,70-72.A|#1:2.A,6.A,11.A,13-14.A
+   * </pre>
+   * 
+   * where
+   * <ul>
+   * <li>#0 is a model number</li>
+   * <li>15 or 70-72 is a residue number, or range of residue numbers</li>
+   * <li>.A is a chain identifier</li>
+   * <li>residue ranges are separated by comma</li>
+   * <li>atomspecs for distinct models are separated by | (or)</li>
+   * </ul>
+   * 
+   * <pre>
+   * 
+   * @param model
+   * @param alphaOnly
+   * @return
+   * @see https://www.cgl.ucsf.edu/chimera/current/docs/UsersGuide/midas/frameatom_spec.html
+   */
+  @Override
+  public String getAtomSpec(AtomSpecModel atomSpec, boolean alphaOnly)
+  {
+    StringBuilder sb = new StringBuilder(128);
+    boolean firstModel = true;
+    for (String model : atomSpec.getModels())
+    {
+      if (!firstModel)
+      {
+        sb.append("|");
+      }
+      firstModel = false;
+      appendModel(sb, model, atomSpec, alphaOnly);
+    }
+    return sb.toString();
+  }
+
+  /**
+   * A helper method to append an atomSpec string for atoms in the given model
+   * 
+   * @param sb
+   * @param model
+   * @param atomSpec
+   * @param alphaOnly
+   */
+  protected void appendModel(StringBuilder sb, String model,
+          AtomSpecModel atomSpec, boolean alphaOnly)
+  {
+    sb.append("#").append(model).append(":");
+
+    boolean firstPositionForModel = true;
+
+    for (String chain : atomSpec.getChains(model))
+    {
+      chain = " ".equals(chain) ? chain : chain.trim();
+
+      List<int[]> rangeList = atomSpec.getRanges(model, chain);
+      for (int[] range : rangeList)
+      {
+        appendRange(sb, range[0], range[1], chain, firstPositionForModel,
+                false);
+        firstPositionForModel = false;
+      }
+    }
+    if (alphaOnly)
+    {
+      /*
+       * restrict to alpha carbon, no alternative locations
+       * (needed to ensuring matching atom counts for superposition)
+       */
+      // TODO @P instead if RNA - add nucleotide flag to AtomSpecModel?
+      sb.append("@CA").append(NO_ALTLOCS);
+    }
+  }
+
+  @Override
+  public List<StructureCommandI> showBackbone()
+  {
+    return Arrays.asList(SHOW_BACKBONE);
+  }
+
+  @Override
+  public StructureCommandI loadFile(String file)
+  {
+    return new StructureCommand("open " + file);
+  }
+
+  /**
+   * Overrides the default method to concatenate colour commands into one
+   */
+  @Override
+  public List<StructureCommandI> colourBySequence(
+          Map<Object, AtomSpecModel> colourMap)
+  {
+    List<StructureCommandI> commands = new ArrayList<>();
+    StringBuilder sb = new StringBuilder(colourMap.size() * 20);
+    boolean first = true;
+    for (Object key : colourMap.keySet())
+    {
+      Color colour = (Color) key;
+      final AtomSpecModel colourData = colourMap.get(colour);
+      StructureCommandI command = getColourCommand(colourData, colour);
+      if (!first)
+      {
+        sb.append(getCommandSeparator());
+      }
+      first = false;
+      sb.append(command.getCommand());
+    }
+
+    commands.add(new StructureCommand(sb.toString()));
+    return commands;
+  }
+
 }