Displaying entities in different colors using DrawableOverrule

By Balaji Ramamoorthy

Recently, a developer wanted to know a method to display the entities in different colors to visually represent the results of a drawing comparison. A way to set the color for entities including those that are nested is explained in Kean’s blog post :

Changing the colour of nested AutoCAD entities through .NET
Another way to show the entity in different colors would be to use of DrawableOverrule. But, the WorldDraw of the DrawableOverrule class does not use the color setting from the DrawableTraits for some entities such as MText. To overcome this limitation, the drawable is cloned inside the WorldDraw method before being assigned a new color.

Here is a sample code using this approach. Some of the helper methods to highlight / unhighlight and pick nested entities are from Kean’s blog post that I mentioned about previously.
<p

using Autodesk.AutoCAD.GraphicsInterface;
using System.Collections.Generic;
 
public class MyDrawOverrule : DrawableOverrule
{
    public static List _redIds = new List();
    public static List _yellowIds = new List();
 
    public override bool WorldDraw(Drawable drawable, WorldDraw wd)
    {
        Entity mydrawable = drawable.Clone() as Entity;
 
        short colorIndex = 1;
        if (_yellowIds.Contains(drawable.Id))
            colorIndex = 2;
 
        wd.SubEntityTraits.Color = colorIndex;
        mydrawable.ColorIndex = colorIndex;
 
        return base.WorldDraw(mydrawable, wd);
    }
 
    public override int SetAttributes(Drawable drawable,
                                        DrawableTraits traits)
    {
        return base.SetAttributes(drawable, traits);
    }
}
 
public class ColorizeClass : IExtensionApplication
{
    static MyDrawOverrule _do = null;
 
    [CommandMethod("Colorize")]
    public void ColorizeMethod()
    {
        Document doc = Application.DocumentManager.MdiActiveDocument;
        Editor ed = doc.Editor;
 
        if (_do != null)
        {
            ed.WriteMessage("Overruling is already active");
            return;
        }
 
        Transaction tr = doc.TransactionManager.StartTransaction();
        using (tr)
        {
            List paths1;
            SelectNestedEntities(   ed, 
                                    out MyDrawOverrule._redIds, 
                                    out paths1, 
                                    "Red"
                                );
 
            List paths2;
            SelectNestedEntities(  ed, 
                                    out MyDrawOverrule._yellowIds, 
                                    out paths2, 
                                    "Yellow"
                                 );
 
            _do = new MyDrawOverrule();
 
            Overrule.AddOverrule(
                RXObject.GetClass(typeof(Entity)), 
                _do, 
                true);
 
            List ids = new List();
            ids.AddRange(MyDrawOverrule._redIds.ToArray());
            ids.AddRange(MyDrawOverrule._yellowIds.ToArray());
            _do.SetIdFilter(ids.ToArray());
 
            Overrule.Overruling = true;
 
            if (MyDrawOverrule._redIds.Count > 0)
                UnhighlightSubEntities(paths1);
 
            if (MyDrawOverrule._yellowIds.Count > 0)
                UnhighlightSubEntities(paths2);
 
            tr.Commit();
        }
 
        ed.Regen();
    }
 
    private static bool SelectNestedEntities
        (
            Editor ed, 
            out List ids, 
            out List paths, 
            String colorName
        )
    {
        ids = new List();
        paths = new List();
 
        // Loop until cancelled or completed
        PromptNestedEntityResult rs;
 
        do
        {
            rs = ed.GetNestedEntity(
                String.Format("nSelect entity to color {0}: ",
                colorName));
 
            if (rs.Status == PromptStatus.OK)
            {
                ids.Add(rs.ObjectId);
                FullSubentityPath path = FullSubentityPath.Null;
                path = HighlightSubEntity(rs);
                if (path != FullSubentityPath.Null)
                    paths.Add(path);
            }
        } while (rs.Status == PromptStatus.OK);
 
        return (rs.Status == PromptStatus.Cancel);
    }
 
    // Ask the user to select a number of sub-entities.
    // These will have their ObjectIds and their sub-entity
    // paths (returned from the HighlightSubEntity() helper)
    // added to collections that are returned to the caller.
    private static bool SelectNestedEntities
        (
            Editor ed, 
            out ObjectIdCollection ids, 
            out List paths
        )
    {
        ids = new ObjectIdCollection();
        paths = new List();
 
        // Loop until cancelled or completed
        PromptNestedEntityResult rs;
 
        do
        {
            rs = ed.GetNestedEntity("nSelect nested entity: ");
            if (rs.Status == PromptStatus.OK)
            {
                ids.Add(rs.ObjectId);
                FullSubentityPath path = FullSubentityPath.Null;
                path = HighlightSubEntity(rs);
                if (path != FullSubentityPath.Null)
                    paths.Add(path);
            }
        } while (rs.Status == PromptStatus.OK);
 
        // Cancel is the status when "enter" is used to
        // terminate the selection, which means we can't
        // use it to distinguish from an actual
        // cancellation.
        return (rs.Status == PromptStatus.Cancel);
    }
 
    // Unhighlight a set of sub-entities
    private static void UnhighlightSubEntities(
                                List paths)
    {
        for (int i = 0; i < paths.Count; i++)
        {
            ObjectId[] ids = paths[i].GetObjectIds();
            Entity ent 
                = ids[0].GetObject(OpenMode.ForRead) as Entity;
            if (ent != null)
            {
                ent.Unhighlight(paths[i], false);
            }
        }
    }
 
    // Highlight a sub-entity based on its nested
    // selection information.
    // Return the calculated sub-entity path, so
    // the calling application can later unhighlight.
    private static FullSubentityPath HighlightSubEntity(
                                    PromptNestedEntityResult rs)
    {
        // Extract relevant information from the prompt object
        ObjectId selId = rs.ObjectId;
        List objIds = new List(rs.GetContainers());
 
        // Reverse the "containers" list
        objIds.Reverse();
 
        // Now append the selected entity
        objIds.Add(selId);
 
        // Retrieve the sub-entity path for this entity
        SubentityId subEnt 
            = new SubentityId(SubentityType.Null, System.IntPtr.Zero);
 
        FullSubentityPath path 
            = new FullSubentityPath(objIds.ToArray(), subEnt);
 
        // Open the outermost container, relying on the open transaction...
        Entity ent = objIds[0].GetObject(OpenMode.ForRead) as Entity;
 
        // ... and highlight the nested entity
        if (ent == null)
            return FullSubentityPath.Null;
 
        ent.Highlight(path, false);
 
        // Return the sub-entity path for later unhighlighting
        return path;
    }
 
    void IExtensionApplication.Initialize() { }
 
    void IExtensionApplication.Terminate()
    {
        if (_do != null)
        {
            Overrule.Overruling = false;
            Overrule.RemoveOverrule(
                RXObject.GetClass(typeof(Entity)), 
                _do);
        }
    }
}