Retrieve Extended-Data properties, fallback to Dimension-Style properties.

[mme1950]

Standard properties of a Dimension... entity are specified by the associated DimensionStyle object. The standard values may be overridden by the entity's extended data.

A mechanism to retrieve effective property values, i.e. values from the extended data, if specified, defaulting to the properties of the DimensionStyle, is to be implemented.

Entity's Extended Data Overriding DimensionStyle Properties

Extended data for an etitiy appear as ExtendedDataDictionary. Entries of type ExtendedData refer to an AppId"/>. An ExtendedData entry contains a list of ExtendedDataRecord records. An ExtendedDataRecord contains a Code and a Value. The Code specifies the the data type of the value. An ExtendedDataRecord does not contain any information about purpose of the value.

The ExtendedData may have different structures. ExtendedData of Dimension and Leaderentities contain entries that are organized as follows:

• The first record contains the name of DSTYLE indicating that the values of the ExtendedData provide property values to override values of the DimensionStyle object.
  • We found out that the preceding record contains a group code defining the meaning of the value of this record. The group code matches the group code of the property to be overridden.

Example: When in AutoCAD for a LEADER a custom arrowsize is set, the value appears in an ExtendedData entry associated with the AppId key having the name ACAD. If an entry with the "type" record containing DSTYLE is found and a record with the group code 41 appears the following record contains the arrow-size value.

[mme1950]

Concept

• Namespace AcadSVG.Extensions
• class DimensionProperties
• Exposes all relevant properties of DimensionStyle
• Trys to read property value from extended data, if present, defaults to property value from the associated DimensionStyle object.
• Base class EntityProperties provides Methods to read extended data.

[mme1950]

Special Treatment of Object References

• If a record contains a handle, the respective CadObject is resolved.

Special Treatment of Index-Color and True-Color Values

• Index colors are represented by a short value and are converted into a Color object.
• If a true color is specified the color value appears in a separate ExtendedData entry with the name DSTYLE_TC under the same group code. When reading color values from extended data it is tried first to read a true-color value, then an indexed-color value, then defaults to the value from the DimensionStyle object.
• True-color values are coded as 24-byte chunk. The color is found in byte 10 (red), 9 (green), 8 (blue). Other bytes are ignored.