We are extremely pleased to announce the release of the 2nd Edition of the GDL Handbook.

Since publishing the first edition of the GDL Handbook back in 2009, things have moved on.  New GDL commands have been introduced, some old work-arounds have been rendered obsolete, and my own programming skills have matured. However most of the content of the first edition remains valid. The reason for this longevity is that the GDL Handbook was always designed to stand the test of time, by focussing on core aspects of GDL programming, namely program structure and design, problem-solving, geometry, and standard solutions to common problems.

In this second edition, much of the original content has remained intact, with minor adjustments as necessary to reflect some of the changes that have taken place in the past three versions of ArchiCAD.

I have taken the opportunity to re-format the page layout to make it easier to see at a glance which chapter and section you are currently reading. All images now include captions that serve a dual role as references within the main text, and as supplementary comments. I’ve also tried to make the text generally more readable, smoothing out some of the rougher and more cryptic passages, and using a larger type.

Some of the original sample scripts included typographical errors. In most cases these were either trivial (e.g. an error in a comment of the script) or else clearly wrong. Wherever such errors have been detected, they have been corrected in this edition. The section in on Smarter Font Selection originally included in chapter 13 Text has been removed, as it relied on being able to read and write data to the ArchiCAD Data Folder. This can still be done, but since the advent of Windows 7 writing to files in the Programs folder has become problematic for the majority of end-users.

Please note three particularly important changes to the second edition.

The first major change is the method of responding to button click events and parameter changes in the Parameters script. In the first edition, I recommended clearing the values of glob_modpar_name and glob_UI_button_ID at the foot of the script. This approach is no longer possible, due to a change introduced in ArchiCAD 13. A new solution has been provided by Graphisoft, and this is given on page 198.

The second change is a quite serious bug that I found in the sub-routine for finding the intersection of two line segments. This bug has been corrected on pages 281 – 282.

And last but not least, many of you will be pleased to know that an electronic version of the GDL Handbook is now available from the Cadimage World website www.cadimageworld.com.

Changes to the Format:

• Wider pages – the book sits open better
• All images are referenced in the text
• All images include captions
• Pages display chapter number and chapter/section names
• Sections are numbered
• An electronic version is now available so you can copy+paste scripts
• Example objects .gdl files no longer available
• The example scripts have been moved from an appendix to a chapter, and made more focussed (i.e. less repetition)

Numerous changes have been made to the text;

• To correct spelling and grammar.
• To reduce ambiguity and provide clearer explanation.
• To improve the flow.

Changes to the Content:

• Some sections have been added:
  • Drag-and-drop 2D elements into the 2D script
  • Hotlines in 3D
  • CPrism_{2}
  • Surface area of a body
  • Volume of a body
  • A new example (wine glass)
  • Some sections have been removed:
    • Smart font selection (no longer recommended)
    • Some example scripts (boat & trailer, parts of playground equipment examples)
    • Some sections have been updated:
      • Recommendations for adding fields to a settings dialog
      • Test for the first run of the parameter script
      • Bug fixed in the sub-routine to intersect two line segments
      • Where helpful, footnotes have been added to indicate where changes have been made.