occt/src/ExpToCasExe

STEP express schema to OCCT classes

1. Introduction

ExpToCasExe is an auxiliary tool to generate code for implementation of new STEP entities into OCCT. This tool consists of two packages: ExpToCasExe and TKExpress.

ExpToCasExe package is the basic package for generation. It parses the express schema, makes a list of entities described in the schema, and starts generating classes according to the specified lists. This package has the file occt_existed_step_entities.lst witch contains list of STEP entities implemented in OCCT at this moment.

TKExpress package generates files with description of the STEP entities to use in OCCT taking into account their dependencies. Below is a set of generated files using the example of the Condition entity from the StepAP214 package.

• StepAP214_Condition.hxx - contains declaration of the class that describes STEP entity
• StepAP214_Condition.cxx - contains definition of the class that describes STEP entity
• RWStepAP214_RWCondition.hxx - contains declaration of the class that reads (writes) STEP entity from STEP file
• RWStepAP214_RWCondition.cxx - contains definition of the class that reads (writes) STEP entity from STEP file
• category.txt - common file for all generated entities with part of code to insert to RWStepAP214_GeneralModule.cxx file
• fillshared.txt - common file for all generated entities with part of code to insert to RWStepAP214_GeneralModule.cxx file
• inc.txt - common file for all generated entities with part of code to insert to StepAP214_Protocol.cxx
• newvoid.txt - common file for all generated entities with part of code to insert to RWStepAP214_GeneralModule.cxx file
• protocol.txt - common file for all generated entities with part of code to insert to StepAP214_Protocol.cxx file
• readstep.txt - common file for all generated entities with part of code to insert to RWStepAP214_ReadWriteModule.cxx file
• reco.txt - common file for all generated entities with part of code to insert to RWStepAP214_ReadWriteModule.cxx file
• rwinc.txt - common file for all generated entities with part of code to insert to RWStepAP214_ReadWriteModule.cxx file
• steptype.txt - common file for all generated entities with part of code to insert to RWStepAP214_ReadWriteModule.cxx file
• typebind.txt - common file for all generated entities with part of code to insert to RWStepAP214_ReadWriteModule.cxx file
• writestep.txt - common file for all generated entities with part of code to insert to RWStepAP214_ReadWriteModule.cxx file

2. Build

The build process is automated, but has some specifics. ExpToCasExe package contains file exptocas.lex which contains rules for lexical analyzer builder (FLEX), and file exptocas.yacc which contains rules for syntax analyzer builder (GNU Bison).

During build process FLEX and Bison generate the next files:

• FlexLexer.h
• lex.exptocas.cxx
• exptocas.tab.cxx
• exptocas.tab.hxx

These files are placed to the source directory ("src/ExpToCasExe") due to CMAKE script specific. Then standard Visual Studio build process continues.

There is no necessary to include these files to the git repository, due to automatic generation. To change the behaviour of Express schema parser, the user need to modify original files: exptocas.lex and exptocas.yacc.

3. Usage

ExpToCasExe program has the following call pattern:

> ExpToCasExe <schema.exp> [<new.lst> [<existed.lst> [start_index]]]

where:

• schema.exp - file with STEP Express schema
• new.lst - file with list of new STEP entities which we have to generate
• existed.lst - file with list of already implemented STEP entities
• start_index - a first index for entity registration (value of it you can receive after analyse of StepAP214_Protocol.cxx file)

If new.lst file is set to "-" then all entities from Express schema are considered as new.

new.lst and existed.lst are the text files. Line in file describes the class name of STEP entity and to witch OCCT package it's belong. Line has the following format:

item_name package_name [shortname [check_flag(0 or 1) [fillshared_flag(0 or 1) [category]]]]

where:

• item_name is the class name of the STEP entity (ProductDefinitionOrReference for example)
• package_name is the name of the OCCT package (StepBasic for example)
• shortname is the short name of the STEP entity
• check_flag is the flag to generate the Check function in the class
• fillshared_flag is the flag to generate the FillShared function in the class
• category is the name of category to witch entity belongs to

These file can include comments after the symbol "#".

The result of generation consists of several folders:

• two folders (_package_name_ and RW_package_name_) for each package for which new entities were generated.
• a folder Registration with *.txt files with code to copy into common files (see the example in the first section).

For generation, it is easy to copy to separate directory following files:

• ExpToCasExe.exe, TKernel.dll and TKExpress.dll from OCCT
• STEP Express schema
• occt_existed_step_entities.lst from package ExpToCasExe

create a file with needed entities new.lst and from this directory execute command:

> ExpToCasExe.exe schema.exp new.lst occt_existed_step_entities.lst 1000

4. Disclaimer

NOTE: Some STEP schemes may be not fully corresponded to the rules which set in our generator. If during generation we receive a message about syntax error you can try to edit schema file in order to avoid it. Such approach is reasonable if number of errors is small. If there are many errors we have to change existed rules (for debug parser process you can uncomment string "//aScanner.set_debug(1);" in the file exptocas.yacc). TIP: remove upper case from name after SCHEMA key word.

NOTE: Please, take into account that most of existed entities were generated many years ago. Some of them can be not corresponded to last versions of schemes.

For example, we don't have classes for entity:

  ENTITY founded_item
    SUPERTYPE OF ((ONEOF(b_spline_curve_knot_locator, b_spline_curve_segment, b_spline_surface_knot_locator,
                         b_spline_surface_patch, b_spline_surface_strip,
                         boundary_curve_of_b_spline_or_rectangular_composite_surface, box_domain,
                         character_glyph_style_outline, character_glyph_style_stroke, composite_curve_segment,
                         composite_curve_transition_locator, curve_style, curve_style_font, curve_style_font_and_scaling,
                         curve_style_font_pattern, externally_defined_style, fill_area_style,
                         interpolated_configuration_segment, kinematic_path_segment, plane_angle_and_length_pair,
                         plane_angle_and_ratio_pair, point_style, presentation_style_assignment,
                         rectangular_composite_surface_transition_locator, surface_patch, surface_side_style,
                         surface_style_boundary, surface_style_control_grid, surface_style_fill_area,
                         surface_style_parameter_line, surface_style_segmentation_curve, surface_style_silhouette,
                         surface_style_usage, symbol_style, text_style, view_volume)) ANDOR
                  (ONEOF(character_glyph_style_outline, character_glyph_style_stroke, curve_style, curve_style_font,
                         curve_style_font_and_scaling, curve_style_font_pattern, externally_defined_style,
                         fill_area_style, point_style, presentation_style_assignment, surface_side_style,
                         surface_style_boundary, surface_style_control_grid, surface_style_fill_area,
                         surface_style_parameter_line, surface_style_segmentation_curve, surface_style_silhouette,
                         surface_style_usage, symbol_style, text_style)));
  DERIVE
    users : SET [0 : ?] OF founded_item_select := using_items(SELF, []);
  WHERE
    WR1: SIZEOF(users) > 0;
    WR2: NOT (SELF IN users);
  END_ENTITY;

But some of existed entities (for example - composite_curve_segment) must be inherited from this missing entity (at present such existed entities are inherited from Standard_Transient):

  ENTITY composite_curve_segment
  SUBTYPE OF (founded_item);
    transition : transition_code;
    same_sense : BOOLEAN;
    parent_curve : curve;
  INVERSE
    using_curves : BAG[1:?] OF composite_curve FOR segments;
  WHERE
    wr1 : ('AUTOMOTIVE_DESIGN.BOUNDED_CURVE' IN TYPEOF(parent_curve));
  END_ENTITY;  -- 10303-42: geometry_schema 

NOTE: To facilitate the work of those who will use this program after you, it is strongly recommended update the file occt_existed_step_entities.lst after each generation and not to forget to change update date in the first line of this file.