Overview
ISO/IEC 9636-4:1991 specifies the segment functionality of the Computer Graphics Interface (CGI) used to create, modify and manage graphic pictures composed of grouped graphic primitives. Part 4 of ISO/IEC 9636 focuses on segment storage and the interface functions that operate on segments - including creation, reopening, closing, copying, renaming and deletion - and the mechanisms for rendering, regeneration and inquiry. Annexes A and B are integral; Annexes C and D provide informative guidance.
Keywords: ISO/IEC 9636-4, CGI segments, computer graphics interface, segment storage, graphic object pipeline.
Key Topics
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Segment identification and lifecycle
- Each Segment has a unique Segment identifier; identifiers may be reused after deletion.
- Segments are created with CREATE SEGMENT, closed with CLOSE SEGMENT and can be reopened (REOPEN SEGMENT). At most one Segment may be open at a time.
- GET NEW SEGMENT IDENTIFIER returns an available identifier for client use.
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Segment content and immutability
- Graphic objects (primitives with attributes) are appended to segments during definition; objects in a segment cannot be modified or removed individually once stored.
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Segment attributes and behaviour
- Attributes covered include visibility, transformation, highlighting, detectability, display priority, and pick priority.
- Attributes influence rendering, feedback (e.g., highlighting for user interaction), and input association for picking.
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Display and regeneration
- Functions and modes for segment display, quick update methods, explicit segment display and segment regeneration are defined, including handling of segment storage overflow.
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Copying, inheritance and picking
- COPY SEGMENT semantics and the inheritance filter (including clipping inheritance) determine how attributes and geometry propagate when segments are duplicated.
- Picking and simulate-pick functions tie segments into input mechanisms.
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Inquiry and state management
- Functions to query segment description tables, segment state lists, individual segment states and lists of identifiers in use.
Applications
- Reference for developers implementing CGI-compliant graphics systems or graphics device drivers.
- Useful to software engineers building virtual devices (class OUTPUT and OUTIN), graphics libraries, visualization tools and CAD systems that require structured, reusable scene elements.
- Guidance for implementers concerned with rendering pipelines, pick input behavior, segment-level updates and storage management.
Related Standards
This standard is essential when designing interoperable, standards-compliant CGI implementations that manage reusable graphic segments and predictable rendering and input behavior.