AgentSkillsCN

occt-safe

在编写内核代码时，采用OCCT Handle<>空指针检查模式，以有效防止程序崩溃。

SKILL.md
--- frontmatter
name: occt-safe
description: OCCT Handle<> null-check patterns. Use when writing kernel code to prevent crashes.
invocable: true
author: OneCAD
license: MIT
metadata:
  category: kernel
  priority: high

When to Use

  • •Writing any OCCT-touching code
  • •Debugging crashes in kernel
  • •Code review of kernel changes

CRITICAL: Always Null-Check Handle<>

OCCT Handle<> objects can be null. Dereferencing without check = crash.

Safe Patterns

Before accessing shape

cpp
Handle(TopoDS_Shape) shape = ...;
if (shape.IsNull()) {
    // Handle error
    return;
}
// Now safe to use

Before BRep operations

cpp
Handle(Geom_Surface) surface = BRep_Tool::Surface(face);
if (surface.IsNull()) {
    std::cerr << "No surface on face" << std::endl;
    return false;
}

Shape validity check

cpp
if (shape.IsNull()) return false;
BRepCheck_Analyzer analyzer(shape);
if (!analyzer.IsValid()) {
    // Shape is malformed
}

Builder result check

cpp
BRepPrimAPI_MakeBox mkBox(10, 10, 10);
if (!mkBox.IsDone()) {
    // Construction failed
    return;
}
TopoDS_Shape box = mkBox.Shape();

Common Crash Points

  1. •BRep_Tool::Surface(face) - face may have no surface
  2. •BRep_Tool::Curve(edge) - edge may be degenerate
  3. •TopoDS::Face(shape) - shape may not be a face
  4. •TopExp_Explorer iteration - shapes may be empty
  5. •BRepAlgoAPI_* results - Boolean ops can fail

ElementMap Interaction

cpp
const ElementMapEntry* entry = emap.find(topId);
if (!entry || entry->shape.IsNull()) {
    // Entry doesn't exist or shape was deleted
}