Event Callbacks

yucad notifies the host by calling __stdcall function pointers the host registers — never the reverse.

Registering

Each event type has a CadOnEvent* registrar taking one function pointer. Registering again replaces the previous callback; passing null clears it. There is one callback slot per event type per process, matching Vecad.

void __stdcall onMove(YuHandle hDwg, double x, double y){ /* world coords */ }
CadOnEventMouseMove(onMove);

void __stdcall onCmdFinish(YuHandle hDwg, int cmdId){ /* command completed */ }
CadOnEventCmdFinish(onCmdFinish);

Callback contract

• Callbacks use __stdcall, exactly like the exports.
• They fire on the document's UI thread, synchronously, during the yucad call or message dispatch that triggered them — so it is safe to call back into yucad from inside a handler for the same document.
• Handlers should return promptly; long work blocks the viewport.

Event categories

Custom entities & commands

A host can define its own entity types and commands: yucad calls back for display, grip points, hit-testing, transforms and a name/property list, and drives the whole lifecycle through the custom-entity (CEnt*) callback family and the custom-command family. This lets a host render and edit domain objects the core engine has no built-in knowledge of, while still participating in selection, undo and DXF round-tripping.