The pipeline class owns the portal_stencil shader + a dynamic VBO/VAO
for per-frame portal triangle uploads. MarkAndPunch runs WB's two-step
stencil setup (mark portals = 1, then write gl_FragDepth=1.0 into
stencil=1 regions). EnableOutdoorPass switches to read-only stencil
for the subsequent terrain + outdoor-entity passes.
PortalMeshBuilder.BuildTriangles is the pure-math triangle-fan
extractor — unit-testable without a GL context. Only exit portals
(OtherCellId == 0xFFFF) are emitted; inner portals are skipped to
prevent outdoor geometry from bleeding into adjacent rooms.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
