PCL OpenGL GLArea demo

• Type: feature
• Track: B
• Status: done
• Owner: — (lock released; last worked by Codex)
• Opened: 2026-06-21
• Relation: Demo/library request for richer PCL GUI examples.

Goal

Add a small GtkGLArea-backed OpenGL surface to PCL and a rotating triangle demo under examples/gl/, proving that PCL can host GL drawing alongside ordinary forms, labels, and timers.

Scope

• lib/pcl/gl_c.h: minimal GtkGLArea/OpenGL declarations.
• lib/pcl/glarea.pas: TGLArea control with render/resize trampolines and QueueRender.
• examples/gl/triangle.pas: animated OpenGL triangle demo.

Acceptance

• Demo source is present and idiomatic enough to compile once the compiler/PCL surface is stable enough for this feature class.
• Any remaining compiler gaps discovered later get separate Track A tickets.

Log

• 2026-06-21 — Found untracked WIP in lib/pcl/gl_c.h, lib/pcl/glarea.pas, and examples/gl/triangle.pas with no matching ticket; captured it as a working ticket instead of leaving it implicit in the dirty tree.

• 2026-06-21 — HALTED → unfinished/. working/ lock released (no active agent). TGLArea + triangle demo committed as 95a3d9c (lib/pcl/glarea.pas, gl_c.h, examples/gl/).

• 2026-06-22 — DONE in this commit. Fixed the triangle demo's local variable name so pinned v32 resolves the TGLArea instance correctly, and added examples/gl/triangle.pas to the make demos dashboard. Verified direct compile with stable_linux_amd64/default/pinned -Fulib/pcl examples/gl/triangle.pas /tmp/demo_triangle; existing make gui-test is green.