[pmeems]

Phase 2 of the polygon triangulation plan: the OpenGL backend now consumes the Core-prepared triangle meshes instead of GL_POLYGON, so concave polygons, interior rings and multipart geometries render on the GPU.

Depends on #66 (stacked; base branch is polygon-triangulation-core).

What changed

• Polygon fills use indexed triangle rendering through the OpenGL 1.1 client-side vertex-array API (glVertexPointer, glDrawElements, glEnableClientState); no GL_POLYGON remains.
• Outlines are drawn from the original rings of VectorRenderScene, so exterior, hole and multipart boundaries are preserved and internal triangle edges are never outlined.
• The convexity and single-ring restrictions are removed; scenes are accepted when every polygon has a usable mesh (complete triangles, in-range indices, finite coordinates). A polygon without a mesh — for example when Core triangulation failed — makes the whole frame report S_FALSE so the coordinator falls back to GDI, never an incorrect GL_POLYGON approximation.
• The rendering coordinator, GDI fallback, framebuffer handling, 64 MiB staging budget and all existing safeguards are unchanged; no COM interface changes.

Tests

• New coverage: concave/L-shaped polygons, one and multiple interior rings, multipart polygons, missing-mesh fallback, no visible internal triangle edges, and GDI/OpenGL pixel equivalence on a concave holed scene. Geometry support decisions are also tested GPU-independently through a test-access hook.
• Debug | x64 builds with no new Level 4 warnings; MapWinGIS.Core.Tests: 311 passed (1 pre-existing network skip); MapWinGIS.ActiveX.Tests: 65 passed (2 pre-existing skips).

Memory

• .ai/memory/architecture/activex.md: replaced the "convex single-ring only" limit with the mesh-based backend contract. No new memory files.

[Julian-MW]

Found one rendering-order regression in the OpenGL path. See the inline comment.

[Copilot]

🟡 Changes recommended

Drawing all fills before outlines exposes earlier polygon boundaries over later overlapping fills, regressing the previous OpenGL and GDI rendering order.

1 open issue

• Draw each polygon outline before rendering the next polygon · New

What changed in this PR

This PR connects the OpenGL backend to the Core triangulation introduced in #66, enabling GPU rendering of concave polygons, holes, and multipart geometry without COM interface changes.

Changes:

• Replaces GL_POLYGON fills with indexed triangles and draws outlines from original rings.
• Validates meshes and falls back to GDI when any polygon lacks a usable mesh.
• Adds geometry-support and rendering tests, including sampled GDI/OpenGL comparisons.

Builds and tests were not run during this review.

File	Description
tests/​MapWinGIS.ActiveX.Tests/​VectorLayerRendererTests.cpp	Adds mesh preparation, rendering checks, and fallback coverage.
tests/​MapWinGIS.ActiveX.Tests/​OpenGlVectorLayerRendererTestAccess.h	Exposes scene-support checks without an OpenGL context.
src/​MapWinGIS.ActiveX/​OpenGlVectorLayerRenderer.h	Documents mesh-based rendering and declares the support hook.
src/​MapWinGIS.ActiveX/​OpenGlVectorLayerRenderer.cpp	Validates meshes, renders indexed fills, and outlines original rings.
.ai/​memory/​architecture/​activex.md	Updates the documented OpenGL support contract.

_{Review effort: Balanced}