[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.

[Julian-MW]

[P2] Preserve polygon painter order within a layer. DrawLayerFills currently renders every polygon in the layer before DrawLayerOutlines renders any of their boundaries. The GDI backend (and the previous OpenGL implementation) processes polygons one at a time, filling and outlining each polygon before moving to the next. When two polygons in the same layer overlap, this split pass leaves the earlier polygon's outline visible on top of the later polygon's fill, whereas GDI correctly covers it. Please keep fill/outline ordering per polygon (while still using that polygon's mesh for the fill), and add an overlapping-polygons-in-one-layer parity test.

[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}