CNA-PLAT-003: EasyGL on GLES/WebGL contexts without GL_NV_polygon_mode or WEBGL_polygon_mode refuses most wireframe triangle draws

CNA snapshot c1c316b9  ·  Known Issues › Platform limitations  ·  source links pinned to c1c316b9

Without a polygon-mode extension EasyGL draws only two bounded stock routes as line loops (non-indexed PositionColor and indexed PositionNormal TriangleLists); every other FillMode::WireFrame triangle draw throws NotSupportedException.

Identifier

CNA-PLAT-003

Category

Platform limitation

Subsystem

Graphics & renderers

Status

Narrowed (partially fixed; describes only what survives)

Verified against

CNA c1c316b9 (c1c316b9c7a846ce8002809c151fcd1af14942c9)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

Yes: see Current tests

Affected contract

RasterizerState.FillMode = WireFrame on the GLES and WebGL EasyGL profiles

Expected behaviour

XNA HiDef supports wireframe fill; OpenGL ES and WebGL have no polygon mode unless an extension provides it.

Actual behaviour at TARGET

EasyGLRenderer.cpp's RequireSupportedFillModeEXT throws NotSupportedException for TriangleList/TriangleStrip draws when wireframe is requested and neither extension is present, with a message pointing at SupportsCapability(GraphicsCapability::WireFrame), unless the draw qualifies for one of two bounded stock routes that draw each triangle as a line loop. CanDrawStockWireframeAsLineLoops takes a single-stream, non-indexed VertexPositionColor TriangleList drawn with the stock effect, clipped in homogeneous space, with no culling, depth, stencil, scissor, bias, multisampling or render target. CanDrawStockIndexedWireframeAsLineLoops takes an indexed 24-byte VertexPositionNormal TriangleList with the stock lit program, keeping face culling and the depth test. TriangleStrip, other vertex layouts, custom, compiled, skinned or PBR effects, render targets, multisampling, scissor, stencil and depth bias still throw, and GraphicsCapability::WireFrame remains false.

Fixed since first recorded: the two line-loop routes (SAMPLE-048, 251bf6c98 and 96b5038de; SAMPLE-055, cefe6c83b).

Source locations

• modules/renderers/easygl/src/EasyGLRenderer.cpp — EasyGLRenderer::RequireSupportedFillModeEXT, CanDrawStockWireframeAsLineLoops and CanDrawStockIndexedWireframeAsLineLoops
• modules/renderers/easygl/tests/CNA/Internal/Renderers/EasyGL/EasyGLWireFrameContractTests.cpp — EasyGLUnsupportedWireFrameTest: both line-loop routes and the refusals

Evidence

Checked by reading the named sources at c1c316b9; nothing was built or executed for this entry.

Independent re-verification: Checked by reading the named sources at c1c316b9; nothing was built or executed for this entry. The shared WireFrame tests (GraphicsDeviceCapabilityTests.cpp) assert that the reported capability matches the actual draw, so both the positive and the refusal arm exist. In CI they run only in the unfiltered general job, which builds the OPENGLES3 identity (an ES context); platform-ci's OPENGL33 leg runs smoke games rather than these fixtures, so no CI job runs them on desktop GL, and which arm the CI ES context takes depends on whether it exposes GL_NV_polygon_mode.

Re-verified at b0e97bb1: 251bf6c98 and 96b5038de (SAMPLE-048) added the non-indexed PositionColor line-loop route and cefe6c83b (SAMPLE-055) the indexed PositionNormal route; RequireSupportedFillModeEXT still throws for every other wireframe triangle draw. Not executed.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

EasyGLUnsupportedWireFrameTest (EasyGLWireFrameContractTests.cpp) covers both line-loop routes and the refusals (multi-stream, instanced and SpriteBatch triangle routes; cull, bias, clipping, multisampling and two-sided stencil state).

Regression test

A GLES/WebGL context test that asserts the capability is false and the draw throws.

Blast radius

Debug wireframe views and wireframe art styles on mobile and browser builds.

Workaround

Check the WireFrame capability and fall back to Solid, or draw line lists.