stub out line material

Author: pmconne

extensions/2.0/Vendor/EXT_materials_CAD_line_style/README.md

@@ -0,0 +1,47 @@
+<!--
+Copyright 2015-2025 The Khronos Group Inc.
+SPDX-License-Identifier: CC-BY-4.0
+-->
+
+# EXT_materials_CAD_line_style
+
+## Contributors
+
+* Paul Connelly, Bentley Systems, [@pmconne](https://github.com/pmconne)
+
+## Status
+
+Complete
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+3D modeling and computer-aided drafting (CAD) environments like SketchUp, MicroStation, and Revit use lines extensively to annotate both two- and three-dimensional visualizations. Different lines are rendered with different styles to convey particular semantics and/or differing levels of emphasis. A CAD line style specifies the width of the line and a dash pattern. The EXT_materials_CAD_line_style augments a material with a description of a CAD line style.
+
+## Example
+
+
+[open question: device-pixel-ratio for width and pixel patterns?]
+
+## glTF Schema Updates
+
+The `EXT_materials_CAD_line_style` extension is applied to a material. If that material is used by any line-type primitive, or by the edges described by the `EXT_mesh_primitive_edge_visibility` extension, then it dictates the width and pattern with which the lines are to be drawn.
+
+The `width` property specifies the length of 
+
+
+## Implementation Notes
+
+[tesselation generally required for width > 1 because many graphics APIs like WebGL no longer support wide line primitives]
+[implementation may smooth out the tesselated lines by, e.g., inserting triangles at the joints]
+[pattern should be continuous along the length of a line string]
+[patterns could be aggregated into a texture]
+
+## JSON Schema
+
+- [EXT_mesh_primitive_restart.schema.json](schema/EXT_mesh_primitive_restart.schema.json)
+- [primitiveGroup.schema.json](schema/primitiveGroup.schema.json)
+