BENTLEY_materials_line_style

extensions/2.0/Vendor/BENTLEY_material_line_style/README.md

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+<!--
+Copyright 2015-2025 The Khronos Group Inc.
+SPDX-License-Identifier: CC-BY-4.0
+-->
+
+# BENTLEY_material_line_style
+
+## Contributors
+
+* Paul Connelly, Bentley Systems, [@pmconne](https://github.com/pmconne)
+* Daniel Zhong, Bentley Systems, [@danielzhong](https://github.com/danielzhong)
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+Lines are fundamental elements in many 3D modeling and computer-aided design (CAD) environments. They are used to annotate two- and three-dimensional visualizations, with variations in width and dash patterns conveying semantic meaning or emphasis.  
+
+The `BENTLEY_material_line_style` extension defines a method for describing the visual style of lines within glTF material. It enables authors to specify line thickness and a repeating dash pattern.  
+
+This extension introduces two primary properties controlling line appearance:
+
+- `width`: the pixel width of the rendered line  
+- `pattern`: a string of arbitrary length representing a repeating sequence of lit (`-`) and unlit (` `) pixels
+
+## Specifying Line Styles
+
+The `BENTLEY_material_line_style` extension is applied to a material.  
+When that material is used by any line-type primitive, or by the edges described by the `EXT_mesh_primitive_edge_visibility` extension, it defines the **width** and **pattern** with which those lines are rendered.
+
+### Width
+
+The `width` property specifies the line’s thickness **in screen pixels**.  
+The value of `width` must be greater than `0`.  
+
+For each line segment, implementations should extrude geometry by half this width on each side of the segment’s centerline, perpendicular to its direction.
+
+
+### Pattern
+
+The `pattern` property specifies a **repeating on/off pixel sequence** to be applied along the length of the line.  
+It is expressed as a string of arbitrary length, where each character corresponds to one pixel:
+
+- `-` (hyphen): lit pixel (on)  
+- ` ` (space): unlit pixel (off)
+
+The pattern repeats cyclically once the end of the string is reached.  
+The first character determines whether the first pixel drawn is lit or unlit.
+
+Example patterns:
+
+| Pattern | Description |
+|----------|--------------|
+| `---` | solid line |
+| `- -` | dotted line |
+| `--  ` | dashed line |
+| `- - --  -` | custom pattern |
+
+The pattern is applied continuously along each continuous line string or loop.
+
+## Implementation Notes
+
+Because many graphics APIs do not support line primitives with a width larger than 1, tessellation is generally required to draw wide lines. Implementations may smooth out the tesselated lines by, e.g., inserting additional triangles at the joints to round them.
+
+The pattern should be continuous along the length of each continuous line string or line loop.
+
+Implementations may choose to aggregate the set of unique dash patterns into a texture with one row per pattern to be indexed by the shader program when applying a line style's pattern.
+
+## JSON Schema
+
+* [material.BENTLEY_material_line_style.schema.json](schema/material.BENTLEY_material_line_style.schema.json)

extensions/2.0/Vendor/BENTLEY_material_line_style/schema/material.BENTLEY_material_line_style.schema.json

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+{
+  "$schema": "http://json-schema.org/draft-04/schema",
+  "title": "BENTLEY_material_line_style extension",
+  "type": "object",
+  "description": "Specifies line width and dash pattern for CAD-style visualization.",
+  "allOf": [
+    { "$ref": "glTFProperty.schema.json" }
+  ],
+  "properties": {
+    "width": {
+      "type": "number",
+      "description": "Width of the line in screen pixels. Must be > 0.",
+      "minimum": 0
+    },
+    "pattern": {
+      "type": "string",
+      "description": "Arbitrary-length bitfield string representing on/off pattern. '-' = lit, ' ' = unlit."
+    },
+    "extensions": {},
+    "extras": {}
+  },
+  "required": ["width", "pattern"]
+}