KHR_parallax_mapping

extensions/2.0/Khronos/KHR_materials_parallax_mapping/README.md

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+<!--
+Copyright 2015-2022 The Khronos Group Inc.
+SPDX-License-Identifier: CC-BY-4.0
+-->
+
+# KHR\_materials\_parallax\_mapping
+
+## Contributors
+
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+Many materials provide a height-map that can either be used for real geometry displacement or for parallax-mapping.
+This extension defines a way to specify a texture as a height map.
+
+## glTF Schema Updates
+
+The height at a given position is calculated by sampling the given texture and using the red channel. The sampled value is then multiplied with the `heightFactor`.
+The result is used in an implementation defined way to offset all other texture lookups. (See Resources)
+
+This extension does _not_ require the geometry of the object this material is applied to to be modified.
+
+```json
+{
+    "materials":[
+        {
+            "extension": {
+                "KHR_material_parallax_mapping": {
+                    "heightTexture": 0,
+                    "heightFactor": 0.5,
+                }
+            }
+        }
+    ]
+}
+```
+
+### JSON Schema
+
+- [parallaxMapping.schema.json](schema/parallaxMapping.schema.json)
+
+## Known Implementations
+
+Although no implementations of this extension are known, these techniques are used widely by the industry.
+
+## Resources
+* [Introduction](https://en.wikipedia.org/wiki/Parallax_mapping)
+* [Discussion about different implementations](https://learnopengl.com/Advanced-Lighting/Parallax-Mapping)
+* [GPU Gems 2 - Per-Pixel Displacement Mapping with Distance Functions](https://developer.nvidia.com/gpugems/gpugems2/part-i-geometric-complexity/chapter-8-pixel-displacement-mapping-distance-functions)
+* [GPU Gems 3 - Relaxed Cone Stepping for Relief Mapping](https://developer.nvidia.com/gpugems/gpugems3/part-iii-rendering/chapter-18-relaxed-cone-stepping-relief-mapping)
+* [SIGGRAPH Asia 2021 - Tessellation-Free Displacement Mapping for Ray Tracing](https://perso.telecom-paristech.fr/boubek/papers/TFDM/)

extensions/2.0/Khronos/KHR_materials_parallax_mapping/schema/parallaxMapping.schema.json

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+{
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "title": "parallaxMapping",
+    "type": "object",
+    "description": "Reference to a heightmap for parallax mapping.",
+    "allOf": [ { "$ref": "glTFChildOfRootProperty.schema.json" } ],
+    "properties": {
+        "heightTexture": {
+            "allOf": [ { "$ref": "textureInfo.schema.json" } ],
+            "description": "A texture that describes the surface height.",
+        },
+        "heightFactor": {
+            "type": "number",
+            "description": "Used to scale the height map.",
+            "default": 1.0,
+            "minimum": 0.0,
+            "gltf_detailedDescription": "This parameter scales the heightmap. A smaller number makes the effect less noticable, a higher number more prominent."
+
+        },
+        "extensions": { },
+        "extras": { }
+    },
+}