KHR_glsl_shader_versions

extensions/Khronos/KHR_glsl_shader_versions/README.md

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+# KHR\_glsl\_shader\_versions
+
+## Contributors
+
+* Johannes van Waveren, Oculus VR, <mailto:[email protected]>
+
+## Status
+
+Draft (not ratified yet)
+
+## Dependencies
+
+Written against the [glTF 1.0 specification](#references).
+
+## Overview
+
+The [glTF 1.0 specification](#references) only allows [GLSL 1.0 ES](#references) shaders.
+While these shaders work with both OpenGL and OpenGL ES, the GLSL 1.0 ES specification
+is very limiting and does not expose many of the features that enable efficient rendering
+on modern GPUs.
+
+This extension allows a glTF shader to specify multiple GLSL shaders for different graphics APIs: OpenGL, OpenGL ES and Vulkan,
+allowing the application to choose the most appropriate shader for the platform and use case.
+
+## Shader Extension
+
+Graphics API specific shaders are defined by adding an `extensions` property to a glTF shader, and defining its `KHR_glsl_shader_versions` property.
+
+For example, the following defines a glTF shader with URIs to GLSL source for OpenGL, OpenGL ES and Vulkan:
+
+```javascript
+"shaders": {
+    "shader1": {
+        "extensions": {
+            "KHR_glsl_shader_versions" : [
+                {
+                    "api" : "opengl",
+                    "version" : "140",
+                    "uri" : "opengl_glsl140.vert"
+                },
+                {
+                    "api" : "opengles",
+                    "version" : "130 es",
+                    "extensions" : [
+						{
+							"name" : "GL_OVR_multiview2",
+							"behavior" : "require"
+						}
+                    ],
+					"gltfExtension" : [
+						"KHR_glsl_multi_view"
+					]
+                    "uri" : "opengles_glsl130es.vert"
+                },
+                {
+                    "api" : "vulkan",
+                    "version" : "440 core",
+                    "extensions" : [
+						{
+							"name" : "GL_EXT_shader_io_blocks",
+							"behavior" : "enable"
+						},
+						{
+							"name" : "GL_ARB_enhanced_layouts",
+							"behavior" : "enable"
+						}
+                    ],
+					"gltfExtension" : [
+						"KHR_glsl_view_projection_buffer",
+						"KHR_glsl_layout_vulkan"
+					]
+                    "uri" : "vulkan_glsl450.vert"
+                }
+            ]
+        }
+    }
+}
+```
+
+Usage of the extension must be listed in the `extensionsUsed` array.
+
+```javascript
+"extensionsUsed" : [
+    "KHR_glsl_shader_versions"
+]
+```
+
+## Conformance
+
+If this extension is supported, then the application searches through the available
+shaders to find the most up to date shader version for the graphics API used by the
+application.
+
+## Known Implementations
+
+- Khronos Asynchronous Time Warp Sample for OpenGL<br/>
+  https://github.com/KhronosGroup/Vulkan-Samples/blob/master/samples/apps/atw/atw_opengl.c
+- Khronos Asynchronous Time Warp Sample for Vulkan<br/>
+  https://github.com/KhronosGroup/Vulkan-Samples/blob/master/samples/apps/atw/atw_vulkan.c
+
+<a name="references"></a>
+## References
+
+- The glTF 1.0 specification<br/>
+  https://github.com/KhronosGroup/glTF/tree/master/specification/1.0
+- The glTF 1.0 extension registsry<br/>
+  https://github.com/KhronosGroup/glTF/tree/master/extensions
+- GLSL 1.0 ES used by glTF<br/>
+  https://www.khronos.org/files/opengles_shading_language.pdf