KHR_blend

extensions/2.0/Khronos/KHR_blend/README.md

@@ -0,0 +1,96 @@
+# KHR_blend
+
+## Contributors
+
+TODO
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+This extension defines blending operations on glTF materials. The `KHR_blend`
+extension may be used alongside the default PBR materials, or materials defined
+in glTF extensions. When combined with other materials and techniques, blending
+may be used to achieve effects like fire, steam, or holograms.
+
+For any material with the `KHR_blend` extension, blending must use the
+specified blend equation/operation and factors.
+
+For any materials without the `KHR_blend` extension, blending is assumed to be
+off unless otherwise specified.
+
+### Properties
+
+**blendEquation** :white_check_mark:
+
+Determines how a new pixel is combined with a pixel already in the frame buffer.
+
+* **Type:** `number` `[2]`
+    - `0` *color* equation
+    - `1` *alpha* equation
+* **Required:** Yes
+* **Allowed values:**
+
+| name                     | blendEquation | description |
+|--------------------------|---------------|-------------|
+| FUNC_ADD                 | 0x8006        | Set an addition blend function. |
+| FUNC_SUBTRACT            | 0x800A        | Specify a subtraction blend function (source - destination). |
+| FUNC_REVERSE_SUBTRACT    | 0x800B        | Specify a reverse subtraction blend function (destination - source). |
+| MIN                      | 0x8007        | Produces the minimum color components of the source and destination colors. |
+| MAX                      | 0x8008        | Produces the maximum color components of the source and destination colors. |
+
+**blendFactors** :white_check_mark:
+
+Defines parameters to the blending equation.
+
+* **Type:** `number` `[4]`
+    - `0` : *source color* multiplier
+    - `1` : *destination color* multiplier
+    - `2` : *source alpha* multiplier
+    - `3` : *destination alpha* multiplier
+* **Required:** Yes
+* **Allowed values:**
+
+| name                | blendFactor | description |
+|---------------------|-------------|-------------|
+| ZERO                | 0           | Turn off a component. |
+| ONE                 | 1           | Turn on a component. |
+| SRC_COLOR           | 0x0300      | Multiply a component by the source's color. |
+| ONE_MINUS_SRC_COLOR | 0x0301      | Multiply a component by one minus the source's color. |
+| SRC_ALPHA           | 0x0302      | Multiply a component by the source's alpha. |
+| ONE_MINUS_SRC_ALPHA | 0x0303      | Multiply a component by one minus the source's alpha. |
+| DST_ALPHA           | 0x0304      | Multiply a component by the destination's alpha. |
+| ONE_MINUS_DST_ALPHA | 0x0305      | Multiply a component by one minus the destination's alpha. |
+| DST_COLOR           | 0x0306      | Multiply a component by the destination's color. |
+| ONE_MINUS_DST_COLOR | 0x0307      | Multiply a component by one minus the destination's color. |
+
+### Example
+
+```json
+"materials": [
+    {
+        "name": "My_Additive_Material",
+        "pbrMetallicRoughness": {},
+        "extensions": {
+            "KHR_blend": {
+                "blendEquation": [32778, 32778],
+                "blendFactors": [1, 1, 1, 1]
+            }
+        }
+    }
+]
+ ```
+
+## glTF Schema Updates
+
+**JSON schema**: TODO
+
+## Known Implementations
+
+TODO

extensions/README.md

@@ -3,6 +3,7 @@
 ## Extensions for glTF 2.0
 
 #### Khronos extensions
+* [KHR_blend](2.0/Khronos/KHR_blend/README.md)
 * [KHR_materials_pbrSpecularGlossiness](2.0/Khronos/KHR_materials_pbrSpecularGlossiness/README.md)
 * [KHR_materials_unlit](2.0/Khronos/KHR_materials_unlit/README.md)
 * [KHR_draco_mesh_compression](2.0/Khronos/KHR_draco_mesh_compression/README.md)