TSL: Add `premult` and `unpremult` (#31114)

* fix clear texture and facing away if `bounce` is `false`

* add `premult`, `unpremult`

* cleanup

examples/jsm/tsl/display/GaussianBlurNode.js

@@ -1,36 +1,10 @@
 import { RenderTarget, Vector2, NodeMaterial, RendererUtils, QuadMesh, TempNode, NodeUpdateType } from 'three/webgpu';
-import { nodeObject, Fn, If, float, uv, uniform, convertToTexture, vec2, vec4, passTexture, mul } from 'three/tsl';
+import { nodeObject, Fn, float, uv, uniform, convertToTexture, vec2, vec4, passTexture, mul, premult, unpremult } from 'three/tsl';
 
 const _quadMesh = /*@__PURE__*/ new QuadMesh();
 
 let _rendererState;
 
-const premult = /*@__PURE__*/ Fn( ( [ color ] ) => {
-
-	return vec4( color.rgb.mul( color.a ), color.a );
-
-} ).setLayout( {
-	name: 'premult',
-	type: 'vec4',
-	inputs: [
-		{ name: 'color', type: 'vec4' }
-	]
-} );
-
-const unpremult = /*@__PURE__*/ Fn( ( [ color ] ) => {
-
-	If( color.a.equal( 0.0 ), () => vec4( 0.0 ) );
-
-	return vec4( color.rgb.div( color.a ), color.a );
-
-} ).setLayout( {
-	name: 'unpremult',
-	type: 'vec4',
-	inputs: [
-		{ name: 'color', type: 'vec4' }
-	]
-} );
-
 /**
  * Post processing node for creating a gaussian blur effect.
  *

src/Three.TSL.js

@@ -385,6 +385,7 @@ export const pow = TSL.pow;
 export const pow2 = TSL.pow2;
 export const pow3 = TSL.pow3;
 export const pow4 = TSL.pow4;
+export const premult = TSL.premult;
 export const property = TSL.property;
 export const radians = TSL.radians;
 export const rand = TSL.rand;
@@ -509,6 +510,7 @@ export const uniform = TSL.uniform;
 export const uniformArray = TSL.uniformArray;
 export const uniformGroup = TSL.uniformGroup;
 export const uniforms = TSL.uniforms;
+export const unpremult = TSL.unpremult;
 export const userData = TSL.userData;
 export const uv = TSL.uv;
 export const uvec2 = TSL.uvec2;

src/nodes/display/BlendModes.js

@@ -1,4 +1,4 @@
-import { Fn, vec4 } from '../tsl/TSLBase.js';
+import { Fn, If, vec4 } from '../tsl/TSLBase.js';
 import { mix, min, step } from '../math/MathNode.js';
 
 /**
@@ -130,6 +130,47 @@ export const blendColor = /*@__PURE__*/ Fn( ( [ base, blend ] ) => {
 	]
 } );
 
+/**
+ * Premultiplies the RGB channels of a color by its alpha channel.
+ *
+ * This function is useful for converting a non-premultiplied alpha color
+ * into a premultiplied alpha format, where the RGB values are scaled
+ * by the alpha value. Premultiplied alpha is often used in graphics
+ * rendering for certain operations, such as compositing and image processing.
+ *
+ * @tsl
+ * @function
+ * @param {Node<vec4>} color - The input color with non-premultiplied alpha.
+ * @return {Node<vec4>} The color with premultiplied alpha.
+ */
+export const premult = /*@__PURE__*/ Fn( ( [ color ] ) => {
+
+	return vec4( color.rgb.mul( color.a ), color.a );
+
+}, { color: 'vec4', return: 'vec4' } );
+
+/**
+ * Unpremultiplies the RGB channels of a color by its alpha channel.
+ *
+ * This function is useful for converting a premultiplied alpha color
+ * back into a non-premultiplied alpha format, where the RGB values are
+ * divided by the alpha value. Unpremultiplied alpha is often used in graphics
+ * rendering for certain operations, such as compositing and image processing.
+ *
+ * @tsl
+ * @function
+ * @param {Node<vec4>} color - The input color with premultiplied alpha.
+ * @return {Node<vec4>} The color with non-premultiplied alpha.
+ */
+export const unpremult = /*@__PURE__*/ Fn( ( [ color ] ) => {
+
+	If( color.a.equal( 0.0 ), () => vec4( 0.0 ) );
+
+	return vec4( color.rgb.div( color.a ), color.a );
+
+}, { color: 'vec4', return: 'vec4' } );
+
+
 // Deprecated
 
 /**