Fix for that instanceIndex is confusing in two contexts, use invocationId

src/Three.TSL.js

@@ -626,6 +626,7 @@ export const workgroupBarrier = TSL.workgroupBarrier;
 export const workgroupId = TSL.workgroupId;
 export const workingToColorSpace = TSL.workingToColorSpace;
 export const xor = TSL.xor;
+export const invocationIndex = TSL.invocationIndex;
 
 /*
 // Use this code to generate the export statements dynamically

src/nodes/core/IndexNode.js

@@ -123,6 +123,15 @@ export default IndexNode;
  */
 export const vertexIndex = /*@__PURE__*/ nodeImmutable( IndexNode, IndexNode.VERTEX );
 
+/**
+ * TSL object that represents the global index of a compute shader invocation.
+ * This is the linearized index across all workgroups, equivalent to the global invocation ID.
+ *
+ * @tsl
+ * @type {IndexNode}
+ */
+export const invocationIndex = /*@__PURE__*/ nodeImmutable( IndexNode, IndexNode.INVOCATION_GLOBAL );
+
 /**
  * TSL object that represents the index of either a mesh instance or an invocation of a compute shader.
  *

src/nodes/core/NodeBuilder.js

@@ -1035,6 +1035,18 @@ class NodeBuilder {
 
 	}
 
+	/**
+	 * Returns the global invocation index for compute shaders.
+	 * This is the linearized index of a compute invocation within a grid of workgroups.
+	 *
+	 * @abstract
+	 * @return {string} The invocation index shader string.
+	 */
+	getInvocationIndex() {
+
+		warn( 'Abstract function.' );
+
+	}
 	/**
 	 * Contextually returns either the vertex stage instance index builtin
 	 * or the linearized index of an compute invocation within a grid of workgroups.

src/renderers/webgpu/nodes/WGSLNodeBuilder.js

@@ -1206,6 +1206,18 @@ ${ flowData.code }
 	 *
 	 * @return {string} The instance index.
 	 */
+	getInvocationIndex() {
+
+		if ( this.shaderStage === 'compute' ) {
+
+			return 'invocationIndex';
+
+		}
+
+		throw new Error( 'getInvocationIndex() is only valid in compute shaders' );
+
+	}
+
 	getInstanceIndex() {
 
 		if ( this.shaderStage === 'vertex' ) {
@@ -1214,7 +1226,7 @@ ${ flowData.code }
 
 		}
 
-		return 'instanceIndex';
+ 		throw new Error( 'instanceIndex is only valid in vertex shaders. Use invocationIndex for compute shaders.' );
 
 	}
 
@@ -2319,7 +2331,7 @@ fn main( ${shaderData.varyings} ) -> ${shaderData.returnType} {
 ${ shaderData.directives }
 
 // system
-var<private> instanceIndex : u32;
+var<private> invocationIndex : u32;
 
 // locals
 ${ shaderData.scopedArrays }
@@ -2337,7 +2349,7 @@ ${ shaderData.codes }
 fn main( ${ shaderData.attributes } ) {
 
 	// system
-	instanceIndex = globalId.x
+	invocationIndex = globalId.x
 		+ globalId.y * ( ${ workgroupSizeX } * numWorkgroups.x )
 		+ globalId.z * ( ${ workgroupSizeX } * numWorkgroups.x ) * ( ${ workgroupSizeY } * numWorkgroups.y );