Nodes: IndexNode - `invocationLocalIndex` (#29202)

* add ability to access local_invocation_index

* fix

* add WebGLBackend workaround

* remove log

* make name change per sunag suggestion

* change name

src/nodes/Nodes.js

@@ -11,7 +11,7 @@ export { default as BypassNode, bypass } from './core/BypassNode.js';
 export { default as CacheNode, cache } from './core/CacheNode.js';
 export { default as ConstNode } from './core/ConstNode.js';
 export { default as ContextNode, context, label } from './core/ContextNode.js';
-export { default as IndexNode, vertexIndex, instanceIndex, drawIndex } from './core/IndexNode.js';
+export { default as IndexNode, vertexIndex, instanceIndex, invocationLocalIndex, drawIndex } from './core/IndexNode.js';
 export { default as LightingModel } from './core/LightingModel.js';
 export { default as Node, addNodeClass, createNodeFromType } from './core/Node.js';
 export { default as VarNode, temp } from './core/VarNode.js';

src/nodes/core/IndexNode.js

@@ -33,6 +33,10 @@ class IndexNode extends Node {
 
 			propertyName = builder.getDrawIndex();
 
+		} else if ( scope === IndexNode.INVOCATION_LOCAL ) {
+
+			propertyName = builder.getInvocationLocalIndex();
+
 		} else {
 
 			throw new Error( 'THREE.IndexNode: Unknown scope: ' + scope );
@@ -61,12 +65,14 @@ class IndexNode extends Node {
 
 IndexNode.VERTEX = 'vertex';
 IndexNode.INSTANCE = 'instance';
+IndexNode.INVOCATION_LOCAL = 'invocationLocal';
 IndexNode.DRAW = 'draw';
 
 export default IndexNode;
 
 export const vertexIndex = nodeImmutable( IndexNode, IndexNode.VERTEX );
 export const instanceIndex = nodeImmutable( IndexNode, IndexNode.INSTANCE );
+export const invocationLocalIndex = nodeImmutable( IndexNode, IndexNode.INVOCATION_LOCAL );
 export const drawIndex = nodeImmutable( IndexNode, IndexNode.DRAW );
 
 addNodeClass( 'IndexNode', IndexNode );

src/renderers/webgl-fallback/nodes/GLSLNodeBuilder.js

@@ -607,6 +607,16 @@ ${ flowData.code }
 
 	}
 
+	getInvocationLocalIndex() {
+
+		const workgroupSize = this.object.workgroupSize;
+
+		const size = workgroupSize.reduce( ( acc, curr ) => acc * curr, 1 );
+
+		return `uint( gl_InstanceID ) % ${size}u`;
+
+	}
+
 	getDrawIndex() {
 
 		const extensions = this.renderer.backend.extensions;

src/renderers/webgpu/nodes/WGSLNodeBuilder.js

@@ -629,6 +629,12 @@ ${ flowData.code }
 
 	}
 
+	getInvocationLocalIndex() {
+
+		return this.getBuiltin( 'local_invocation_index', 'invocationLocalIndex', 'u32', 'attribute' );
+
+	}
+
 	getSubgroupSize() {
 
 		this.enableSubGroups();