Allow empty vertex program when in "particle" mode

src/Materials/Node/nodeMaterial.ts

@@ -598,7 +598,9 @@ export class NodeMaterial extends PushMaterial {
         this._buildWasSuccessful = false;
         var engine = this.getScene().getEngine();
 
-        if (this._vertexOutputNodes.length === 0) {
+        const allowEmptyVertexProgram = this._mode === NodeMaterialModes.Particle;
+
+        if (this._vertexOutputNodes.length === 0 && !allowEmptyVertexProgram) {
             throw "You must define at least one vertexOutputNode";
         }
 
@@ -622,6 +624,7 @@ export class NodeMaterial extends PushMaterial {
         this._sharedData.emitComments = this._options.emitComments;
         this._sharedData.verbose = verbose;
         this._sharedData.scene = this.getScene();
+        this._sharedData.allowEmptyVertexProgram = allowEmptyVertexProgram;
 
         // Initialize blocks
         let vertexNodes: NodeMaterialBlock[] = [];

src/Materials/Node/nodeMaterialBuildStateSharedData.ts

@@ -111,6 +111,8 @@ export class NodeMaterialBuildStateSharedData {
         notConnectedNonOptionalInputs: new Array<NodeMaterialConnectionPoint>()
     };
 
+    public allowEmptyVertexProgram: boolean = false;
+
     /** Creates a new shared data */
     public constructor() {
         // Exclude usual attributes from free variable names
@@ -154,7 +156,7 @@ export class NodeMaterialBuildStateSharedData {
     public emitErrors() {
         let errorMessage = "";
 
-        if (!this.checks.emitVertex) {
+        if (!this.checks.emitVertex && !this.allowEmptyVertexProgram) {
             errorMessage += "NodeMaterial does not have a vertex output. You need to at least add a block that generates a glPosition value.\r\n";
         }
         if (!this.checks.emitFragment) {