Stricter check for eliding for Shader Optimization (#2754)

This is a follow up to the PR #2746.

Me and @rasmustilljander continued to look into issues related to upgrading our MaterialX 1.38 materials to MaterialX 1.39.
The PR #2746 solved an issue for custom nodes getting classified as CONSTANTS but without inputs. However, we discover some more appearances having shaders generated with syntax errors not fixed by last PR. This PR tightens the check to make sure only constant/dot nodes are elided.

Author: bowald

source/MaterialXGenShader/ShaderGraph.cpp

@@ -97,7 +97,7 @@ void ShaderGraph::createConnectedNodes(const ElementPtr& downstreamElement,
         {
             continue;
         }
-        
+
         InputPtr graphInput = activeInput->getInterfaceInput();
         if (graphInput && graphInput->hasDefaultGeomPropString())
         {
@@ -978,9 +978,9 @@ void ShaderGraph::optimize(GenContext& context)
     {
         if (node->hasClassification(ShaderNode::Classification::CONSTANT))
         {
-            if (node->numInputs() == 0)
+            if (node->numInputs() != 1 || node->numOutputs() != 1)
             {
-                // Cannot elide a constant node with no inputs.
+                // Constant node doesn't follow expected interface, cannot elide.
                 continue;
             }
             // Constant nodes can be elided by moving their value downstream.
@@ -1003,9 +1003,9 @@ void ShaderGraph::optimize(GenContext& context)
         }
         else if (node->hasClassification(ShaderNode::Classification::DOT))
         {
-            if (node->numInputs() == 0)
+            if (node->numOutputs() != 1)
             {
-                // Cannot elide a dot node with no inputs.
+                // Dot node dosen't follow expected interface, cannot elide.
                 continue;
             }
             // Filename dot nodes must be elided so they do not create extra samplers.