Refine dot node elision and remove unused code (#1522)

Dot nodes were elided in #1152 to prevent creating extra samplers in rasterized shadergen.

This preserves the change written by @kwokcb while keeping the distinction between a topological constant node and a non-topological dot node.

In scenarios where you want to feed a single color to multiple shader nodes in a complex material, using a constant node will force recompilation every time the color is tweaked, we want users to be able to use a dot node to feed the graph, which should allow tweaking the color without having to recompile the shader. Also allows re-using the shader code for material instances differing on this input color.

resources/Materials/TestSuite/stdlib/organization/organization.mtlx

@@ -90,4 +90,14 @@
     </transformmatrix>
     <output name="out" type="vector4" nodename="transformvector1" />
   </nodegraph>
+  <nodegraph name="dot_filename">
+    <dot name="dot1" type="filename">
+      <input name="in" type="filename" value="resources/Images/grid.png" />
+      <input name="note" type="string" value="Checking for spurious samplers" />
+    </dot>
+    <image name="image_color3" type="color3">
+      <input name="file" type="filename" nodename="dot1" />
+    </image>
+    <output name="out" type="color3" nodename="image_color3" />
+  </nodegraph>
 </materialx>

source/MaterialXGenShader/ShaderGraph.cpp

@@ -1027,48 +1027,16 @@ void ShaderGraph::optimize(GenContext& context)
         }
         else if (node->hasClassification(ShaderNode::Classification::DOT))
         {
-            // Dot nodes without modifiers can be elided by moving their connection downstream.
+            // Filename dot nodes must be elided so they do not create extra samplers.
             ShaderInput* in = node->getInput("in");
-            if (in->getChannels().empty())
+            if (in->getChannels().empty() && in->getType() == Type::FILENAME)
             {
                 bypass(context, node, 0);
                 ++numEdits;
             }
         }
-        else if (node->hasClassification(ShaderNode::Classification::IFELSE))
-        {
-            // Check if we have a constant conditional expression
-            ShaderInput* intest = node->getInput("intest");
-            if (!intest->getConnection())
-            {
-                // Find which branch should be taken
-                ShaderInput* cutoff = node->getInput("cutoff");
-                ValuePtr value = intest->getValue();
-                const float intestValue = value ? value->asA<float>() : 0.0f;
-                const int branch = (intestValue <= cutoff->getValue()->asA<float>() ? 2 : 3);
-
-                // Bypass the conditional using the taken branch
-                bypass(context, node, branch);
-
-                ++numEdits;
-            }
-        }
-        else if (node->hasClassification(ShaderNode::Classification::SWITCH))
-        {
-            // Check if we have a constant conditional expression
-            const ShaderInput* which = node->getInput("which");
-            if (!which->getConnection())
-            {
-                // Find which branch should be taken
-                ValuePtr value = which->getValue();
-                const int branch = int(value == nullptr ? 0 : (which->getType() == Type::FLOAT ? value->asA<float>() : value->asA<int>()));
-
-                // Bypass the conditional using the taken branch
-                bypass(context, node, branch);
-
-                ++numEdits;
-            }
-        }
+        // Adding more nodes here requires them to have an input that is tagged
+        // "uniform" in the NodeDef or to handle very specific cases, like FILENAME.
     }
 
     if (numEdits > 0)

source/MaterialXGenShader/ShaderNode.cpp

@@ -135,8 +135,6 @@ const ShaderNodePtr ShaderNode::NONE = createEmptyNode();
 const string ShaderNode::CONSTANT = "constant";
 const string ShaderNode::DOT = "dot";
 const string ShaderNode::IMAGE = "image";
-const string ShaderNode::COMPARE = "compare";
-const string ShaderNode::SWITCH = "switch";
 const string ShaderNode::SURFACESHADER = "surfaceshader";
 const string ShaderNode::SCATTER_MODE = "scatter_mode";
 const string ShaderNode::BSDF_R = "R";
@@ -292,14 +290,6 @@ ShaderNodePtr ShaderNode::create(const ShaderGraph* parent, const string& name,
     {
         newNode->_classification = Classification::TEXTURE | Classification::DOT;
     }
-    else if (nodeDef.getNodeString() == COMPARE)
-    {
-        newNode->_classification = Classification::TEXTURE | Classification::CONDITIONAL | Classification::IFELSE;
-    }
-    else if (nodeDef.getNodeString() == SWITCH)
-    {
-        newNode->_classification = Classification::TEXTURE | Classification::CONDITIONAL | Classification::SWITCH;
-    }
     // Third, check for file texture classification by group name
     else if (groupName == TEXTURE2D_GROUPNAME || groupName == TEXTURE3D_GROUPNAME)
     {

source/MaterialXGenShader/ShaderNode.h

@@ -350,23 +350,18 @@ class MX_GENSHADER_API ShaderNode
         static const uint32_t VOLUME        = 1 << 15; /// A volume shader node
         static const uint32_t LIGHT         = 1 << 16; /// A light shader node
         static const uint32_t UNLIT         = 1 << 17; /// An unlit surface shader node
-        // Specific conditional types
-        static const uint32_t IFELSE        = 1 << 18; /// An if-else statement
-        static const uint32_t SWITCH        = 1 << 19; /// A switch statement
         // Types based on nodegroup
-        static const uint32_t SAMPLE2D      = 1 << 20; /// Can be sampled in 2D (uv space)
-        static const uint32_t SAMPLE3D      = 1 << 21; /// Can be sampled in 3D (position)
-        static const uint32_t GEOMETRIC     = 1 << 22; /// Geometric input
-        static const uint32_t DOT           = 1 << 23; /// A dot node
+        static const uint32_t SAMPLE2D      = 1 << 18; /// Can be sampled in 2D (uv space)
+        static const uint32_t SAMPLE3D      = 1 << 19; /// Can be sampled in 3D (position)
+        static const uint32_t GEOMETRIC     = 1 << 20; /// Geometric input
+        static const uint32_t DOT           = 1 << 21; /// A dot node
     };
 
     static const ShaderNodePtr NONE;
 
     static const string CONSTANT;
     static const string DOT;
     static const string IMAGE;
-    static const string COMPARE;
-    static const string SWITCH;
     static const string SURFACESHADER;
     static const string SCATTER_MODE;
     static const string BSDF_R;