Shading: Refactor Math node and use dynamic inputs.

- Implement dynamic inputs. The second input is now unavailable in single
operand math operators.
- Reimplemenet the clamp option using graph expansion for Cycles.
- Clean up code and unify naming between Blender and Cycles.
- Remove unused code.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D5481

source/blender/blenloader/intern/versioning_cycles.c

@@ -26,6 +26,7 @@
 
 #include "BLI_math.h"
 #include "BLI_string.h"
+#include "BLI_listbase.h"
 #include "BLI_utildefines.h"
 
 #include "DNA_color_types.h"
@@ -185,7 +186,7 @@ static void square_roughness_node_insert(bNodeTree *ntree)
 
     /* Add sqrt node. */
     bNode *node = nodeAddStaticNode(NULL, ntree, SH_NODE_MATH);
-    node->custom1 = NODE_MATH_POW;
+    node->custom1 = NODE_MATH_POWER;
     node->locx = 0.5f * (fromnode->locx + tonode->locx);
     node->locy = 0.5f * (fromnode->locy + tonode->locy);
 
@@ -385,6 +386,46 @@ static void light_emission_unify(Light *light, const char *engine)
   }
 }
 
+/* The B input of the Math node is no longer used for single-operand operators.
+ * Previously, if the B input was linked and the A input was not, the B input
+ * was used as the input of the operator. To correct this, we move the link
+ * from B to A if B is linked and A is not.
+ */
+static void update_math_node_single_operand_operators(bNodeTree *ntree)
+{
+  bool need_update = false;
+
+  for (bNode *node = ntree->nodes.first; node; node = node->next) {
+    if (node->type == SH_NODE_MATH) {
+      if (ELEM(node->custom1,
+               NODE_MATH_SQRT,
+               NODE_MATH_CEIL,
+               NODE_MATH_SINE,
+               NODE_MATH_ROUND,
+               NODE_MATH_FLOOR,
+               NODE_MATH_COSINE,
+               NODE_MATH_ARCSINE,
+               NODE_MATH_TANGENT,
+               NODE_MATH_ABSOLUTE,
+               NODE_MATH_FRACTION,
+               NODE_MATH_ARCCOSINE,
+               NODE_MATH_ARCTANGENT)) {
+        bNodeSocket *sockA = BLI_findlink(&node->inputs, 0);
+        bNodeSocket *sockB = BLI_findlink(&node->inputs, 1);
+        if (!sockA->link && sockB->link) {
+          nodeAddLink(ntree, sockB->link->fromnode, sockB->link->fromsock, node, sockA);
+          nodeRemLink(ntree, sockB->link);
+          need_update = true;
+        }
+      }
+    }
+  }
+
+  if (need_update) {
+    ntreeUpdateTree(NULL, ntree);
+  }
+}
+
 void blo_do_versions_cycles(FileData *UNUSED(fd), Library *UNUSED(lib), Main *bmain)
 {
   /* Particle shape shared with Eevee. */
@@ -526,4 +567,13 @@ void do_versions_after_linking_cycles(Main *bmain)
       }
     }
   }
+
+  if (!MAIN_VERSION_ATLEAST(bmain, 281, 2)) {
+    FOREACH_NODETREE_BEGIN (bmain, ntree, id) {
+      if (ntree->type == NTREE_SHADER) {
+        update_math_node_single_operand_operators(ntree);
+      }
+    }
+    FOREACH_NODETREE_END;
+  }
 }