added SkSL support for mustForceNegatedAtanParamToFloat cap

src/sksl/SkSLGLSLCodeGenerator.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
  
 #include "SkSLGLSLCodeGenerator.h"
 
 #include "string.h"
@@ skipping 145 matching lines @@
             this->writeMinAbsHack(*c.fArguments[0], *c.fArguments[1]);
             return;
         }
         if (is_abs(*c.fArguments[1])) {
             // note that this violates the GLSL left-to-right evaluation semantics. I doubt it will
             // ever end up mattering, but it's worth calling out.
             this->writeMinAbsHack(*c.fArguments[1], *c.fArguments[0]);
             return;
         }
     }
+    if (fCaps.fMustForceNegatedAtanParamToFloat && c.fFunction.fName == "atan" && 
+        c.fArguments.size() == 2 && c.fArguments[1]->fKind == Expression::kPrefix_Kind) {
+        const PrefixExpression& p = (PrefixExpression&) *c.fArguments[1];
+        if (p.fOperator == Token::MINUS) {
+            this->write("atan(");
+            this->writeExpression(*c.fArguments[0], kSequence_Precedence);
+            this->write(", -1.0 * ");
+            this->writeExpression(*p.fOperand, kMultiplicative_Precedence);
+            this->write(")");
+            return;
+        }
+    }
     this->write(c.fFunction.fName + "(");
     const char* separator = "";
     for (const auto& arg : c.fArguments) {
         this->write(separator);
         separator = ", ";
         this->writeExpression(*arg, kSequence_Precedence);
     }
     this->write(")");
 }
 
@@ skipping 457 matching lines @@
                 break;
             default:
                 printf("%s\n", e->description().c_str());
                 ABORT("unsupported program element");
         }
     }
     fOut = nullptr;
 }
 
 }