Disable ShapeFix_Shape processing by OCCT during STEP file loads to i…

src/Mod/Import/App/ReaderStep.cpp

@@ -35,6 +35,7 @@
 #include <Base/Exception.h>
 #include <Mod/Part/App/encodeFilename.h>
 #include <Mod/Part/App/ProgressIndicator.h>
+#include <Interface_Static.hxx>
 
 using namespace Import;
 
@@ -61,6 +62,12 @@ void ReaderStep::read(Handle(TDocStd_Document) hDoc)  // NOLINT
     Handle(StepData_StepModel) aStepModel = new StepData_StepModel;
     aStepModel->InternalParameters.InitFromStatic();
     aStepModel->SetSourceCodePage(codePage);
+    // These come from static init read of StepData_ConfParameters however
+    // https://dev.opencascade.org/content/stepcontrolreader-readprecisionvalue says it won't really
+    // affect shape healing performance - a 7.9+ version of OpenCascade might.
+    // aStepModel->InternalParameters.ReadMaxPrecisionMode =
+    // StepData_ConfParameters::ReadMode_MaxPrecision_Preferred ; //  _Forced or _Preferred
+    // aStepModel->InternalParameters.ReadMaxPrecisionVal = Precision::Confusion();
     if (aReader.ReadFile(name8bit.c_str(), aStepModel->InternalParameters) != IFSelect_RetDone) {
 #endif
         throw Base::FileException("Cannot read STEP file", file);
@@ -72,6 +79,19 @@ void ReaderStep::read(Handle(TDocStd_Document) hDoc)  // NOLINT
     pi->NewScope(100, "Reading STEP file...");
     pi->Show();
 #endif
+    // Documentation is at
+    // https://dev.opencascade.org/doc/overview/html/occt_user_guides__step.html#occt_step_2_3_3
+    // in the section read.step.resource.name and read.step.sequence  There is a hidden config file
+    // that controls how step processing is done, and can disable things like Shape Fixes -
+    // ShapeFix_Shape consumes about 25% of the transfer processing time.  This code replaces that
+    // special file.  Note that there are dozens of STEP loader control options in that file; see
+    // src/XSTEPResource/STEP in the OpenCascade source for an example.
+    if (!Interface_Static::SetCVal("read.step.sequence", "")) {
+        // We failed to override the step sequence, but there isn't really an advantage in throwing
+        // an exception or even issuing a warning message - just proceed with the default step read
+        // sequence which will be slower.
+    }
+
     aReader.Transfer(hDoc);
 #if OCC_VERSION_HEX < 0x070500
     pi->EndScope();