more optimization of geojson writer

Move from strings to sprintfs to be faster still.
Requires manual buffer management of course.

From here we have to move to bson and then to
more compact representations.

Change-Id: I043fe5e4b3308449ac30092fa7128c7475ff47d8

IO/GeoJSON/vtkGeoJSONWriter.cxx

@@ -25,6 +25,10 @@
 
 #include <vtksys/ios/sstream>
 
+#if _MSC_VER
+#define snprintf _snprintf
+#endif
+
 vtkStandardNewMacro(vtkGeoJSONWriter);
 
 #define VTK_GJWRITER_MAXPOINTS 32000
@@ -32,28 +36,59 @@ vtkStandardNewMacro(vtkGeoJSONWriter);
 class vtkGeoJSONWriter::Internals
 {
 public:
-   Internals(vtkGeoJSONWriter *owner) : Owner(owner)
-   {
-     this->Buffer = new std::string;
-     this->Buffer->reserve(VTK_GJWRITER_MAXPOINTS*10);
-   };
-   ~Internals()
-   {
-     delete this->Buffer;
-   }
-   inline void append(const char *newcontent)
-   {
-     this->Buffer->append(newcontent);
-   }
-   inline void append(const double newcontent)
-   {
-     snprintf(buffer, 256, "%g", newcontent);
-     this->Buffer->append(buffer);
-    }
-   std::string *Buffer;
-   char buffer[256];
-   vtkGeoJSONWriter *Owner;
- };
+  Internals()
+  {
+    this->MaxBufferSize = 128;
+    this->Buffer = new char[this->MaxBufferSize];
+    this->Top = this->Buffer;
+  };
+  ~Internals()
+  {
+    delete[] this->Buffer;
+  }
+  inline size_t GetSize()
+  {
+    return this->Top-this->Buffer;
+  }
+  void Clear()
+  {
+    this->Top = this->Buffer;
+  }
+  inline void Grow()
+  {
+    this->MaxBufferSize*=2;
+    //cerr << "GROW " << this->MaxBufferSize << endl;
+    char *biggerBuffer = new char[this->MaxBufferSize];
+    size_t curSize = this->Top-this->Buffer;
+    memcpy(biggerBuffer, this->Buffer, curSize);
+    delete[] this->Buffer;
+    this->Buffer = biggerBuffer;
+    this->Top = this->Buffer+curSize;
+  }
+  inline void append(const char *newcontent)
+  {
+    while (this->Top+strlen(newcontent)>=this->Buffer+this->MaxBufferSize)
+      {
+      this->Grow();
+      }
+    int nchars = sprintf(this->Top, "%s", newcontent);
+    this->Top+=nchars;
+  }
+  inline void append(const double newcontent)
+  {
+    snprintf(this->NumBuffer, 64, "%g", newcontent);
+    while (this->Top+strlen(NumBuffer)>=this->Buffer+this->MaxBufferSize)
+      {
+      this->Grow();
+      }
+     int nchars = sprintf(this->Top, "%s", this->NumBuffer);
+     this->Top+=nchars;
+  }
+  char *Buffer;
+  char *Top;
+  size_t MaxBufferSize;
+  char NumBuffer[64];
+};
 
  //------------------------------------------------------------------------------
  vtkGeoJSONWriter::vtkGeoJSONWriter()
@@ -64,7 +99,7 @@ public:
    this->WriteToOutputString = false;
    this->ScalarFormat = 2;
    this->LookupTable = NULL;
-   this->WriterHelper = new vtkGeoJSONWriter::Internals(this);
+   this->WriterHelper = new vtkGeoJSONWriter::Internals();
  }
 
  //------------------------------------------------------------------------------
@@ -481,18 +516,18 @@ public:
    this->WriterHelper->append("}\n");//feature.geometry
    this->WriterHelper->append("}\n");//feature
 
-   fp->write(this->WriterHelper->Buffer->c_str(), this->WriterHelper->Buffer->size());
-   this->WriterHelper->Buffer->clear();
+   fp->write(this->WriterHelper->Buffer, this->WriterHelper->GetSize());
+   this->WriterHelper->Clear();
 
-  fp->flush();
-  if (fp->fail())
-    {
-    vtkErrorMacro("Problem writing result check disk space.");
-    delete fp;
-    fp = NULL;
-    }
+   fp->flush();
+   if (fp->fail())
+     {
+     vtkErrorMacro("Problem writing result check disk space.");
+     delete fp;
+     fp = NULL;
+     }
 
-  this->CloseFile(fp);
+   this->CloseFile(fp);
 }
 
 //------------------------------------------------------------------------------