Feature/1187 Read EXR files from memory

vtkext/private/module/vtkF3DEXRReader.cxx

@@ -10,6 +10,7 @@
 #include <ImfArray.h>
 #include <ImfRgbaFile.h>
 
+#include <cstring>
 #include <sstream>
 #include <thread>
 
@@ -38,13 +39,13 @@
   this->ComputeInternalFileName(this->DataExtent[4]);
   if (this->InternalFileName == nullptr || this->InternalFileName[0] == '\0')
   {
-    return;
+    // If we have no file then maybe we have the file in memory
+    if (!this->MemoryBuffer)
+      return;
   }
 
-  try
+  auto execute = [&](Imf::RgbaInputFile& file)
   {
-    Imf::RgbaInputFile file(this->InternalFileName);
-
     Imath::Box2i dw = file.dataWindow();
     this->DataExtent[0] = dw.min.x;
     this->DataExtent[1] = dw.max.x;
@@ -56,6 +57,21 @@
     {
       throw std::runtime_error("only RGB and RGBA channels are supported");
     }
+  };
+
+  try
+  {
+    if (this->MemoryBuffer)
+    {
+      MemStream memoryStream("EXRmemoryStream", this->MemoryBuffer, this->MemoryBufferLength);
+      Imf::RgbaInputFile file = Imf::RgbaInputFile(memoryStream);
+      execute(file);
+    }
+    else
+    {
+      Imf::RgbaInputFile file(this->InternalFileName);
+      execute(file);
+    }
   }
   catch (const std::exception& e)
   {
@@ -112,12 +128,8 @@
   scalars->SetName("Pixels");
   float* dataPtr = scalars->GetPointer(0);
 
-  try
+  auto execute = [&](Imf::RgbaInputFile& file)
   {
-    assert(this->InternalFileName);
-    Imf::setGlobalThreadCount(std::thread::hardware_concurrency());
-    Imf::RgbaInputFile file(this->InternalFileName);
-
     Imf::Array2D<Imf::Rgba> pixels(this->GetHeight(), this->GetWidth());
 
     file.setFrameBuffer(&pixels[0][0], 1, this->GetWidth());
@@ -134,6 +146,24 @@
         dataPtr += 3;
       }
     }
+  };
+
+  try
+  {
+    assert(this->InternalFileName);
+    Imf::setGlobalThreadCount(std::thread::hardware_concurrency());
+
+    if (this->MemoryBuffer)
+    {
+      MemStream memoryStream("EXRmemoryStream", this->MemoryBuffer, this->MemoryBufferLength);
+      Imf::RgbaInputFile file = Imf::RgbaInputFile(memoryStream);
+      execute(file);
+    }
+    else
+    {
+      Imf::RgbaInputFile file(this->InternalFileName);
+      execute(file);
+    }
   }
   catch (const std::exception& e)
   {
@@ -142,6 +172,24 @@
   }
 }
 
+//------------------------------------------------------------------------------
+/**
+ * Read from memory instead of file
+ */
+void vtkF3DEXRReader::SetMemoryBuffer(const void* buff)
+{
+  this->MemoryBuffer = buff;
+}
+
+//------------------------------------------------------------------------------
+/**
+ * Specify the in memory image buffer length.
+ */
+void vtkF3DEXRReader::SetMemoryBufferLength(vtkIdType bufferLen)
+{
+  this->MemoryBufferLength = bufferLen;
+}
+
 //------------------------------------------------------------------------------
 int vtkF3DEXRReader::GetWidth() const
 {
@@ -153,3 +201,15 @@
 {
   return this->DataExtent[3] - this->DataExtent[2] + 1;
 }
+
+//------------------------------------------------------------------------------
+bool vtkF3DEXRReader::MemStream::read(char c[], int n)
+{
+  if (pos + n <= bufflen)
+  {
+    memcpy(c, buffer + pos, n);
+    pos += n;
+    return true;
+  }
+  return false;
+}

vtkext/private/module/vtkF3DEXRReader.h

@@ -3,6 +3,8 @@
 
 #include "vtkImageReader.h"
 
+#include <OpenEXR/ImfIO.h>
+
 class vtkF3DEXRReader : public vtkImageReader
 {
 public:
@@ -31,6 +33,16 @@
     return "OpenEXR";
   }
 
+  /**
+   * Read from memory instead of file
+   */
+  void SetMemoryBuffer(const void* buff) override;
+
+  /**
+   * Specify the in memory image buffer length.
+   */
+  void SetMemoryBufferLength(vtkIdType buflen) override;
+
 protected:
   vtkF3DEXRReader();
   ~vtkF3DEXRReader() override;
@@ -44,6 +56,52 @@
 private:
   vtkF3DEXRReader(const vtkF3DEXRReader&) = delete;
   void operator=(const vtkF3DEXRReader&) = delete;
+
+  /**
+   * Class to treat file contents in memory like it were still in a file.
+   */
+  class MemStream : public Imf::IStream
+  {
+  public:
+    MemStream(const char* name, const void* buff, vtkIdType bufferLen)
+      : Imf::IStream(name)
+      , buffer(static_cast<const char*>(buff))
+      , bufflen(static_cast<size_t>(bufferLen))
+      , pos(0)
+    {
+    }
+
+    bool read(char c[], int n) override;
+
+    /**
+     * returns the current reading position, in bytes, from the beginning of the file.
+     * The next read() call will begin reading at the indicated position
+     */
+    uint64_t tellg() override
+    {
+      return pos;
+    }
+
+    /**
+     * sets the current reading position to pos bytes from the beginning of the "file"
+     */
+    void seekg(uint64_t new_pos) override
+    {
+      pos = new_pos;
+    }
+
+    /**
+     * clears any error flags (we dont have to worry about this)
+     */
+    void clear() override
+    {
+    }
+
+  private:
+    const char* buffer;
+    size_t bufflen;
+    uint64_t pos;
+  };
 };
 
 #endif