api: Allow Frame to use external memory

Frame allocates memory with new[] by default. Provide a way to not
do that.

Author: xlz

include/libfreenect2/frame_listener.hpp

@@ -58,14 +58,24 @@ class LIBFREENECT2_API Frame
   float gain;             ///< Get the gain set by the color camera.
   float gamma;            ///< Get the gamma level set by the color camera.
 
-  Frame(size_t width, size_t height, size_t bytes_per_pixel) :
+  /** Construct a new frame.
+   * @param width Width in pixel
+   * @param height Height in pixel
+   * @param bytes_per_pixel Bytes per pixel
+   * @param data_ Memory to store frame data. If `NULL`, new memory is allocated.
+   */
+  Frame(size_t width, size_t height, size_t bytes_per_pixel, unsigned char *data_ = NULL) :
     width(width),
     height(height),
     bytes_per_pixel(bytes_per_pixel),
+    data(data_),
     exposure(0.f),
     gain(0.f),
-    gamma(0.f)
+    gamma(0.f),
+    rawdata(NULL)
   {
+    if (data_)
+      return;
     const size_t alignment = 64;
     size_t space = width * height * bytes_per_pixel + alignment;
     rawdata = new unsigned char[space];
@@ -74,7 +84,7 @@ class LIBFREENECT2_API Frame
     data = reinterpret_cast<unsigned char *>(aligned);
   }
 
-  ~Frame()
+  virtual ~Frame()
   {
     delete[] rawdata;
   }