added bool operator to object refs, clarified some doc in the headers

include/OpenImageDenoise/oidn.h

@@ -87,10 +87,10 @@ OIDN_API int oidnGetDevice1i(OIDNDevice device, const char* name);
 // Sets the error callback function of the device.
 OIDN_API void oidnSetDeviceErrorFunction(OIDNDevice device, OIDNErrorFunction func, void* userPtr);
 
-// Returns the first unqueried error code stored for the device, optionally
-// also returning a string message (if not NULL), and clears the stored error.
-// If the device is NULL (e.g. the device creation failed), a thread-local
-// error will be returned.
+// Returns the first unqueried error code stored in the device for the current
+// thread, optionally also returning a string message (if not NULL), and clears
+// the stored error. Can be called with a NULL device as well to check why a
+// device creation failed.
 OIDN_API OIDNError oidnGetDeviceError(OIDNDevice device, const char** outMessage);
 
 // Commits all previous changes to the device.

include/OpenImageDenoise/oidn.hpp

@@ -107,6 +107,11 @@ namespace oidn {
       return handle;
     }
 
+    operator bool() const
+    {
+      return handle != nullptr;
+    }
+
     // Maps a region of the buffer to host memory.
     // If byteSize is 0, the maximum available amount of memory will be mapped.
     void* map(Access access = Access::ReadWrite, size_t byteOffset = 0, size_t byteSize = 0)
@@ -187,6 +192,11 @@ namespace oidn {
       return handle;
     }
 
+    operator bool() const
+    {
+      return handle != nullptr;
+    }
+
     // Sets an image parameter of the filter (stored in a buffer).
     void setImage(const char* name,
                   const BufferRef& buffer, Format format,
@@ -345,6 +355,11 @@ namespace oidn {
       return handle;
     }
 
+    operator bool() const
+    {
+      return handle != nullptr;
+    }
+
     // Sets a boolean parameter of the device.
     void set(const char* name, bool value)
     {
@@ -368,12 +383,14 @@ namespace oidn {
     }
 
     // Returns the first unqueried error code and clears the stored error.
+    // Can be called for a null device as well to check why a device creation failed.
     Error getError()
     {
       return (Error)oidnGetDeviceError(handle, nullptr);
     }
 
     // Returns the first unqueried error code and string message, and clears the stored error.
+    // Can be called for a null device as well to check why a device creation failed.
     Error getError(const char*& outMessage)
     {
       return (Error)oidnGetDeviceError(handle, &outMessage);