Drag & drop implementation at GHOST level (only OSX for now)

The dragging sequence is performed in four phases:
 
- Start sequence (GHOST_kEventDraggingEntered) that tells a drag'n'drop operation has started. Already gives the object data type, and the entering mouse location

- Update mouse position (GHOST_kEventDraggingUpdated) sent upon each mouse move until the drag'n'drop operation stops, to give the updated mouse position.
Useful to highlight a potential destination, and update the status (through GHOST_setAcceptDragOperation) telling if the object can be dropped at the current cursor position.

- Abort drag'n'drop sequence (GHOST_kEventDraggingExited) sent when the user moved the mouse outside the window.

- Send the dropped data (GHOST_kEventDraggingDropDone)

- Outside of the normal sequence, dropped data can be sent (GHOST_kEventDraggingDropOnIcon). This can happen when the user drops an object on the application icon. (Also used in OSX to pass the filename of the document the user doubled-clicked in the finder)

Note that the event handler is responsible for freeing the received data.
And the mouse position is sent directly in blender client coordinates (y=0 at bottom)

The GHOST_setAcceptDragOperation(TRUE) call must be placed before the user drops the object for it to be accepted.

Current handled data types :
- Text string
- Array of filenames (full paths)
- Bitmap image (not implemented yet)

1 files changed, 21 insertions, 0 deletions

diff --git a/intern/ghost/GHOST_ISystem.h b/intern/ghost/GHOST_ISystem.h
index 08794dfd085..e56a0dae879 100644
--- a/intern/ghost/GHOST_ISystem.h
+++ b/intern/ghost/GHOST_ISystem.h
@@ -351,6 +351,11 @@ public:
 	 */
 	virtual GHOST_TSuccess getButtonState(GHOST_TButtonMask mask, bool& isDown) const = 0;
 
+	
+	/***************************************************************************************
+	 ** Access to clipboard.
+	 ***************************************************************************************/
+	
 	/**
 	 * Returns the selection buffer
 	 * @return Returns "unsinged char" from X11 XA_CUT_BUFFER0 buffer
@@ -363,6 +368,22 @@ public:
 	 */
 	virtual void putClipboard(GHOST_TInt8 *buffer, bool selection) const = 0;
 
+	
+	/***************************************************************************************
+	 ** Drag'n'drop operations
+	 ***************************************************************************************/
+	
+	/**
+	 * Tells if the ongoing drag'n'drop object can be accepted upon mouse drop
+	 */
+	virtual void setAcceptDragOperation(bool canAccept) = 0;
+	
+	/**
+	 * Returns acceptance of the dropped object
+	 * Usually called by the "object dropped" event handling function
+	 */
+	virtual bool canAcceptDragOperation() const = 0;
+	
 protected:
 	/**
 	 * Initialize the system.