\begindata{text,539756272} \textdsversion{12} \template{default} \define{overbar } \define{footnote } \formatnote{\formatnote{.ds CT .ds CB - IV-\\\\n(PN -}} \chapter{\overbar{ }Drag & Drop Extensions for the Andrew Toolkit \underline{ } } \flushright{Todd A. Inglett IBM Rochester tinglett@rchland.vnet.ibm.com }\section{ }\center{\bold{\italic{ABSTRACT }}}\indent{\indent{The ability to drag and drop files represented by icons is relatively new to Unix\footnote{\ \begindata{fnote,539676936} \textdsversion{12} Unix is a registered trademark of UNIX System Laboratories, Inc.\ \enddata{fnote,539676936} \view{fnotev,539676936,84,0,0}} with the advent of desktop managers such as \italic{X.desktop}\footnote{\ \begindata{fnote,539677192} \textdsversion{12} X.desktop is a product from IXI Limited, Cambridge, England.\ \enddata{fnote,539677192} \view{fnotev,539677192,85,0,0}} and \italic{Looking Glass}\footnote{\ \begindata{fnote,539677448} \textdsversion{12} Looking Glass is a product from Visix Software, Inc.\ \enddata{fnote,539677448} \view{fnotev,539677448,86,0,0}}. This paper outlines how the simple protocol used by X.desktop may be used to extend the Andrew Toolkit (ATK) to allow drag and drop between X.desktop and an ATK application. The protocol does not require X.desktop. }}\section{ \begindata{bp,539707208} \enddata{bp,539707208} \view{bpv,539707208,95,0,0} Drag & Drop Defined } The definition of \italic{drag and drop} used in this paper is the ability to ``grab'' some user interface object or icon and move it to some new location. Normally, this movement is performed by some mouse action. The movement itself is called a \italic{drag} operation. For example, using \italic{IXI's X.Desktop} (see figure below) is a desktop manager application where one sees files represented by icons on the desktop. If the user presses and holds the first mouse button over an icon, the icon is ``grabbed.'' Visually, the mouse cursor changes to a hand that appears to be holding a piece of paper. With the button held, the user can move the cursor to a new location and release the mouse button. 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q01104924924a 0840c9248880zl | q011949249246 0cc2492489c8zl | q038e34d33be4 0783861bc670zl | v04zr | v08zr | v18zr | zzo | zzo | \enddata{raster, 539763720} \view{rasterview,539763720,88,0,0}} The real action that occurs normally happens when the icon is dropped. If the icon is a file, dropping the icon may move or copy the file to a new directory. Or if the file icon is dropped on another file icon, the other icon may be assumed to be a program to run with the file as input. The exact action depends upon the icon being dropped and the location where it is dropped. IXI's X.desktop offers a script language very similar to the Unix shell to define these actions. Drag and drop operations are not limited to a single window. For example, the \typewriter{runapp.c} icon above can be dragged into another directory window. The physical file will be moved and the icon will move to reflect that fact. The same icon can also be dragged to a \italic{desktop} window. A desktop is not a directory, but simply a holding place for ``working'' files. But these examples are all specific to IXI's X.desktop. Drag and drop operations are not limited to a single application either (such as X.desktop). An icon can be dropped on a different application's window. \section{Drag & Drop and the Andrew Toolkit } Andrew applications can easily exploit the drag and drop paradigm. For example, one could drag a filename out from bush and drop it on ez. Ez could then visit the dropped file. Or a buffer could be dragged out of ez and dropped on bush. Bush could then view the directory containing that file. A file could be dropped onto a typescript, and typescript could enter the file's full pathname onto the command line. As these examples show, the ``objects'' manipulated with drag and drop need not be represented as icons.\footnote{\ \begindata{fnote,539677704} \textdsversion{12} Although one could argue that the presence of an icon makes the operation more intuitive.\ \enddata{fnote,539677704} \view{fnotev,539677704,89,0,0}} Drag and drop in ATK can also be used \italic{within} applications. For example, zip could be implemented such that the drawing object icons are dragged into the drawing area, then edited to suit the drawing. A circle could be dragged and dropped into the drawing, then stretched into shape. The idea becomes very powerful when it is compatible with other non-ATK applications and toolkits. The effectiveness of cut and paste would be seriously impaired if every application or toolkit supported its own incompatible implementation. Likewise, drag and drop would be much less effective if it was confined only to ATK based applications. When ATK honors IXI's drag and drop protocol, X.desktop file icons can be dragged from the desktop and dropped on any ATK application. Bush can be used to find a file which can then be dragged out of bush and dropped on the desktop. These files can be dragged from the desktop onto ez which can either switch to the file or open new windows. The desktop becomes a ``working area'' for frequently used files and directories. \section{IXI's Drag and Drop Protocol } IXI's protocol is based upon creating X \italic{properties} and sending client messages. The protocol ``drops'' a file by creating a property on the window of the destination application followed by sending a client message to the application indicating the name of the property. The client is responsible for reading and deleting the property. No sockets, message queues, streams or other forms of IPC are necessary. The protocol can be monitored and reverse engineered quite readily with the \italic{xprop -spy} command. For readers unfamiliar with X properties, a \italic{property} is logically a variable with a name, type and value that is attached to an X window. It is a programming entity only so it is not visible in any way to a user viewing the window. A \italic{client message} is a short message that can be sent from one X application to another. These messages are delivered in the same manner as any other X protocol event (such as \italic{expose}, \italic{keypress}, \italic{mouse motion}, etc). Because a client message must be short (5 integers plus some window ID information), the protocol uses a property to store the information about the file drop (names, etc), and the client message refers to the property by name and window id. For sake of discussion, call the application performing the drop as ``the sender'' and the application being dropped upon as ``the receiver.'' The protocol works as follows: \description{1. The receiver attaches a property called \italic{IXI_DROP_PROTOCOL} to its own window at startup time. The following table describes this property in detail. The presence of this propery indicates the willingness of the application to receive file drops, and its content describes what window should receive the drop client message. \ \begindata{table,539763976} \cols 96 191 99 - - | ^Protocol Property Definition = =| - - | prop name | IXI_DROP_PROTOCOL =| | type | WINDOW =| | length | '# of formats =| | data[0] | Window ID =| | data[1]... | Supported data types =| - - \enddata{table,539763976} \view{spread,539763976,90,0,0}\center{ } The \italic{data[0]} field indicates the window id which the recipient application wishes to receive the client message. This is normally the same window, but a multi-window application may choose to direct all messages to a single window without requiring the user to only drop objects on that window. The data[1]...data[length] fields indicate the names of data formats that the recipient can interpret. The type \italic{STRING} may be used to indicate a single filename. Normally a full pathname is used. The type \italic{HOST_AND_FILE_NAME} may be used to indicate a list of filenames defined as follows: \example{ hostname\\0pathname1\\0pathname2\\0...\\0pathnameN\\0\\0 } Other data types can be used provided that application's can agree on their usage. 2. The user wants to drop a file. He performs some action in the sender application to initiate a file drop. This is perhaps just a mouse press, but may be a menu selection or key press of some sort. The sender application normally grabs the mouse cursor, changes its shape to indicate a ``drag'' operation, and allows the user to pick a target window. 3. The sender application gets the window id of the receiver application by computing which window was selected in step #2. The sender now traverses the X window tree up from the selected window through parent windows to the root window, looking for a window with an attached \italic{IXI_DROP_PROTOCOL} property. ATK applications normally have only one X window, but other toolkits use subwindows. 4. If the sender cannot find such a window, it aborts the drop. The receiver application does not support drag and drop. 5. If the sender does find such a window, it reads the value of the \italic{IXI_DROP_PROTOCOL} property mentioned in step #1--which contains a window id and data type. Normally this is the same window where the property was found, but it need not be. The sender examines the data types supported by the receiver and converts the data if necessary. The sender then computes a unique property name and creates it on the receiver's window. A unique property name may be generated by using the following template for a name: \example{ IXI_DROP_PROTOCOL_\italic{w}_\italic{x} } Where \italic{w} is the window ID (decimal) of the sender's window, and \italic{x} is some generation number (decimal) used within the sender. If all applications follow this convention, the name should be unique and should not exist on the recipient's window.\footnote{\ \begindata{fnote,539677960} \textdsversion{12} \define{italic menu:[Font~1,Italic~11] attr:[FontFace Italic Int Set]} Ideally, the sender will reuse the generation numbers when the property is deleted by the recipient. This avoids core leaks in the X server because \italic{atoms} must be created for these names.\ \enddata{fnote,539677960} \view{fnotev,539677960,91,0,0}} 6. Assuming the data type indicates a ``file drop'', the sender places the names of the dropped files into the property it has just created. The receiver is not yet aware of the events that have taken place thus far. 7. The sender finally forms a client message to send to the receiver. The following table describes this message which is sent as a client message to the receiver: \ \begindata{table,539764232} - - | ^Client Message Format = =| - - | event type | ClientMessage =| | window | Receiver's window id =| | message type | IXI_DROP_PROTOCOL =| | format | '32 =| | data[0] | time stamp =| | data[1] | coordinates =| | data[2] | mouse state =| | data[3] | data format =| | data[4] | property name =| - - \enddata{table,539764232} \view{spread,539764232,92,0,0} The \italic{coordinates} is a 32 bit integer formed as follows: \ \begindata{table,539764104} \cols 200 199 99 '31 "0 - - | x coordinate | y coordinate =| - - \enddata{table,539764104} \view{spread,539764104,93,0,0} The \italic{mouse state} is a 32 bit integer formed as follows: \ \begindata{table,539764488} \cols 99 127 60 99 99 '32 "13 "8 "0 - - - - | reserved (0's) = | buttons | modifiers =| - - - - \enddata{table,539764488} \view{spread,539764488,94,0,0} The \italic{buttons} field is 5 bits and contains one bit for mouse buttons 1 through 5. For example, bits 8 and 9 set indicates that buttons 1 and 2 were pressed when the ``object'' was dragged (although they may have been released to drop the file). The \italic{modifiers} field is 8 bits and contains one bit for each of the modifier keys \italic{shift}, \italic{lock}, \italic{control}, and \italic{mod1} through \italic{mod5}. The \italic{data format} field of the client message specifies the data type of the property that was stored on the recipient's window. This is usually \italic{HOST_AND_FILE_NAME} and must match one of the data types supported by the recipient application. The \italic{property name} field of the client message indicates the name of the property so the recipient can find it. 8. The receiver gets the client message as an X event. It locates the property by name, reads its value, and deletes the property. The receiver may do what it wishes with the file names (visit a file, etc). The receiver can use the mouse button state and x,y coordinates to perform different operations depending upon which buttons were used to drop the file and where the file was dropped. } \section{The ATK Interface } The sample implementation was done by adding three new methods to the \italic{interaction manager}. The interaction manager was chosen because it best represents an instance of an ATK window. The three methods are: \typewriter{im_DropFiles(char **pathnames, struct cursor *cursor) im_DropFile(char *pathname, struct cursor *cursor) }\leftindent{These methods allow an application to drag ``out'' of the application. Currently only file drags are implemented and the second method is simply a convenience function for the first. The im_DropFiles method takes a null terminated list of file names and a cursor. The file names are those that will be dropped. This method grabs the cursor and changes it to the given cursor and allows the user to select a point to drop the files. The application is blocked until the drop occurs at which time the method returns. } \typewriter{char **im_GetDroppedFiles() }\leftindent{This method is used to get files dropped on a view. It returns a null terminated list of filenames that where dropped, or NULL if there are no dropped files. Currently, only file drops are implemented. The protocol by which a view ``sees'' that files have been dropped is described below. } The application is informed of a file ``drop'' exactly as it is informed of a mouse ``hit.'' In fact, the list of mouse actions has been extended to include file drops in the view interface: \example{enum view_MouseAction \{ view_NoMouseEvent, view_LeftDown, view_LeftUp, view_LeftMovement, view_RightDown, view_RightUp, view_RightMovement, \bold{view_LeftFileDrop}, \bold{view_MiddleFileDrop}, \bold{view_RightFileDrop} \}; } When a file is dropped on an ATK application, the drop is indicated as a mouse hit. The hit filters down the view tree as any ordinary mouse hit. In order to allow insets to interpret file drops, a view should always pass a file drop hit down to a child view first, after which it should attempt to get the files that were dropped with im_GetDroppedFiles. If the child view called im_GetDroppedFiles, there will be no files to get, i.e. im_GetDroppedFiles may only be called once. This allows the child view to ``take'' the files. If the child view does not handle file drops, it's hit method simply returns and the parent view gets the files. This protocol gives the child view precedence so that files may be dropped on individual insets. One problem with the protocol is that it is assumed that each view's hit method passes unknown hits down to their child views. Unfortunately, this is not always the case. Already, the scrollview class has been modified to pass unknown hits to its child view. The dropped file names are discarded if no view accepts the dropped files. \section{ATK Examples } So far only ez and typescript have been modified to use the above drag and drop interface. For both, a new proctable call is available that may be bound to a menu or key which will initiate a file drop. In ez the filename associated with the current buffer is the file that is dragged and dropped. In typescript the current working directory is dragged...which is only useful if the shell's prompt prints the \typewriter{^A^B} title hack string. Dropping a collection of files on ez will perform a visit file operation. If the files are dropped with the left button, new windows appear for each file dropped. If the files are dropped with the right button several visit files are performed within the same window leaving the last file visible. Dropping a collection of files on typescript will enter the full pathnames of the files onto the command line at the current insertion point. \section{Future Work } Currently, the interfaces concentrate on \italic{file} drag and drop even though the protocol should support any type of drag and drop. The interface should be extended to allow for arbitrary typed drag and drop. Perhaps the im_GetDroppedFiles() method could be replaced by im_GetDroppedObject(struct atom *type) and could return a vector of ``objects.'' The im_DropFiles method blocks the application while the user drops files. This is not always acceptible and should be worked into the im main application loop. Perhaps a worthy goal would be to enhance im enough that the drag and drop could be separated into a class of its own. This would require externalizing X window properties and client messages...both of which could be useful for implementing a form of IPC between ATK applications. The OSF has recently announced Motif 1.2 which also includes the concept of drag and drop. Before ATK interfaces are set in stone, these interfaces and protocols should be examined so that ATK might interoperate with newer versions of Motif. \enddata{text,539756272}