Volume 6A: Motif Programming Manual

Arg args[10];

int n;

Widget label;

Atom importList[1];

void HandleDrop();

...

n = 0;

importList[0] = COMPOUND_TEXT;

XtSetArg (args[n], XmNimportTargets, importList); n++;

XtSetArg (args[n], XmNnumImportTargets, XtNumber (importList)); n++;

XtSetArg (args[n], XmNdropSiteOperations, XmDROP_COPY); n++;

XtSetArg (args[n], XmNdropProc, HandleDrop); n++;

XmDropSiteRegister (label, args, n);

When a drop occurs in the drop site, the XmN-dropProc is called automatically by the Motif toolkit. This routine

must call XmDropTransferStart() whether or not the drop is -successful. XmDropTransferStart()

creates a DropTransfer object that maintains information about the data transfer. When The DropTransfer object is

created, the XmN-transferStatus resource must be set to indicate the success or failure of the drop. If the

resource is set to XmTRANSFER_FAILURE, XmDropTransferStart() does not transfer any data and merely

cleans up after the drag and drop transfer.

If XmN-transferStatus is set to XmTRANSFER_SUCCESS when the DropTransfer object is created, some other

resources must also be specified to cause the data to be transferred. The XmN-dropTransfers and

XmN-numDropTransfers resources specify the data targets to be processed, while XmN-transferProc

indicates the procedure that receives the converted data from the drag source. This procedure is of type

XtSelectionCallbackProc. Once the data transfer has started, XmDropTransferAdd() can be used to

request the processing of additional data targets. In Section #sdropsite, we discuss in detail the tasks involved in

creating a drop site.

When a drop takes place, visual effects are used to indicate the status of the transfer. Unlike the different drag effects,

these visuals are not customizable. When the drop occurs, the pointer shape is changed back to the standard cursor,

while the drag icon sits over the drop site. If the drop succeeds, the icon melts into the drop site. If the transfer fails or

is cancelled by the user, the icon snaps back to the drag source.

A drop site is normally the size and shape of the widget with which it is associated. However, a drop site can also be

shaped. The XmN-dropRectangles and XmN-numDropRectangles resources control this feature. Drop sites

can also be nested, so that a manager widget can be a drop site and can also contain children that are drop sites. The

XmN-dropSiteType resource controls whether the drop site is a simple drop site or a compound drop site. Drop

sites have a stacking order, which means that they can overlap. When drop sites overlap, the drop site on the top of the

stack obscures the drop sites beneath it, as you would expect. An application can control the stacking order of drop

sites using XmDropSiteQueryStackingOrder() and XmDropSiteConfigureStackingOrder().

19.2.3 The Drag Icon

During a drag, the pointer shape is changed into a drag icon that represents the data that is being dragged. One of the

purposes of the special icon is to make it clear that a drag and drop transfer is in progress. The drag icon can also

change during a drag to indicate the current status of the transfer. These visual effects are called drag−over visuals.

Typical effects include changing the shape and changing the color of the icon.

A drag icon can be composed of three distinct parts, each of which is really a separate icon. The source icon

represents the type of data that is being dragged; this icon is the only necessary component of a drag icon. The source

icon for a drag that manipulates files might be an image of a piece of paper, for example. The state icon indicates

19 Drag and Drop 19.2.3 The Drag Icon

519

whether the pointer is over a valid drop site, over an invalid drop site, or not over a drop site. The operation icon

specifies the current operation. The source icon in a drag icon is static, while the state and operation icons can be

dynamic. the figure shows the components of a drag icon.

A drag icon

The Motif toolkit provides default icons for all of the different drag icon components. The default source icons for

textual data and for generic data are shown in the figure.

Default source icons

The default state icon for all of the different states is an arrow, as shown in the figure, while the default operation

icons for the move, copy, and link operations are shown in the figure.

Default operation icons

Motif uses DragIcon objects to represent the parts of a drag icon. In order to use a custom image, you need to create

each part of the icon using XmCreateDragIcon(). The XmN-blendModel resource of the DragContext for a

drag and drop transfer specifies the different pieces that are blended together to create the actual drag icon.

A drag icon is essentially a pixmap, and the DragIcon object encapsulates all of the information about the image.

When you create a DragIcon, you specify resources that describe the image. The XmN-pixmap and XmN-mask

resources represent the actual pixmap and its mask if you use one. Other resources include XmN-height,

19 Drag and Drop 19.2.3 The Drag Icon

520