API proposal: drag view

[Artem Ananiev]

On 1/14/2013 11:51 PM, steve.x.northover at oracle.com wrote:
> +1
>
> I'd like to see some example code where the tree and table set a default
> image as part of the implementation of these controls.  Applications
> would get a reasonable image for free and be able to override it as
> necessary.  Having and getter is necessary for this.
>
> BTW, the last time I looked, on Windows, when you set image content,
> then you will get a drag image for free.  This doesn't happen on the
> Mac.  We should stop doing this on Windows.

Windows behavior seems to be reasonable to me. Note that we have (at 
least at the Glass level) a custom mime type to specify drag image. Only 
if this mime type is not specified, we check for images, so if 
application wants to transfer an image but doesn't want this image to be 
set as drag cursor, it can be easily implemented.

BTW, this behavior corresponds to what modern browsers do. When dnd is 
started, if one of the mime types is image, it is set as a cursor.

Thanks,

Artem

> Steve
>
> On 14/01/2013 2:09 PM, Richard Bair wrote:
>> HI Pavel!
>>
>> Overall great. I don't see why you can't have a getter. The only way
>> to set the drag view is via an API we control so it seems pretty easy
>> to implement the getter as well. You could either have a DragView
>> class which encapsulates the node/image and the offsetX and offsetY,
>> or you could just break it out into three properties on the DragBoard
>> and save yourself the extra class.
>>
>> I think you should just have an image based dragImage property and
>> dragImageOffsetX and dragImageOffsetY properties. We shouldn't by
>> default put anything in as the drag image, except for a few UI
>> controls. We'll want a ListView, TreeView, TableView, TreeTableView to
>> automatically pre-populate the DragBoard before the onDragDetected
>> code is called, so that those control give you a nice drag image for
>> free but the developer is free to replace it or clear it as they see fit.
>>
>> The developer could use the synchronous version of snapshot. But I
>> think either snapshot should be fixed to be transparent by default
>> instead of a white fill by default or add another snapshot method
>> which produces a transparent fill by default. Basically:
>>
>> source.setOnDragDetected(new EventHandler<MouseEvent>() {
>>      public void handle(MouseEvent event) {
>>          DragBoard db = source.startDragAndDrop(TransferMode.ANY);
>>          db.setContent(…);
>>          db.setDragImage(source.snapshot());
>>          db.setDragImageOffsetX(event.getX());
>>          db.setDragImageOffsetY(event.getY());
>>          event.consume();
>>      }
>> }
>>
>> Maybe also have a convenience method on DragBoard:
>>
>>      db.updateDragImage(node, x, y);
>>
>> which then just calls the 3 setters as appropriate.
>>
>> Richard
>>
>> On Jan 13, 2013, at 11:59 PM, Pavel Safrata<pavel.safrata at oracle.com>
>> wrote:
>>
>>> Hello,
>>> this is a proposal of an API allowing to specify the image floating
>>> with mouse cursor during a drag&drop operation.
>>>
>>> Jira: http://javafx-jira.kenai.com/browse/RT-14730
>>>
>>> I propose to add two methods to DragBoard:
>>> setDragView(Image image, double offsetX, double offsetY)
>>> setDragView(Node node, double offsetX, double offsetY)
>>>
>>> The first one simply uses the given image for the drag view with the
>>> offsetX and offsetY specifying cursor position over the image. The
>>> second one renders the given node to an image and uses the result
>>> (the coordinates being in the node's local space).
>>>
>>> The typical usage will look like this:
>>>         sourceNode.setOnDragDetected(new EventHandler<MouseEvent>() {
>>>             public void handle(MouseEvent event) {
>>>                 Dragboard db =
>>> source.startDragAndDrop(TransferMode.ANY);
>>>                 ClipboardContent content = ...
>>>                 db.setContent(content);
>>>                 db.setDragView(sourceNode, event.getX(),
>>> event.getY()); // that's it
>>>                 event.consume();
>>>             }
>>>         });
>>>
>>>
>>> This API is meant for telling the operating system what visual cues
>>> to provide, I don't think it is useful (and I'm not sure it is even
>>> possible) to provide getters.
>>>
>>> There is a possibility to provide default drag view - if none of
>>> those methods is called, the default drag view would be an image of
>>> the drag gesture source. This should work nice most of the times.
>>> However, it may cause inconveniences to some existing apps - for
>>> instance a text editor node which puts the selected text on the
>>> DragBoard - after updating FX the application starts to show the
>>> entire editor in the drag view. For this reason I think the default
>>> behavior should remain unchanged.
>>>
>>> Thanks,
>>> Pavel