wxDragImage

This class is used when you wish to drag an object on the screen, and a simple cursor is not enough.

On Windows, the WIN32 API is used to do achieve smooth dragging. On other platforms, wxGenericDragImage is used. Applications may also prefer to use wxGenericDragImage on Windows, too.

wxPython note: wxPython uses wxGenericDragImage on all platforms, but uses the wxDragImage name.

To use this class, when you wish to start dragging an image, create a wxDragImage object and store it somewhere you can access it as the drag progresses. Call BeginDrag to start, and EndDrag to stop the drag. To move the image, initially call Show and then Move. If you wish to update the screen contents during the drag (for example, highlight an item as in the dragimag sample), first call Hide, update the screen, call Move, and then call Show.

You can drag within one window, or you can use full-screen dragging either across the whole screen, or just restricted to one area of the screen to save resources. If you want the user to drag between two windows, then you will need to use full-screen dragging.

If you wish to draw the image yourself, use wxGenericDragImage and override wxDragImage::DoDrawImage and wxDragImage::GetImageRect.

Please see samples/dragimag for an example.

Derived from

wxObject

Include files

<wx/dragimag.h>
<wx/generic/dragimgg.h>

Members

wxDragImage::wxDragImage
wxDragImage::BeginDrag
wxDragImage::DoDrawImage
wxDragImage::EndDrag
wxDragImage::GetImageRect
wxDragImage::Hide
wxDragImage::Move
wxDragImage::Show
wxDragImage::UpdateBackingFromWindow

wxDragImage::wxDragImage

wxDragImage()

Default constructor.

wxDragImage(const wxBitmap& image, const wxCursor& cursor = wxNullCursor, const wxPoint& cursorHotspot = wxPoint(0, 0))

Constructs a drag image from a bitmap and optional cursor.

wxDragImage(const wxIcon& image, const wxCursor& cursor = wxNullCursor, const wxPoint& cursorHotspot = wxPoint(0, 0))

Constructs a drag image from an icon and optional cursor.

wxPython note: This constructor is called wxDragIcon in wxPython.

wxDragImage(const wxString& text, const wxCursor& cursor = wxNullCursor, const wxPoint& cursorHotspot = wxPoint(0, 0))

Constructs a drag image from a text string and optional cursor.

wxPython note: This constructor is called wxDragString in wxPython.

wxDragImage(const wxTreeCtrl& treeCtrl, wxTreeItemId& id)

Constructs a drag image from the text in the given tree control item, and optional cursor.

wxPython note: This constructor is called wxDragTreeItem in wxPython.

wxDragImage(const wxListCtrl& treeCtrl, long id)

Constructs a drag image from the text in the given tree control item, and optional cursor.

wxPython note: This constructor is called wxDragListItem in wxPython.

wxDragImage(const wxCursor& cursor = wxNullCursor, const wxPoint& cursorHotspot = wxPoint(0, 0))

Constructs a drag image an optional cursor. This constructor is only available for wxGenericDragImage, and can be used when the application supplies wxDragImage::DoDrawImage and wxDragImage::GetImageRect.

Parameters

image

Icon or bitmap to be used as the drag image. The bitmap can have a mask.

text

Text used to construct a drag image.

cursor

Optional cursor to combine with the image.

hotspot

This parameter is deprecated.

treeCtrl

Tree control for constructing a tree drag image.

listCtrl

List control for constructing a list drag image.

id

Tree or list control item id.

wxDragImage::BeginDrag

bool BeginDrag(const wxPoint& hotspot, wxWindow* window, bool fullScreen = false, wxRect* rect = NULL)

Start dragging the image, in a window or full screen.

bool BeginDrag(const wxPoint& hotspot, wxWindow* window, wxWindow* boundingWindow)

Start dragging the image, using the first window to capture the mouse and the second to specify the bounding area. This form is equivalent to using the first form, but more convenient than working out the bounding rectangle explicitly.

You need to then call wxDragImage::Show and wxDragImage::Move to show the image on the screen.

Call wxDragImage::EndDrag when the drag has finished.

Note that this call automatically calls CaptureMouse.

Parameters

hotspot

The location of the drag position relative to the upper-left corner of the image.

window

The window that captures the mouse, and within which the dragging is limited unless fullScreen is true.

boundingWindow

In the second form of the function, specifies the area within which the drag occurs.

fullScreen

If true, specifies that the drag will be visible over the full screen, or over as much of the screen as is specified by rect. Note that the mouse will still be captured in window.

rect

If non-NULL, specifies the rectangle (in screen coordinates) that bounds the dragging operation. Specifying this can make the operation more efficient by cutting down on the area under consideration, and it can also make a visual difference since the drag is clipped to this area.

wxDragImage::DoDrawImage

virtual bool DoDrawImage(wxDC& dc, const wxPoint& pos)

Draws the image on the device context with top-left corner at the given position.

This function is only available with wxGenericDragImage, to allow applications to draw their own image instead of using an actual bitmap. If you override this function, you must also override wxDragImage::GetImageRect.

wxDragImage::EndDrag

bool EndDrag()

Call this when the drag has finished.

Note that this call automatically calls ReleaseMouse.

wxDragImage::GetImageRect

virtual wxRect GetImageRect(const wxPoint& pos) const

Returns the rectangle enclosing the image, assuming that the image is drawn with its top-left corner at the given point.

This function is available in wxGenericDragImage only, and may be overridden (together with wxDragImage::DoDrawImage) to provide a virtual drawing capability.

wxDragImage::Hide

bool Hide()

Hides the image. You may wish to call this before updating the window contents (perhaps highlighting an item). Then call wxDragImage::Move and wxDragImage::Show.

wxDragImage::Move

bool Move(const wxPoint& pt)

Call this to move the image to a new position. The image will only be shown if wxDragImage::Show has been called previously (for example at the start of the drag).

pt is the position in client coordinates (relative to the window specified in BeginDrag).

You can move the image either when the image is hidden or shown, but in general dragging will be smoother if you move the image when it is shown.

wxDragImage::Show

bool Show()

Shows the image. Call this at least once when dragging.

wxDragImage::UpdateBackingFromWindow

bool UpdateBackingFromWindow(wxDC& windowDC, wxMemoryDC& destDC, const wxRect& sourceRect, const wxRect& destRect) const

Override this if you wish to draw the window contents to the backing bitmap yourself. This can be desirable if you wish to avoid flicker by not having to redraw the updated window itself just before dragging, which can cause a flicker just as the drag starts. Instead, paint the drag image's backing bitmap to show the appropriate graphic minus the objects to be dragged, and leave the window itself to be updated by the drag image. This can provide eerily smooth, flicker-free drag behaviour.

The default implementation copies the window contents to the backing bitmap. A new implementation will normally copy information from another source, such as from its own backing bitmap if it has one, or directly from internal data structures.

This function is available in wxGenericDragImage only.