docs/latex/wx/dragimag.tex

   1 \section{\class{wxDragImage}}\label{wxdragimage}
   2
   3 This class is used when you wish to drag an object on the screen,
   4 and a simple cursor is not enough.
   5
   6 On Windows, the WIN32 API is used to do achieve smooth dragging. On other platforms,
   7 wxGenericDragImage is used. Applications may also prefer to use
   8 wxGenericDragImage on Windows, too.
   9
  10 \pythonnote{wxPython uses wxGenericDragImage on all platforms, but
  11 uses the wxDragImage name.}
  12
  13 To use this class, when you wish to start dragging an image, create a wxDragImage
  14 object and store it somewhere you can access it as the drag progresses.
  15 Call BeginDrag to start, and EndDrag to stop the drag. To move the image,
  16 initially call Show and then Move. If you wish to update the screen contents
  17 during the drag (for example, highlight an item as in the dragimag sample), first call Hide,
  18 update the screen, call Move, and then call Show.
  19
  20 You can drag within one window, or you can use full-screen dragging
  21 either across the whole screen, or just restricted to one area
  22 of the screen to save resources. If you want the user to drag between
  23 two windows, then you will need to use full-screen dragging.
  24
  25 If you wish to draw the image yourself, use wxGenericDragImage and
  26 override \helpref{wxDragImage::DoDrawImage}{wxdragimagedodrawimage} and
  27 \helpref{wxDragImage::GetImageRect}{wxdragimagegetimagerect}.
  28
  29 Please see {\tt samples/dragimag} for an example.
  30
  31 \wxheading{Derived from}
  32
  33 \helpref{wxObject}{wxobject}
  34
  35 \wxheading{Include files}
  36
  37 <wx/dragimag.h>\\
  38 <wx/generic/dragimgg.h>
  39
  40 \latexignore{\rtfignore{\wxheading{Members}}}
  41
  42 \membersection{wxDragImage::wxDragImage}\label{wxdragimageconstr}
  43
  44 \func{}{wxDragImage}{\void}
  45
  46 Default constructor.
  47
  48 \func{}{wxDragImage}{\param{const wxBitmap\& }{image}, \param{const wxCursor\& }{cursor = wxNullCursor},
  49  \param{const wxPoint& }{hotspot = wxPoint(0, 0)}}
  50
  51 Constructs a drag image from a bitmap and optional cursor.
  52
  53 \func{}{wxDragImage}{\param{const wxIcon\& }{image}, \param{const wxCursor\& }{cursor = wxNullCursor},
  54  \param{const wxPoint& }{hotspot = wxPoint(0, 0)}}
  55
  56 Constructs a drag image from an icon and optional cursor.
  57
  58 \pythonnote{This constructor is called wxDragIcon in wxPython.}
  59
  60 \func{}{wxDragImage}{\param{const wxString\& }{text}, \param{const wxCursor\& }{cursor = wxNullCursor},
  61  \param{const wxPoint& }{hotspot = wxPoint(0, 0)}}
  62
  63 Constructs a drag image from a text string and optional cursor.
  64
  65 \pythonnote{This constructor is called wxDragString in wxPython.}
  66
  67 \func{}{wxDragImage}{\param{const wxTreeCtrl\& }{treeCtrl}, \param{wxTreeItemId\& }{id}}
  68
  69 Constructs a drag image from the text in the given tree control item, and optional cursor.
  70
  71 \pythonnote{This constructor is called wxDragTreeItem in wxPython.}
  72
  73 \func{}{wxDragImage}{\param{const wxListCtrl\& }{treeCtrl}, \param{long }{id}}
  74
  75 Constructs a drag image from the text in the given tree control item, and optional cursor.
  76
  77 \pythonnote{This constructor is called wxDragListItem in wxPython.}
  78
  79 \func{}{wxDragImage}{\param{const wxCursor\& }{cursor = wxNullCursor},
  80  \param{const wxPoint& }{hotspot = wxPoint(0, 0)}}
  81
  82 Constructs a drag image an optional cursor. This constructor is only available for
  83 wxGenericDragImage, and can be used when the application
  84 supplies \helpref{wxDragImage::DoDrawImage}{wxdragimagedodrawimage} and \helpref{wxDragImage::GetImageRect}{wxdragimagegetimagerect}.
  85
  86 \wxheading{Parameters}
  87
  88 \docparam{image}{Icon or bitmap to be used as the drag image. The bitmap can
  89 have a mask.}
  90
  91 \docparam{text}{Text used to construct a drag image.}
  92
  93 \docparam{cursor}{Optional cursor to combine with the image.}
  94
  95 \docparam{hotspot}{Position of the hotspot within the new image.}
  96
  97 \docparam{treeCtrl}{Tree control for constructing a tree drag image.}
  98
  99 \docparam{listCtrl}{List control for constructing a list drag image.}
 100
 101 \docparam{id}{Tree or list control item id.}
 102
 103 \membersection{wxDragImage::BeginDrag}\label{wxdragimagebegindrag}
 104
 105 \func{bool}{BeginDrag}{\param{const wxPoint\& }{hotspot}, \param{wxWindow* }{window}, \param{bool}{ fullScreen = FALSE}, \param{wxRect*}{ rect = NULL}}
 106
 107 Start dragging the image, in a window or full screen.
 108
 109 \func{bool}{BeginDrag}{\param{const wxPoint\& }{hotspot}, \param{wxWindow* }{window}, \param{wxWindow*}{ boundingWindow}}
 110
 111 Start dragging the image, using the first window to capture the mouse and the second
 112 to specify the bounding area. This form is equivalent to using the first form,
 113 but more convenient than working out the bounding rectangle explicitly.
 114
 115 You need to then call \helpref{wxDragImage::Show}{wxdragimageshow}
 116 and \helpref{wxDragImage::Move}{wxdragimagemove} to show the image on the screen.
 117
 118 Call \helpref{wxDragImage::EndDrag}{wxdragimageenddrag} when the drag has finished.
 119
 120 Note that this call automatically calls CaptureMouse.
 121
 122 \wxheading{Parameters}
 123
 124 \docparam{hotspot}{The location of the drag position relative to the upper-left corner
 125 of the image.}
 126
 127 \docparam{window}{The window that captures the mouse, and within which the dragging
 128 is limited unless {\it fullScreen} is TRUE.}
 129
 130 \docparam{boundingWindow}{In the second form of the function, specifies the
 131 area within which the drag occurs.}
 132
 133 \docparam{fullScreen}{If TRUE, specifies that the drag will be visible over the full
 134 screen, or over as much of the screen as is specified by {\it rect}. Note that the mouse will
 135 still be captured in {\it window}.}
 136
 137 \docparam{rect}{If non-NULL, specifies the rectangle (in screen coordinates) that
 138 bounds the dragging operation. Specifying this can make the operation more efficient
 139 by cutting down on the area under consideration, and it can also make a visual difference
 140 since the drag is clipped to this area.}
 141
 142 \membersection{wxDragImage::DoDrawImage}\label{wxdragimagedodrawimage}
 143
 144 \func{virtual bool}{DoDrawImage}{\param{wxDC\&}{ dc}, \param{const wxPoint\&}{ pos}}
 145
 146 Draws the image on the device context with top-left corner at the given position.
 147
 148 This function is only available with wxGenericDragImage, to allow applications to
 149 draw their own image instead of using an actual bitmap. If you override this function,
 150 you must also override \helpref{wxDragImage::GetImageRect}{wxdragimagegetimagerect}.
 151
 152 \membersection{wxDragImage::EndDrag}\label{wxdragimageenddrag}
 153
 154 \func{bool}{EndDrag}{\void}
 155
 156 Call this when the drag has finished.
 157
 158 Note that this call automatically calls ReleaseMouse.
 159
 160 \membersection{wxDragImage::GetImageRect}\label{wxdragimagegetimagerect}
 161
 162 \constfunc{virtual wxRect}{GetImageRect}{\param{const wxPoint\&}{ pos}}
 163
 164 Returns the rectangle enclosing the image, assuming that the image is drawn with its
 165 top-left corner at the given point.
 166
 167 This function is available in wxGenericDragImage only, and may be overridden (together with
 168 \helpref{wxDragImage::DoDrawImage}{wxdragimagedodrawimage}) to provide a virtual drawing capability.
 169
 170 \membersection{wxDragImage::Hide}\label{wxdragimagehide}
 171
 172 \func{bool}{Hide}{\void}
 173
 174 Hides the image. You may wish to call this before updating the window
 175 contents (perhaps highlighting an item). Then call \helpref{wxDragImage::Move}{wxdragimagemove}
 176 and \helpref{wxDragImage::Show}{wxdragimageshow}.
 177
 178 \membersection{wxDragImage::Move}\label{wxdragimagemove}
 179
 180 \func{bool}{Move}{\param{const wxPoint\& }{pt}}
 181
 182 Call this to move the image to a new position. The image will only be shown if
 183 \helpref{wxDragImage::Show}{wxdragimageshow} has been called previously (for example
 184 at the start of the drag).
 185
 186 {\it pt} is the position in window coordinates (or screen coordinates if no
 187 window was specified to BeginDrag.
 188
 189 You can move the image either when the image is hidden or shown, but in general dragging
 190 will be smoother if you move the image when it is shown.
 191
 192 \membersection{wxDragImage::Show}\label{wxdragimageshow}
 193
 194 \func{bool}{Show}{\void}
 195
 196 Shows the image. Call this at least once when dragging.
 197
 198 \membersection{wxDragImage::UpdateBackingFromWindow}\label{wxdragimageupdatebackingfromwindow}
 199
 200 \constfunc{bool}{UpdateBackingFromWindow}{\param{wxDC\&}{ windowDC}, \param{wxMemoryDC\&}{ destDC},
 201  \param{const wxRect\&}{ sourceRect}, \param{const wxRect\&}{ destRect}}
 202
 203 Override this if you wish to draw the window contents to the backing bitmap
 204 yourself. This can be desirable if you wish to avoid flicker by not having to
 205 redraw the updated window itself just before dragging, which can cause a flicker just
 206 as the drag starts. Instead, paint the drag image's backing bitmap to show the appropriate
 207 graphic {\it minus the objects to be dragged}, and leave the window itself to be updated
 208 by the drag image. This can provide eerily smooth, flicker-free drag behaviour.
 209
 210 The default implementation copies the window contents to the backing bitmap. A new
 211 implementation will normally copy information from another source, such as from its
 212 own backing bitmap if it has one, or directly from internal data structures.
 213
 214 This function is available in wxGenericDragImage only.
 215