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 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{Notes}
  32 %
  33 %Using the native Windows implementation, you must supply an image with a mask, or
  34 %the image will not show when dragged. It is not clear if this is a bug
  35 %in Windows or in the wxDragImage implementation. You can add a mask
  36 %with a call to wxImage::SetMaskColour, passing RGB values not likely
  37 %to be in the image. [CURED by creating the ImageList with ILC_MASK]
  38
  39 \wxheading{Derived from}
  40
  41 \helpref{wxObject}{wxobject}
  42
  43 \wxheading{Include files}
  44
  45 <wx/dragimag.h>\\
  46 <wx/generic/dragimgg.h>
  47 \wxheading{Library}
  48
  49 \helpref{wxCore}{librarieslist}
  50
  51
  52 \latexignore{\rtfignore{\wxheading{Members}}}
  53
  54 \membersection{wxDragImage::wxDragImage}\label{wxdragimageconstr}
  55
  56 \func{}{wxDragImage}{\void}
  57
  58 Default constructor.
  59
  60 \func{}{wxDragImage}{\param{const wxBitmap\& }{image}, \param{const wxCursor\& }{cursor = wxNullCursor},
  61  \param{const wxPoint\& }{cursorHotspot = wxPoint(0, 0)}}
  62
  63 Constructs a drag image from a bitmap and optional cursor.
  64
  65 \func{}{wxDragImage}{\param{const wxIcon\& }{image}, \param{const wxCursor\& }{cursor = wxNullCursor},
  66  \param{const wxPoint\& }{cursorHotspot = wxPoint(0, 0)}}
  67
  68 Constructs a drag image from an icon and optional cursor.
  69
  70 \pythonnote{This constructor is called wxDragIcon in wxPython.}
  71
  72 \func{}{wxDragImage}{\param{const wxString\& }{text}, \param{const wxCursor\& }{cursor = wxNullCursor},
  73  \param{const wxPoint\& }{cursorHotspot = wxPoint(0, 0)}}
  74
  75 Constructs a drag image from a text string and optional cursor.
  76
  77 \pythonnote{This constructor is called wxDragString in wxPython.}
  78
  79 \func{}{wxDragImage}{\param{const wxTreeCtrl\& }{treeCtrl}, \param{wxTreeItemId\& }{id}}
  80
  81 Constructs a drag image from the text in the given tree control item, and optional cursor.
  82
  83 \pythonnote{This constructor is called wxDragTreeItem in wxPython.}
  84
  85 \func{}{wxDragImage}{\param{const wxListCtrl\& }{treeCtrl}, \param{long }{id}}
  86
  87 Constructs a drag image from the text in the given tree control item, and optional cursor.
  88
  89 \pythonnote{This constructor is called wxDragListItem in wxPython.}
  90
  91 \func{}{wxDragImage}{\param{const wxCursor\& }{cursor = wxNullCursor},
  92  \param{const wxPoint\& }{cursorHotspot = wxPoint(0, 0)}}
  93
  94 Constructs a drag image an optional cursor. This constructor is only available for
  95 wxGenericDragImage, and can be used when the application
  96 supplies \helpref{wxDragImage::DoDrawImage}{wxdragimagedodrawimage} and \helpref{wxDragImage::GetImageRect}{wxdragimagegetimagerect}.
  97
  98 \wxheading{Parameters}
  99
 100 \docparam{image}{Icon or bitmap to be used as the drag image. The bitmap can
 101 have a mask.}
 102
 103 \docparam{text}{Text used to construct a drag image.}
 104
 105 \docparam{cursor}{Optional cursor to combine with the image.}
 106
 107 \docparam{hotspot}{This parameter is deprecated.}
 108
 109 \docparam{treeCtrl}{Tree control for constructing a tree drag image.}
 110
 111 \docparam{listCtrl}{List control for constructing a list drag image.}
 112
 113 \docparam{id}{Tree or list control item id.}
 114
 115 \membersection{wxDragImage::BeginDrag}\label{wxdragimagebegindrag}
 116
 117 \func{bool}{BeginDrag}{\param{const wxPoint\& }{hotspot}, \param{wxWindow* }{window}, \param{bool}{ fullScreen = false}, \param{wxRect*}{ rect = NULL}}
 118
 119 Start dragging the image, in a window or full screen.
 120
 121 \func{bool}{BeginDrag}{\param{const wxPoint\& }{hotspot}, \param{wxWindow* }{window}, \param{wxWindow*}{ boundingWindow}}
 122
 123 Start dragging the image, using the first window to capture the mouse and the second
 124 to specify the bounding area. This form is equivalent to using the first form,
 125 but more convenient than working out the bounding rectangle explicitly.
 126
 127 You need to then call \helpref{wxDragImage::Show}{wxdragimageshow}
 128 and \helpref{wxDragImage::Move}{wxdragimagemove} to show the image on the screen.
 129
 130 Call \helpref{wxDragImage::EndDrag}{wxdragimageenddrag} when the drag has finished.
 131
 132 Note that this call automatically calls CaptureMouse.
 133
 134 \wxheading{Parameters}
 135
 136 \docparam{hotspot}{The location of the drag position relative to the upper-left corner
 137 of the image.}
 138
 139 \docparam{window}{The window that captures the mouse, and within which the dragging
 140 is limited unless {\it fullScreen} is true.}
 141
 142 \docparam{boundingWindow}{In the second form of the function, specifies the
 143 area within which the drag occurs.}
 144
 145 \docparam{fullScreen}{If true, specifies that the drag will be visible over the full
 146 screen, or over as much of the screen as is specified by {\it rect}. Note that the mouse will
 147 still be captured in {\it window}.}
 148
 149 \docparam{rect}{If non-NULL, specifies the rectangle (in screen coordinates) that
 150 bounds the dragging operation. Specifying this can make the operation more efficient
 151 by cutting down on the area under consideration, and it can also make a visual difference
 152 since the drag is clipped to this area.}
 153
 154 \membersection{wxDragImage::DoDrawImage}\label{wxdragimagedodrawimage}
 155
 156 \func{virtual bool}{DoDrawImage}{\param{wxDC\&}{ dc}, \param{const wxPoint\&}{ pos}}
 157
 158 Draws the image on the device context with top-left corner at the given position.
 159
 160 This function is only available with wxGenericDragImage, to allow applications to
 161 draw their own image instead of using an actual bitmap. If you override this function,
 162 you must also override \helpref{wxDragImage::GetImageRect}{wxdragimagegetimagerect}.
 163
 164 \membersection{wxDragImage::EndDrag}\label{wxdragimageenddrag}
 165
 166 \func{bool}{EndDrag}{\void}
 167
 168 Call this when the drag has finished.
 169
 170 Note that this call automatically calls ReleaseMouse.
 171
 172 \membersection{wxDragImage::GetImageRect}\label{wxdragimagegetimagerect}
 173
 174 \constfunc{virtual wxRect}{GetImageRect}{\param{const wxPoint\&}{ pos}}
 175
 176 Returns the rectangle enclosing the image, assuming that the image is drawn with its
 177 top-left corner at the given point.
 178
 179 This function is available in wxGenericDragImage only, and may be overridden (together with
 180 \helpref{wxDragImage::DoDrawImage}{wxdragimagedodrawimage}) to provide a virtual drawing capability.
 181
 182 \membersection{wxDragImage::Hide}\label{wxdragimagehide}
 183
 184 \func{bool}{Hide}{\void}
 185
 186 Hides the image. You may wish to call this before updating the window
 187 contents (perhaps highlighting an item). Then call \helpref{wxDragImage::Move}{wxdragimagemove}
 188 and \helpref{wxDragImage::Show}{wxdragimageshow}.
 189
 190 \membersection{wxDragImage::Move}\label{wxdragimagemove}
 191
 192 \func{bool}{Move}{\param{const wxPoint\& }{pt}}
 193
 194 Call this to move the image to a new position. The image will only be shown if
 195 \helpref{wxDragImage::Show}{wxdragimageshow} has been called previously (for example
 196 at the start of the drag).
 197
 198 {\it pt} is the position in client coordinates (relative to the window specified in BeginDrag).
 199
 200 You can move the image either when the image is hidden or shown, but in general dragging
 201 will be smoother if you move the image when it is shown.
 202
 203 \membersection{wxDragImage::Show}\label{wxdragimageshow}
 204
 205 \func{bool}{Show}{\void}
 206
 207 Shows the image. Call this at least once when dragging.
 208
 209 \membersection{wxDragImage::UpdateBackingFromWindow}\label{wxdragimageupdatebackingfromwindow}
 210
 211 \constfunc{bool}{UpdateBackingFromWindow}{\param{wxDC\&}{ windowDC}, \param{wxMemoryDC\&}{ destDC},
 212  \param{const wxRect\&}{ sourceRect}, \param{const wxRect\&}{ destRect}}
 213
 214 Override this if you wish to draw the window contents to the backing bitmap
 215 yourself. This can be desirable if you wish to avoid flicker by not having to
 216 redraw the updated window itself just before dragging, which can cause a flicker just
 217 as the drag starts. Instead, paint the drag image's backing bitmap to show the appropriate
 218 graphic {\it minus the objects to be dragged}, and leave the window itself to be updated
 219 by the drag image. This can provide eerily smooth, flicker-free drag behaviour.
 220
 221 The default implementation copies the window contents to the backing bitmap. A new
 222 implementation will normally copy information from another source, such as from its
 223 own backing bitmap if it has one, or directly from internal data structures.
 224
 225 This function is available in wxGenericDragImage only.
 226