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