qcanvas.3qt

Linux下的基于X11的图形开发环境。

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.TE
.fi
</center>
.PP
The QCanvas is initially sized to show exactly the given number of tiles horizontally and vertically. If it is resized to be larger, the entire matrix of tiles will be repeated as much as necessary to cover the area. If it is smaller, tiles to the right and bottom will not be visible.
.PP
See also setTiles().
.SH "QCanvas::~QCanvas ()\fC [virtual]\fR"
Destroys the canvas and all the canvas's canvas items.
.SH "void QCanvas::advance ()\fC [virtual slot]\fR"
Moves all QCanvasItem::animated() canvas items on the canvas and refreshes all changes to all views of the canvas. (An `animated' item is an item that is in motion; see setVelocity().)
.PP
The advance takes place in two phases. In phase 0, the QCanvasItem::advance() function of each QCanvasItem::animated() canvas item is called with paramater 0. Then all these canvas items are called again, with parameter 1. In phase 0, the canvas items should not change position, merely examine other items on the canvas for which special processing is required, such as collisions between items. In phase 1, all canvas items should change positions, ignoring any other items on the canvas. This two-phase approach allows for considerations of "fairness", although no QCanvasItem subclasses supplied with Qt do anything interesting in phase 0.
.PP
The canvas can be configured to call this function periodically with setAdvancePeriod().
.PP
See also update().
.SH "QCanvasItemList QCanvas::allItems ()"
Returns a list of all items in the canvas.
.SH "QColor QCanvas::backgroundColor () const"
Returns the color set by setBackgroundColor(). By default, this is white.
.PP
This function is not a reimplementation of QWidget::backgroundColor() (QCanvas is not a subclass of QWidget), but all QCanvasViews that are viewing the canvas will set their backgrounds to this color.
.PP
See also setBackgroundColor() and backgroundPixmap().
.SH "QPixmap QCanvas::backgroundPixmap () const"
Returns the pixmap set by setBackgroundPixmap(). By default, this is a null pixmap.
.PP
See also setBackgroundPixmap() and backgroundColor().
.SH "int QCanvas::chunkSize () const"
Returns the chunk size of the canvas.
.PP
See also retune().
.SH "QCanvasItemList QCanvas::collisions ( const QPoint & p ) const"
Returns a list of canvas items that collide with the point \fIp\fR. The list is ordered by z coordinates, from highest z coordinate (front-most item) to lowest z coordinate (rear-most item).
.SH "QCanvasItemList QCanvas::collisions ( const QRect & r ) const"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Returns a list of items which collide with the rectangle \fIr\fR. The list is ordered by z coordinates, from highest z coordinate (front-most item) to lowest z coordinate (rear-most item).
.SH "QCanvasItemList QCanvas::collisions ( const QPointArray & chunklist, const QCanvasItem * item, bool exact ) const"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Returns a list of canvas items which intersect with the chunks listed in \fIchunklist\fR, excluding \fIitem\fR. If \fIexact\fR is TRUE, only those which actually QCanvasItem::collidesWith() \fIitem\fR are returned; otherwise canvas items are included just for being in the chunks.
.PP
This is a utility function mainly used to implement the simpler QCanvasItem::collisions() function.
.SH "void QCanvas::drawArea ( const QRect & clip, QPainter * painter, bool dbuf = FALSE )"
Paints all canvas items that are in the area \fIclip\fR to \fIpainter\fR, using double-buffering if \fIdbuf\fR is TRUE.
.PP
e.g. to print the canvas to a printer:
.PP
.nf
.br
  QPrinter pr;
.br
  if ( pr.setup() ) {
.br
    QPainter p(&pr);
.br
    canvas.drawArea( canvas.rect(), &p );
.br
  }
.br
.fi
.PP
Example: canvas/canvas.cpp.
.SH "void QCanvas::drawBackground ( QPainter & painter, const QRect & clip )\fC [virtual protected]\fR"
This virtual function is called for all updates of the canvas. It renders any background graphics using the painter \fIpainter\fR, in the area \fIclip\fR. If the canvas has a background pixmap or a tiled background, that graphic is used, otherwise the canvas is cleared using the background color.
.PP
If the graphics for an area change, you must explicitly call setChanged(const QRect&) for the result to be visible when update() is next called.
.PP
See also setBackgroundColor(), setBackgroundPixmap(), and setTiles().
.SH "void QCanvas::drawForeground ( QPainter & painter, const QRect & clip )\fC [virtual protected]\fR"
This virtual function is called for all updates of the canvas. It renders any foreground graphics using the painter \fIpainter\fR, in the area \fIclip\fR.
.PP
If the graphics for an area change, you must explicitly call setChanged(const QRect&) for the result to be visible when update() is next called.
.PP
The default is to draw nothing.
.SH "int QCanvas::height () const"
Returns the height of the canvas, in pixels.
.PP
Example: canvas/canvas.cpp.
.SH "bool QCanvas::onCanvas ( int x, int y ) const"
Returns TRUE if the pixel position (\fIx\fR, \fIy\fR) is on the canvas; otherwise returns FALSE.
.PP
See also validChunk().
.SH "bool QCanvas::onCanvas ( const QPoint & p ) const"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Returns TRUE if the pixel position \fIp\fR is on the canvas; otherwise returns FALSE.
.PP
See also validChunk().
.SH "QRect QCanvas::rect () const"
Returns a rectangle the size of the canvas.
.SH "void QCanvas::resize ( int w, int h )\fC [virtual]\fR"
Changes the size of the canvas to have a width of \fIw\fR and a height of \fIh\fR. This is a slow operation.
.PP
Examples:
.)l canvas/canvas.cpp and chart/chartform.cpp.
.SH "void QCanvas::resized ()\fC [signal]\fR"
This signal is emitted whenever the canvas is resized. Each QCanvasView connects to this signal to keep the scrollview size correct.
.SH "void QCanvas::retune ( int chunksze, int mxclusters = 100 )\fC [virtual]\fR"
Change the efficiency tuning parameters to \fImxclusters\fR clusters, each of size \fIchunksze\fR. This is a slow operation if there are many objects on the canvas.
.PP
The canvas is divided into chunks which are rectangular areas of the canvas \fIchunksze\fR wide by \fIchunksze\fR high. Use a chunk size which is about the average size of the canvas items. If you choose a chunk size which is too small it will increase the amount of calculation required when drawing since each change will affect many chunks. If you choose a chunk size which is too large the amount of drawing required will increase because for each change, a lot of drawing will be required since there will be many (unchanged) canvas items which are in the same chunk as the changed canvas items.
.PP
Internally, a canvas uses a low-resolution "chunk matrix" to keep track of all the items in the canvas. A 64x64 chunk matrix is the default for a 1024x1024 pixel canvas, where each chunk collects canvas items in a 16x16 pixel square. This default is also affected by setTiles(). You can tune this default with this function. For example if you have a very large canvas and want to trade off speed for memory then you might set the chunk size to 32 or 64.
.PP
The \fImxclusters\fR argument is the number of rectangular groups of chunks that will be separately drawn. If the canvas has a large number of small, dispersed items, this should be about that number. Our testing suggests that a large number of clusters is almost always best.
.SH "void QCanvas::setAdvancePeriod ( int ms )\fC [virtual]\fR"
Sets the canvas to call advance() every \fIms\fR milliseconds. Any previous setting by setAdvancePeriod() or setUpdatePeriod() is overridden.
.PP
If \fIms\fR is less than 0 advancing will be stopped.
.PP
Example: canvas/main.cpp.
.SH "void QCanvas::setAllChanged ()\fC [virtual]\fR"
Marks the whole canvas as changed. All views of the canvas will be entirely redrawn when update() is called next.
.SH "void QCanvas::setBackgroundColor ( const QColor & c )\fC [virtual]\fR"
Sets the solid background to be the color \fIc\fR.
.PP
See also backgroundColor(), setBackgroundPixmap(), and setTiles().
.SH "void QCanvas::setBackgroundPixmap ( const QPixmap & p )\fC [virtual]\fR"
Sets the solid background to be the pixmap \fIp\fR repeated as necessary to cover the entire canvas.
.PP
See also backgroundPixmap(), setBackgroundColor(), and setTiles().
.SH "void QCanvas::setChanged ( const QRect & area )\fC [virtual]\fR"
Marks \fIarea\fR as changed. This area will be redrawn in all views that are showing it when update() is called next.
.SH "void QCanvas::setDoubleBuffering ( bool y )\fC [virtual]\fR"
If \fIy\fR is TRUE (the default) double-buffering is switched on; otherwise double-buffering is switched off.
.PP
Turning off double-buffering causes the redrawn areas to flicker a bit and also gives a (usually small) performance improvement.
.PP
Example: canvas/canvas.cpp.
.SH "void QCanvas::setTile ( int x, int y, int tilenum )\fC [virtual]\fR"
Sets the tile at (\fIx\fR, \fIy\fR) to use tile number \fItilenum\fR, which is an index into the tile pixmaps. The canvas will update appropriately when update() is next called.
.PP
The images are taken from the pixmap set by setTiles() and are arranged left to right, (and in the case of pixmaps that have multiple rows of tiles, top to bottom), with tile 0 in the top-left corner, tile 1 next to the right, and so on, e.g.
.PP
<center>.nf
.TS
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</center>
.PP
See also tile() and setTiles().
.SH "void QCanvas::setTiles ( QPixmap p, int h, int v, int tilewidth, int tileheight )\fC [virtual]\fR"
Sets the QCanvas to be composed of \fIh\fR tiles horizontally and \fIv\fR tiles vertically. Each tile will be an image \fItilewidth\fR by \fItileheight\fR pixels from pixmap \fIp\fR.
.PP
The pixmap \fIp\fR is a list of tiles, arranged left to right, (and in the case of pixmaps that have multiple rows of tiles, top to bottom), with tile 0 in the top-left corner, tile 1 next to the right, and so on, e.g.
.PP
<center>.nf
.TS
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</center>
.PP
If the canvas is larger than the matrix of tiles, the entire matrix is repeated as necessary to cover the whole canvas. If it is smaller, tiles to the right and bottom are not visible.
.PP
The width and height of \fIp\fR must be a multiple of \fItilewidth\fR and \fItileheight\fR. If they are not the function will do nothing.
.SH "void QCanvas::setUnchanged ( const QRect & area )\fC [virtual]\fR"
Marks \fIarea\fR as \fIunchanged\fR. The area will \fInot\fR be redrawn in the views for the next update(), unless it is marked or changed again before the next call to update().
.SH "void QCanvas::setUpdatePeriod ( int ms )\fC [virtual]\fR"
Sets the canvas to call update() every \fIms\fR milliseconds. Any previous setting by setAdvancePeriod() or setUpdatePeriod() is overridden.
.PP
If \fIms\fR is less than 0 automatic updating will be stopped.
.SH "QSize QCanvas::size () const"
Returns the size of the canvas, in pixels.
.SH "int QCanvas::tile ( int x, int y ) const"
Returns the tile at position (\fIx\fR, \fIy\fR). Initially, all tiles are 0.
.PP
The parameters must be within range, i.e. 0 < \fIx\fR < tilesHorizontally() and 0 < \fIy\fR < tilesVertically().
.PP
See also setTile().
.SH "int QCanvas::tileHeight () const"
Returns the height of each tile.
.SH "int QCanvas::tileWidth () const"
Returns the width of each tile.
.SH "int QCanvas::tilesHorizontally () const"
Returns the number of tiles horizontally.
.SH "int QCanvas::tilesVertically () const"
Returns the number of tiles vertically.
.SH "void QCanvas::update ()\fC [virtual slot]\fR"
Repaints changed areas in all views of the canvas.
.PP
See also advance().
.SH "bool QCanvas::validChunk ( int x, int y ) const"
Returns TRUE if the chunk position (\fIx\fR, \fIy\fR) is on the canvas; otherwise returns FALSE.
.PP
See also onCanvas().
.SH "bool QCanvas::validChunk ( const QPoint & p ) const"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Returns TRUE if the chunk position \fIp\fR is on the canvas; otherwise returns FALSE.
.PP
See also onCanvas().
.SH "int QCanvas::width () const"
Returns the width of the canvas, in pixels.
.PP
Example: canvas/canvas.cpp.

.SH "SEE ALSO"
.BR http://doc.trolltech.com/qcanvas.html
.BR http://www.trolltech.com/faq/tech.html
.SH COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com.  See the
license file included in the distribution for a complete license
statement.
.SH AUTHOR
Generated automatically from the source code.
.SH BUGS
If you find a bug in Qt, please report it as described in
.BR http://doc.trolltech.com/bughowto.html .
Good bug reports help us to help you. Thank you.
.P
The definitive Qt documentation is provided in HTML format; it is
located at $QTDIR/doc/html and can be read using Qt Assistant or with
a web browser. This man page is provided as a convenience for those
users who prefer man pages, although this format is not officially
supported by Trolltech. 
.P
If you find errors in this manual page, please report them to
.BR [e-mail] .
Please include the name of the manual page (qcanvas.3qt) and the Qt
version (3.1.1).