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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QCanvas Class Reference<br><small>[<a href="canvas.html">canvas module</a>]</small></h1>
<p>The QCanvas class provides a 2D area that can contain QCanvasItem objects.
<a href="#details">More...</a>
<p><tt>#include <<a href="qcanvas-h.html">qcanvas.h</a>></tt>
<p>Inherits <a href="qobject.html">QObject</a>.
<p><a href="qcanvas-members.html">List of all member functions.</a>
<h2>Public Members</h2>
<ul>
<li><div class=fn><a href="#QCanvas"><b>QCanvas</b></a> ( QObject * parent = 0, const char * name = 0 )</div></li>
<li><div class=fn><a href="#QCanvas-2"><b>QCanvas</b></a> ( int w, int h )</div></li>
<li><div class=fn><a href="#QCanvas-3"><b>QCanvas</b></a> ( QPixmap p, int h, int v, int tilewidth, int tileheight )</div></li>
<li><div class=fn>virtual <a href="#~QCanvas"><b>~QCanvas</b></a> ()</div></li>
<li><div class=fn>virtual void <a href="#setTiles"><b>setTiles</b></a> ( QPixmap p, int h, int v, int tilewidth, int tileheight )</div></li>
<li><div class=fn>virtual void <a href="#setBackgroundPixmap"><b>setBackgroundPixmap</b></a> ( const QPixmap & p )</div></li>
<li><div class=fn>QPixmap <a href="#backgroundPixmap"><b>backgroundPixmap</b></a> () const</div></li>
<li><div class=fn>virtual void <a href="#setBackgroundColor"><b>setBackgroundColor</b></a> ( const QColor & c )</div></li>
<li><div class=fn>QColor <a href="#backgroundColor"><b>backgroundColor</b></a> () const</div></li>
<li><div class=fn>virtual void <a href="#setTile"><b>setTile</b></a> ( int x, int y, int tilenum )</div></li>
<li><div class=fn>int <a href="#tile"><b>tile</b></a> ( int x, int y ) const</div></li>
<li><div class=fn>int <a href="#tilesHorizontally"><b>tilesHorizontally</b></a> () const</div></li>
<li><div class=fn>int <a href="#tilesVertically"><b>tilesVertically</b></a> () const</div></li>
<li><div class=fn>int <a href="#tileWidth"><b>tileWidth</b></a> () const</div></li>
<li><div class=fn>int <a href="#tileHeight"><b>tileHeight</b></a> () const</div></li>
<li><div class=fn>virtual void <a href="#resize"><b>resize</b></a> ( int w, int h )</div></li>
<li><div class=fn>int <a href="#width"><b>width</b></a> () const</div></li>
<li><div class=fn>int <a href="#height"><b>height</b></a> () const</div></li>
<li><div class=fn>QSize <a href="#size"><b>size</b></a> () const</div></li>
<li><div class=fn>QRect <a href="#rect"><b>rect</b></a> () const</div></li>
<li><div class=fn>bool <a href="#onCanvas"><b>onCanvas</b></a> ( int x, int y ) const</div></li>
<li><div class=fn>bool <a href="#onCanvas-2"><b>onCanvas</b></a> ( const QPoint & p ) const</div></li>
<li><div class=fn>bool <a href="#validChunk"><b>validChunk</b></a> ( int x, int y ) const</div></li>
<li><div class=fn>bool <a href="#validChunk-2"><b>validChunk</b></a> ( const QPoint & p ) const</div></li>
<li><div class=fn>int <a href="#chunkSize"><b>chunkSize</b></a> () const</div></li>
<li><div class=fn>virtual void <a href="#retune"><b>retune</b></a> ( int chunksze, int mxclusters = 100 )</div></li>
<li><div class=fn>virtual void <a href="#setAllChanged"><b>setAllChanged</b></a> ()</div></li>
<li><div class=fn>virtual void <a href="#setChanged"><b>setChanged</b></a> ( const QRect & area )</div></li>
<li><div class=fn>virtual void <a href="#setUnchanged"><b>setUnchanged</b></a> ( const QRect & area )</div></li>
<li><div class=fn>QCanvasItemList <a href="#allItems"><b>allItems</b></a> ()</div></li>
<li><div class=fn>QCanvasItemList <a href="#collisions"><b>collisions</b></a> ( const QPoint & p ) const</div></li>
<li><div class=fn>QCanvasItemList <a href="#collisions-2"><b>collisions</b></a> ( const QRect & r ) const</div></li>
<li><div class=fn>QCanvasItemList <a href="#collisions-3"><b>collisions</b></a> ( const QPointArray & chunklist, const QCanvasItem * item, bool exact ) const</div></li>
<li><div class=fn>void <a href="#drawArea"><b>drawArea</b></a> ( const QRect & clip, QPainter * painter, bool dbuf = FALSE )</div></li>
<li><div class=fn>virtual void <a href="#setAdvancePeriod"><b>setAdvancePeriod</b></a> ( int ms )</div></li>
<li><div class=fn>virtual void <a href="#setUpdatePeriod"><b>setUpdatePeriod</b></a> ( int ms )</div></li>
<li><div class=fn>virtual void <a href="#setDoubleBuffering"><b>setDoubleBuffering</b></a> ( bool y )</div></li>
</ul>
<h2>Public Slots</h2>
<ul>
<li><div class=fn>virtual void <a href="#advance"><b>advance</b></a> ()</div></li>
<li><div class=fn>virtual void <a href="#update"><b>update</b></a> ()</div></li>
</ul>
<h2>Signals</h2>
<ul>
<li><div class=fn>void <a href="#resized"><b>resized</b></a> ()</div></li>
</ul>
<h2>Protected Members</h2>
<ul>
<li><div class=fn>virtual void <a href="#drawBackground"><b>drawBackground</b></a> ( QPainter & painter, const QRect & clip )</div></li>
<li><div class=fn>virtual void <a href="#drawForeground"><b>drawForeground</b></a> ( QPainter & painter, const QRect & clip )</div></li>
</ul>
<hr><a name="details"></a><h2>Detailed Description</h2>
The QCanvas class provides a 2D area that can contain <a href="qcanvasitem.html">QCanvasItem</a> objects.
<p>
<p> The QCanvas class manages its 2D graphic area and all the canvas items
the area contains. The canvas is displayed on screen with a <a href="qcanvasview.html">QCanvasView</a>
widget. Multiple QCanvasView widgets may be associated with a
canvas to provide multiple views of the same canvas.
<p> The canvas is optimized for large numbers of items. Qt provides a rich
set of canvas item classes, e.g. <a href="qcanvasellipse.html">QCanvasEllipse</a>, <a href="qcanvasline.html">QCanvasLine</a>,
<a href="qcanvaspolygon.html">QCanvasPolygon</a>, <a href="qcanvaspolygonalitem.html">QCanvasPolygonalItem</a>, <a href="qcanvasrectangle.html">QCanvasRectangle</a>, <a href="qcanvasspline.html">QCanvasSpline</a>,
<a href="qcanvassprite.html">QCanvasSprite</a> and <a href="qcanvastext.html">QCanvasText</a>. You can subclass to create your own
canvas items; QCanvasPolygonalItem is the most common base class used
for this purpose.
<p> Although a canvas may appear to be similar to a widget with child
widgets, there are several notable differences:
<p> <ul>
<li> Canvas items are usually far faster to manipulate and redraw than
child widgets, with the speed advantage becoming especially great when
there are <em>many</em> canvas items and non-rectangular items. In most
situations canvas items are also a lot more memory efficient than child
widgets.
<p> <li> It's easy to detect overlapping items (collision detection).
<p> <li> The canvas can be larger than a widget. A million-by-million canvas
is perfectly possible. Although a widget might be very inefficient at
this size and some window systems might not support it at all, QCanvas
scales well. Even with a billion pixels and a million items finding a
particular canvas item, detecting collisions, etc. is still fast.
<p> <li> Two or more <a href="qcanvasview.html">QCanvasView</a> objects can view the same canvas.
<p> <li> An arbitrary transformation matrix can be set on each QCanvasView
which makes it easy to zoom, rotate or sheer the viewed canvas.
<p> <li> Widgets provide a lot more functionality, such as input (<a href="qkeyevent.html">QKeyEvent</a>,
<a href="qmouseevent.html">QMouseEvent</a> etc.) and layout management (<a href="qgridlayout.html">QGridLayout</a> etc.).
<p> </ul>
<p> A canvas consists of a background, a number of canvas items organized by
x, y and z coordinates, and a foreground. A canvas item's z coordinate
may be treated as a layer number -- canvas items with higher z
coordinate will appear in front of canvas items with a lower z
coordinate.
<p> The background is white by default, but can be set to a different color
using <a href="#setBackgroundColor">setBackgroundColor</a>(), or to a repeated pixmap using
<a href="#setBackgroundPixmap">setBackgroundPixmap</a>() or to a mosaic of smaller pixmaps using
<a href="#setTiles">setTiles</a>(). Individual tiles can be set with <a href="#setTile">setTile</a>(). As usual, there
are corresponding get functions like <a href="#backgroundColor">backgroundColor</a>().
<p> Note that QCanvas does not inherit from <a href="qwidget.html">QWidget</a>, even though it has some
functions which provide the same functionality as those in QWidget. One
of these is setBackgroundPixmap(); some others are <a href="#resize">resize</a>(), <a href="#size">size</a>(),
<a href="#width">width</a>() and <a href="#height">height</a>(). <a href="qcanvasview.html">QCanvasView</a> is the widget used to display a
canvas on the screen.
<p> Canvas items are added to a canvas by constructing them and passing the
canvas to the canvas item's constructor. An item can be moved to a
different canvas using <a href="qcanvasitem.html#setCanvas">QCanvasItem::setCanvas</a>().
<p> Canvas items are movable (and in the case of QCanvasSprites, animated)
objects that inherit <a href="qcanvasitem.html">QCanvasItem</a>. Each canvas item has a position on the
canvas (x, y coordinates) and a height (z coordinate), all of which are
held as floating-point numbers. Moving canvas items also have x and y
velocities. It's possible for a canvas item to be outside the canvas
(for example <a href="qcanvasitem.html#x">QCanvasItem::x</a>() is greater than width()). When a canvas
item is off the canvas, <a href="#onCanvas">onCanvas</a>() returns FALSE and the canvas
disregards the item. (Canvas items off the canvas do not slow down any
common operations on the canvas.)
<p> Canvas items can be moved with <a href="qcanvasitem.html#move">QCanvasItem::move</a>(). The <a href="#advance">advance</a>()
function moves all <a href="qcanvasitem.html#animated">QCanvasItem::animated</a>() canvas items and
<a href="#setAdvancePeriod">setAdvancePeriod</a>() makes QCanvas move them by itself on a periodic
basis. In the context of the QCanvas classes, to `animate' a canvas item
is to set it in motion, i.e. using <a href="qcanvasitem.html#setVelocity">QCanvasItem::setVelocity</a>(). Animation
of a canvas item itself, i.e. items which change over time, is enabled
by calling <a href="qcanvassprite.html#setFrameAnimation">QCanvasSprite::setFrameAnimation</a>(), or more generally by
subclassing and reimplementing <a href="qcanvasitem.html#advance">QCanvasItem::advance</a>(). To detect collisions
use one of the <a href="qcanvasitem.html#collisions">QCanvasItem::collisions</a>() functions.
<p> The changed parts of the canvas are redrawn (if they are visible in a
canvas view) whenever <a href="#update">update</a>() is called. You can either call update()
manually after having changed the contents of the canvas, or force
periodic updates using <a href="#setUpdatePeriod">setUpdatePeriod</a>(). If you have moving objects on
the canvas, you need to call <a href="#advance">advance</a>() every time the objects should
move one step further. Periodic calls to advance() can be forced using
<a href="#setAdvancePeriod">setAdvancePeriod</a>(). The advance() function will call
QCanvasItem::advance() on every item that is <a href="qcanvasitem.html#animated">QCanvasItem::animated</a>() and
trigger an update of the affected areas afterwards. (A canvas item that
is `animated' is simply a canvas item that is in motion.)
<p> QCanvas organizes its canvas items into <em>chunks</em> - areas on the canvas
that are used to speed up most operations. Many operations start by
eliminating most chunks (i.e. those which haven't changed) and then
process only the canvas items that are in the few interesting (i.e.
changed) chunks. A valid chunk, <a href="#validChunk">validChunk</a>(), is one
which is on the canvas.
<p> The chunk size is a key factor to QCanvas's speed: if there are too many
chunks, the speed benefit of grouping canvas items into chunks is
reduced. If the chunks are too large, it takes too long to process each
one. The QCanvas constructor picks a hopefully suitable size, but you
can call <a href="#retune">retune</a>() to change it at any time. The <a href="#chunkSize">chunkSize</a>() function
returns the current chunk size.
<p> The canvas items always make sure they're in the right chunks; all you
need to make sure of is that the canvas uses the right chunk size. A
good rule of thumb is that the size should be a bit smaller than the
average canvas item size. If you have moving objects, the chunk size
should be a bit smaller than the average size of the moving items.
<p> The foreground is normally nothing, but if you reimplement
<a href="#drawForeground">drawForeground</a>(), you can draw things in front of all canvas items.
<p> Areas can be set as changed with <a href="#setChanged">setChanged</a>() and set unchanged with
<a href="#setUnchanged">setUnchanged</a>(). The entire canvas can be set as changed with
<a href="#setAllChanged">setAllChanged</a>(). A list of all the items on the canvas is returned by
<a href="#allItems">allItems</a>().
<p> An area can be copied (painted) to a <a href="qpainter.html">QPainter</a> with <a href="#drawArea">drawArea</a>().
<p> If the canvas is resized it emits the <a href="#resized">resized</a>() signal.
<p> The examples/canvas application and the 2D graphics page of the
examples/demo application demonstrate many of QCanvas's facilities.
<p> <p>See also <a href="qcanvasview.html">QCanvasView</a>, <a href="qcanvasitem.html">QCanvasItem</a>, <a href="abstractwidgets.html">Abstract Widget Classes</a>, <a href="graphics.html">Graphics Classes</a> and <a href="images.html">Image Processing Classes</a>.
<hr><h2>Member Function Documentation</h2>
<h3 class=fn><a name="QCanvas"></a>QCanvas::QCanvas ( <a href="qobject.html">QObject</a> * parent = 0, const char * name = 0 )
</h3> Create a QCanvas with no size. <em>parent</em> and <em>name</em> have the
usual <a href="qobject.html">QObject</a> meaning.
<p> You <em>must</em> call <a href="#resize">resize</a>() at some time after creation to be able to
use the canvas.
<h3 class=fn><a name="QCanvas-2"></a>QCanvas::QCanvas ( int w, int h )
</h3>
Constructs a QCanvas that is <em>w</em> pixels wide and <em>h</em> pixels high.
<h3 class=fn><a name="QCanvas-3"></a>QCanvas::QCanvas ( <a href="qpixmap.html">QPixmap</a> p, int h, int v, int tilewidth, int tileheight )
</h3>
Constructs a QCanvas which will be composed of
<em>h</em> tiles horizontally and <em>v</em> tiles vertically. Each tile
will be an image <em>tilewidth</em> by <em>tileheight</em> pixels taken from
pixmap <em>p</em>.
<p> The pixmap <em>p</em> 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.
<p> <center><table cellpadding="4" cellspacing="2" border="0">
<tr bgcolor="#f0f0f0"> <td valign="top">0 <td valign="top">1 <td valign="top">2 <td valign="top">3
<tr bgcolor="#d0d0d0"> <td valign="top">4 <td valign="top">5 <td valign="top">6 <td valign="top">7
</table></center>
<p> 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.
<p> <p>See also <a href="#setTiles">setTiles</a>().
<h3 class=fn><a name="~QCanvas"></a>QCanvas::~QCanvas ()<tt> [virtual]</tt>
</h3>
Destroys the canvas and all the canvas's canvas items.
<h3 class=fn>void <a name="advance"></a>QCanvas::advance ()<tt> [virtual slot]</tt>
</h3> Moves all <a href="qcanvasitem.html#animated">QCanvasItem::animated</a>() 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().)
<p> The advance is done in two phases. In phase 0, the
<a href="qcanvasitem.html#advance">QCanvasItem::advance</a>() 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", though no <a href="qcanvasitem.html">QCanvasItem</a> subclasses
supplied with Qt do anything interesting in phase 0.
<p> The canvas can be configured to call this function periodically with
<a href="#setAdvancePeriod">setAdvancePeriod</a>().
<p> <p>See also <a href="#update">update</a>().
<h3 class=fn><a href="qcanvasitemlist.html">QCanvasItemList</a> <a name="allItems"></a>QCanvas::allItems ()
</h3>
Returns a list of all items in the canvas.
<h3 class=fn><a href="qcolor.html">QColor</a> <a name="backgroundColor"></a>QCanvas::backgroundColor () const
</h3>
Returns the color set by <a href="#setBackgroundColor">setBackgroundColor</a>().
By default, this is white.
<p> Note that this function is not a reimplementation
of <a href="qwidget.html#backgroundColor">QWidget::backgroundColor</a>() (QCanvas is not a subclass
of <a href="qwidget.html">QWidget</a>), but all QCanvasViews that are viewing the
canvas will set their backgrounds to this color.
<p> <p>See also <a href="#setBackgroundColor">setBackgroundColor</a>() and <a href="#backgroundPixmap">backgroundPixmap</a>().
<h3 class=fn><a href="qpixmap.html">QPixmap</a> <a name="backgroundPixmap"></a>QCanvas::backgroundPixmap () const
</h3>
Returns the pixmap set by <a href="#setBackgroundPixmap">setBackgroundPixmap</a>(). By default,
this is a null pixmap.
<p> <p>See also <a href="#setBackgroundPixmap">setBackgroundPixmap</a>() and <a href="#backgroundColor">backgroundColor</a>().
<h3 class=fn>int <a name="chunkSize"></a>QCanvas::chunkSize () const
</h3>
Returns the chunk size of the canvas.
<p>See also <a href="#retune">retune</a>().
<h3 class=fn><a href="qcanvasitemlist.html">QCanvasItemList</a> <a name="collisions"></a>QCanvas::collisions ( const <a href="qpoint.html">QPoint</a> & p ) const
</h3>
Returns a list of canvas items that intersect with the point <em>p</em>.
The list is ordered by z coordinates, from highest z coordinate
(front-most item) to lowest z coordinate (rear-most item).
<h3 class=fn><a href="qcanvasitemlist.html">QCanvasItemList</a> <a name="collisions-2"></a>QCanvas::collisions ( const <a href="qrect.html">QRect</a> & r ) const
</h3>
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
<p> Returns a list of items which intersect with the rectangle <em>r</em>.
The list is ordered by z coordinates, from highest z coordinate
(front-most item) to lowest z coordinate (rear-most item).
<h3 class=fn><a href="qcanvasitemlist.html">QCanvasItemList</a> <a name="collisions-3"></a>QCanvas::collisions ( const <a href="qpointarray.html">QPointArray</a> & chunklist, const <a href="qcanvasitem.html">QCanvasItem</a> * item, bool exact ) const
</h3>
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
<p> Returns a list of canvas items which intersect with the chunks listed
in <em>chunklist</em>, excluding <em>item</em>. If <em>exact</em> is TRUE, only only
those which actually <a href="qcanvasitem.html#collidesWith">QCanvasItem::collidesWith</a>() <em>item</em> are returned,
otherwise canvas items are included just for being in the chunks.
<p> This is a utility function mainly used to implement the simpler
<a href="qcanvasitem.html#collisions">QCanvasItem::collisions</a>() function.
<h3 class=fn>void <a name="drawArea"></a>QCanvas::drawArea ( const <a href="qrect.html">QRect</a> & clip, <a href="qpainter.html">QPainter</a> * painter, bool dbuf = FALSE )
</h3>
Paints all canvas items that are in the area <em>clip</em> to <em>painter</em>,
using double-buffering if <em>dbuf</em> is TRUE.
<p> eg. to print the canvas to a printer:
<p> <pre>
<a href="qprinter.html">QPrinter</a> pr;
if ( pr.<a href="qprinter.html#setup">setup</a>() ) {
<a href="qpainter.html">QPainter</a> p(&pr);
canvas.drawArea( canvas.rect(), &p );
}
</pre>
<p>Example: <a href="canvas-example.html#x2508">canvas/canvas.cpp</a>.
<h3 class=fn>void <a name="drawBackground"></a>QCanvas::drawBackground ( <a href="qpainter.html">QPainter</a> & painter, const <a href="qrect.html">QRect</a> & clip )<tt> [virtual protected]</tt>
</h3>
This virtual function is called for all updates of the canvas.
It renders any background graphics using the painter <em>painter</em>, in the
area <em>clip</em>. If the canvas has a background
pixmap or a tiled background, that graphic is used, otherwise the
canvas is cleared using the background color.
<p> If the graphics for an area change, you must explicitly call
<a href="#setChanged">setChanged</a>(const <a href="qrect.html">QRect</a>&) for the result to be visible when <a href="#update">update</a>()
is next called.
<p> <p>See also <a href="#setBackgroundColor">setBackgroundColor</a>(), <a href="#setBackgroundPixmap">setBackgroundPixmap</a>() and <a href="#setTiles">setTiles</a>().
<h3 class=fn>void <a name="drawForeground"></a>QCanvas::drawForeground ( <a href="qpainter.html">QPainter</a> & painter, const <a href="qrect.html">QRect</a> & clip )<tt> [virtual protected]</tt>
</h3>
This virtual function is called for all updates of the canvas.
It renders any foreground graphics using the painter <em>painter</em>, in
the area <em>clip</em>.
<p> If the graphics for an area change, you must explicitly call
<a href="#setChanged">setChanged</a>(const <a href="qrect.html">QRect</a>&) for the result to be visible when <a href="#update">update</a>()
is next called.
<p> The default is to draw nothing.
<h3 class=fn>int <a name="height"></a>QCanvas::height () const
</h3>
Returns the height of the canvas, in pixels.
<p>Example: <a href="canvas-example.html#x2509">canvas/canvas.cpp</a>.
<h3 class=fn>bool <a name="onCanvas"></a>QCanvas::onCanvas ( int x, int y ) const
</h3>
Returns TRUE if the pixel position (<em>x</em>, <em>y</em>) is on the canvas;
otherwise returns FALSE.
<h3 class=fn>bool <a name="onCanvas-2"></a>QCanvas::onCanvas ( const <a href="qpoint.html">QPoint</a> & p ) const
</h3>
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
<p> Returns TRUE if the pixel position <em>p</em> is on the canvas;
otherwise returns FALSE.
<h3 class=fn><a href="qrect.html">QRect</a> <a name="rect"></a>QCanvas::rect () const
</h3>
Returns a rectangle the size of the canvas.
<h3 class=fn>void <a name="resize"></a>QCanvas::resize ( int w, int h )<tt> [virtual]</tt>
</h3>
Changes the size of the canvas to have a width of <em>w</em> and a height of <em>h</em>.
This is a slow operation.
<p>Example: <a href="canvas-example.html#x2510">canvas/canvas.cpp</a>.
<h3 class=fn>void <a name="resized"></a>QCanvas::resized ()<tt> [signal]</tt>
</h3>
<p> This signal is emitted whenever the canvas is resized. Each <a href="qcanvasview.html">QCanvasView</a>
connects to this signal to keep the scrollview size correct.
<h3 class=fn>void <a name="retune"></a>QCanvas::retune ( int chunksze, int mxclusters = 100 )<tt> [virtual]</tt>
</h3> Change the efficiency tuning parameters to <em>mxclusters</em> clusters,
each of size <em>chunksze</em>. This is a slow operation if there are many
objects on the canvas.
<p> The canvas is divided into chunks which are rectangular areas of the canvas
<em>chunksze</em> wide by <em>chunksze</em> 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.
<p> 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
<a href="#setTiles">setTiles</a>(). 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.
<p> The <em>mxclusters</em> 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.
<p>
<h3 class=fn>void <a name="setAdvancePeriod"></a>QCanvas::setAdvancePeriod ( int ms )<tt> [virtual]</tt>
</h3>
Sets the canvas to call <a href="#advance">advance</a>() every <em>ms</em> milliseconds. Any
previous setting by <a href="#setAdvancePeriod">setAdvancePeriod</a>() or <a href="#setUpdatePeriod">setUpdatePeriod</a>() is
overridden.
<p> If <em>ms</em> is less than 0 advancing will be stopped.
<p>Example: <a href="canvas-example.html#x2563">canvas/main.cpp</a>.
<h3 class=fn>void <a name="setAllChanged"></a>QCanvas::setAllChanged ()<tt> [virtual]</tt>
</h3>
Marks the whole canvas as changed.
All views of the canvas will be entirely redrawn when
<a href="#update">update</a>() is next called.
<h3 class=fn>void <a name="setBackgroundColor"></a>QCanvas::setBackgroundColor ( const <a href="qcolor.html">QColor</a> & c )<tt> [virtual]</tt>
</h3>
Sets the solid background to be the color <em>c</em>.
<p>See also <a href="#backgroundColor">backgroundColor</a>(), <a href="#setBackgroundPixmap">setBackgroundPixmap</a>() and <a href="#setTiles">setTiles</a>().
<h3 class=fn>void <a name="setBackgroundPixmap"></a>QCanvas::setBackgroundPixmap ( const <a href="qpixmap.html">QPixmap</a> & p )<tt> [virtual]</tt>
</h3>
Sets the solid background to be the pixmap <em>p</em> repeated as
necessary to cover the entire canvas.
<p> <p>See also <a href="#backgroundPixmap">backgroundPixmap</a>(), <a href="#setBackgroundColor">setBackgroundColor</a>() and <a href="#setTiles">setTiles</a>().
<h3 class=fn>void <a name="setChanged"></a>QCanvas::setChanged ( const <a href="qrect.html">QRect</a> & area )<tt> [virtual]</tt>
</h3>
Marks <em>area</em> as changed. This area will be redrawn in all views
showing it when <a href="#update">update</a>() is next called.
<h3 class=fn>void <a name="setDoubleBuffering"></a>QCanvas::setDoubleBuffering ( bool y )<tt> [virtual]</tt>
</h3>
If <em>y</em> is TRUE (the default) double-buffering is switched on;
otherwise double-buffering is switched off.
<p> Turning off double-buffering causes the redrawn areas to flicker a
bit and also gives a (usually small) performance improvement.
<p>Example: <a href="canvas-example.html#x2511">canvas/canvas.cpp</a>.
<h3 class=fn>void <a name="setTile"></a>QCanvas::setTile ( int x, int y, int tilenum )<tt> [virtual]</tt>
</h3> Sets the tile at (<em>x</em>, <em>y</em>) to use tile number <em>tilenum</em>,
which is an index into the tile pixmaps. The canvas will update
appropriately when <a href="#update">update</a>() is next called.
<p> The images are taken from the pixmap set by <a href="#setTiles">setTiles</a>() 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.
<p> <center><table cellpadding="4" cellspacing="2" border="0">
<tr bgcolor="#f0f0f0"> <td valign="top">0 <td valign="top">1 <td valign="top">2 <td valign="top">3
<tr bgcolor="#d0d0d0"> <td valign="top">4 <td valign="top">5 <td valign="top">6 <td valign="top">7
</table></center>
<p> <p>See also <a href="#tile">tile</a>() and <a href="#setTiles">setTiles</a>().
<h3 class=fn>void <a name="setTiles"></a>QCanvas::setTiles ( <a href="qpixmap.html">QPixmap</a> p, int h, int v, int tilewidth, int tileheight )<tt> [virtual]</tt>
</h3> Sets the QCanvas to be composed of <em>h</em> tiles horizontally and <em>v</em> tiles vertically. Each tile will be an image <em>tilewidth</em> by <em>tileheight</em> pixels from pixmap <em>p</em>.
<p> The pixmap <em>p</em> 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.
<p> <center><table cellpadding="4" cellspacing="2" border="0">
<tr bgcolor="#f0f0f0"> <td valign="top">0 <td valign="top">1 <td valign="top">2 <td valign="top">3
<tr bgcolor="#d0d0d0"> <td valign="top">4 <td valign="top">5 <td valign="top">6 <td valign="top">7
</table></center>
<p> 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.
<p> The width and height of <em>p</em> must be a multiple of <em>tilewidth</em> and
<em>tileheight</em>. If they are not the function will return without
performing any action.
<h3 class=fn>void <a name="setUnchanged"></a>QCanvas::setUnchanged ( const <a href="qrect.html">QRect</a> & area )<tt> [virtual]</tt>
</h3>
Marks <em>area</em> as <em>unchanged</em>. The area will <em>not</em> be redrawn in the
views for the next <a href="#update">update</a>(), unless it is marked and changed again
before the next call to update().
<h3 class=fn>void <a name="setUpdatePeriod"></a>QCanvas::setUpdatePeriod ( int ms )<tt> [virtual]</tt>
</h3>
Sets the canvas to call <a href="#update">update</a>() every <em>ms</em> milliseconds. Any
previous setting by <a href="#setAdvancePeriod">setAdvancePeriod</a>() or <a href="#setUpdatePeriod">setUpdatePeriod</a>() is
cancelled.
<p> If <em>ms</em> is less than 0 automatic updating will be stopped.
<h3 class=fn><a href="qsize.html">QSize</a> <a name="size"></a>QCanvas::size () const
</h3>
Returns the size of the canvas, in pixels.
<h3 class=fn>int <a name="tile"></a>QCanvas::tile ( int x, int y ) const
</h3>
<p> Returns the tile at position (<em>x</em>, <em>y</em>). Initially, all tiles are 0.
<p> The parameters must be within range, i.e.
0 < <em>x</em> < <a href="#tilesHorizontally">tilesHorizontally</a>() and
0 < <em>y</em> < <a href="#tilesVertically">tilesVertically</a>().
<p> <p>See also <a href="#setTile">setTile</a>().
<h3 class=fn>int <a name="tileHeight"></a>QCanvas::tileHeight () const
</h3>
Returns the height of each tile.
<h3 class=fn>int <a name="tileWidth"></a>QCanvas::tileWidth () const
</h3>
Returns the width of each tile.
<h3 class=fn>int <a name="tilesHorizontally"></a>QCanvas::tilesHorizontally () const
</h3>
Returns the number of tiles horizontally.
<h3 class=fn>int <a name="tilesVertically"></a>QCanvas::tilesVertically () const
</h3>
Returns the number of tiles vertically.
<h3 class=fn>void <a name="update"></a>QCanvas::update ()<tt> [virtual slot]</tt>
</h3>
Repaints changed areas in all views of the canvas.
<p> <p>See also <a href="#advance">advance</a>().
<h3 class=fn>bool <a name="validChunk"></a>QCanvas::validChunk ( int x, int y ) const
</h3>
Returns TRUE if the chunk position (<em>x</em>, <em>y</em>) is on the canvas;
otherwise returns FALSE.
<h3 class=fn>bool <a name="validChunk-2"></a>QCanvas::validChunk ( const <a href="qpoint.html">QPoint</a> & p ) const
</h3>
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
<p> Returns whether the chunk position <em>p</em> is on the canvas.
<h3 class=fn>int <a name="width"></a>QCanvas::width () const
</h3>
Returns the width of the canvas, in pixels.
<p>Example: <a href="canvas-example.html#x2512">canvas/canvas.cpp</a>.
<!-- eof -->
<hr><p>
This file is part of the <a href="index.html">Qt toolkit</a>.
Copyright © 1995-2001
<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
<table width=100% cellspacing=0 border=0><tr>
<td>Copyright © 2001
<a href="http://www.trolltech.com">Trolltech</a><td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a>
<td align=right><div align=right>Qt version 3.0.2</div>
</table></div></address></body>
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