QCanvas(3qt)QCanvas(3qt)NAMEQCanvas - 2D graphic area upon which
#include <qcanvas.h>
Inherits QObject.
Public Members
QCanvas ( QObject * parent = 0, const char * name = 0 )
QCanvas ( int w, int h )
QCanvas ( QPixmap p, int h, int v, int tilewidth, int
tileheight )
virtual ~QCanvas ()
virtual void setTiles ( QPixmap tiles, int h, int v, int
tilewidth, int tileheight )
virtual void setBackgroundPixmap ( const QPixmap & p )
QPixmap backgroundPixmap () const
virtual void setBackgroundColor ( const QColor & c )
QColor backgroundColor () const
virtual void setTile ( int x, int y, int tilenum )
int tile ( int x, int y ) const
int tilesHorizontally () const
int tilesVertically () const
int tileWidth () const
int tileHeight () const
virtual void resize ( int width, int height )
int width () const
int height () const
QSize size () const
bool onCanvas ( int x, int y ) const
bool onCanvas ( const QPoint & p ) const
bool validChunk ( int x, int y ) const
bool validChunk ( const QPoint & p ) const
int chunkSize () const
virtual void retune ( int chunksize, int maxclusters=100 )
bool sameChunk ( int x1, int y1, int x2, int y2 ) const
(internal)
virtual void setChangedChunk ( int i, int j ) (internal)
virtual void setChangedChunkContaining ( int x, int y )
(internal)
virtual void setAllChanged ()
virtual void setChanged ( const QRect & inarea )
void addItemToChunk ( QCanvasItem *, int i, int j )
(internal)
void removeItemFromChunk ( QCanvasItem *, int i, int j )
(internal)
void addItemToChunkContaining ( QCanvasItem *, int x, int
y ) (internal)
void removeItemFromChunkContaining ( QCanvasItem *, int x,
int y ) (internal)
QCanvasItemList allItems ()
QCanvasItemList collisions ( const QPoint & ) const
QCanvasItemList collisions ( const QRect & ) const
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QCanvas(3qt)QCanvas(3qt)
QCanvasItemList collisions ( const QPointArray & pa, const
QCanvasItem * item, bool exact ) const
virtual void addView ( QCanvasView * ) (internal)
virtual void removeView ( QCanvasView * ) (internal)
void drawArea ( const QRect &, QPainter * p=0, bool
double_buffer=TRUE ) (internal)
virtual void addItem ( QCanvasItem * ) (internal)
virtual void addAnimation ( QCanvasItem * ) (internal)
virtual void removeItem ( QCanvasItem * ) (internal)
virtual void removeAnimation ( QCanvasItem * ) (internal)
virtual void setAdvancePeriod ( int ms )
virtual void setUpdatePeriod ( int ms )
virtual void setDoubleBuffering ( bool y )
Public Slots
virtual void advance ()
virtual void update ()
Signals
void resized ()
Protected Members
virtual void drawBackground ( QPainter &, const QRect &
area )
virtual void drawForeground ( QPainter &, const QRect &
area )
DESCRIPTION
The QCanvas class is a 2D graphic area upon which
QCanvasItem objects exist.
A QCanvas contains any number of QCanvasItem subclassed
objects and has any number of QCanvasView widgets
observing some part of the canvas.
A canvas containing many items is different to a widgets
containing many subwidgets in the following ways:
Items are drawn much faster than widgets, especially when
non- rectangular.
Items use less memory than widgets.
You can do efficient item-to-item hit tests ("collision
detection") with items in a canvas.
Finding items in an area is efficient.
You can have multiple views of a canvas.
Widgets of course offer richer functionality, such as
hierarchies, events, layout, etc.
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QCanvas(3qt)QCanvas(3qt)Drawing
A canvas has a solid background and a foreground. By
default, the canvas will have a white background, which
can be changed with setBackgroundColor(). If you want an
image, use setBackgroundPixmap(). A third option is to use
tiles, where the canvas background is a matrix of small
images all the same size, each chosen from a defined
larger pixmap. See setTiles().
On top of the background are objects of QCanvasItems
subclasses. Each item has a Z-height (see
QCanvasItem::z()), with the lower-Z items on the
background and higher-Z items on top of them.
Above everything in the canvas is the foreground, as
defined by the drawForeground() function. By default this
function draws nothing.
Changes to the items on the canvas are refreshed to the
views whenever update() is called, including creation of
new items, movement of item, change of shape, change of
visibility, and destruction.
Note that like QWidgets, QCanvasItems are always hidden
when they are created, so you must show() them some time
after creating them if you wish them to be visible.
AnimationQCanvas has some built-in animation features. If you call
QCanvasItem::setVelocity() on an item, it will move
forward whenever advance() is call. The advance() function
also calls update(), so you only need to call one or the
other. If no items have a velocity, then advance() is the
same as update().
You can have advance() or update() called automatically
with setAdvancePeriod() or setUpdatePeriod() respectively.
Collision Detection
Items on the canvas can be tested for collisions with
these functions, each of which returns a list of items
which match the hit, sorted from top to bottom (ie. by
decreasing QCanvasItem::z() value).
collisions(QPoint) - items which will collide with a
point.
collisions(QRect) - items which will collide with a
rectangle.
You can also test for item-to-item collisions with
QCanvasItem::collisions().
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QCanvas(3qt)QCanvas(3qt)MEMBER FUNCTION DOCUMENTATIONQCanvas::QCanvas ( QObject * parent = 0, const char * name = 0 )
Create a QCanvas with no size. You will want to call
resize(int,int) at some time after creation.
QCanvas::QCanvas ( QPixmap p, int h, int v, int tilewidth, int
tileheight )
Constructs a QCanvas which will be composed of h tiles
horizontally and v tiles vertically. Each tile will be an
image tilewidth by tileheight pixels from pixmap p.
The pixmap p is a list of tiles, arranged left to right,
top to bottom, with tile 0 in the top-left corner, tile 1
next to the right, and so on.
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.
QCanvas::QCanvas ( int w, int h )
Constructs a QCanvas with that is w pixels wide and h
pixels high.
QCanvas::~QCanvas () [virtual]
Destructs the canvas. Does also destroy all items on the
canvas.
void QCanvas::advance () [virtual slot]
Advances the animation of items on the canvas and
refreshes all changes to all views of the canvas.
The advance is done in two phases. In phase 0, the
QCanvasItem:advance() function of each animated item is
called with paramater 0. Then all items are called again,
with parameter 1. In phase 0, the 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 items should change
positions, ignoring any other items on the canvas. This
two-phase approach allows for considerations of
"fairness", though no QCanvasItem subclasses supplied with
Qt do anything interesting in phase 0.
The canvas can be configured to call this function
periodically with setAdvancePeriod().
See also update().
QCanvasItemList QCanvas::allItems ()
Returns a list of all items in the canvas.
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QCanvas(3qt)QCanvas(3qt)QColor QCanvas::backgroundColor () const
Returns the color set by setBackgroundColor(). By default,
this is white.
Note that 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
See also setBackgroundColor() and backgroundPixmap().
QPixmap QCanvas::backgroundPixmap () const
Returns the pixmap set by setBackgroundPixmap(). By
default, this is a null pixmap.
See also setBackgroundPixmap() and backgroundColor().
int QCanvas::chunkSize () const
Returns the chunk size of the canvas as set at
construction.
See also retune().
QCanvasItemList QCanvas::collisions ( const QPoint & p ) const
Returns a list of items which intersect with the point p,
sorted from shallowest to deepest.
QCanvasItemList QCanvas::collisions ( const QPointArray &
chunklist, const QCanvasItem * item, bool exact ) const
Returns a list of items which intersect with the chunks
listed in chunklist, excluding item. If exact is TRUE,
only only those which actually QCanvasItem::collidesWith()
item are returned, otherwise items are included just for
being in the chunks.
This is a utility function mainly used to implement the
simpler QCanvasItem::collisions() function.
QCanvasItemList QCanvas::collisions ( const QRect & r ) const
Returns a list of items which intersect with the rectangle
r, sorted from shallowest to deepest.
void QCanvas::drawBackground ( QPainter & painter, const QRect &
clip ) [virtual protected]
This virtual function is called for all updates of the
QCanvas. It renders any background graphics. If the canvas
has a background pixmap or a tiled background, that
graphic is used, otherwise the canvas is cleared in the
background color.
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.
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QCanvas(3qt)QCanvas(3qt)
See also setBackgroundColor(), setBackgroundPixmap() and
setTiles().
void QCanvas::drawForeground ( QPainter & painter, const QRect &
clip ) [virtual protected]
This virtual function is called for all updates of the
QCanvas. It renders any foreground graphics.
The same warnings regarding change apply to this method as
for drawBackground().
The default is to draw nothing.
int QCanvas::height () const
Returns the height of the canvas, in pixels.
bool QCanvas::onCanvas ( const QPoint & p ) const
Returns whether the pixel position p is on the canvas.
bool QCanvas::onCanvas ( int x, int y ) const
Returns whether the pixel position (x, y) is on the
canvas.
void QCanvas::resize ( int w, int h ) [virtual]
Changes the size of the QCanvas. This is a slow operation.
void QCanvas::resized () [signal]
This signal is emitted whenever the canvas is resized.
Each QCanvasView connects to this signal to keep the
scrollview size correct.
void QCanvas::retune ( int chunksze, int mxclusters=100 )
[virtual]
Change the efficiency tuning parameters to mxclusters
clusters, each of size chunksze (square). This is a slow
operation if you have many objects on the canvas.
Internally, a canvas uses a low-resolution "chunk matrix"
to keep track of all the items in the canvas. In Qt 2.2,
the default for a 1024x1024 pixel canvas is to have a
64x64 chunk matrix, where each of those chunks collects
items in a 16x16 pixel square.
This default is also affected by setTiles(). You can tune
this default by using retune(), 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.
chunksze is the size of square chunk used to break up the
QCanvas into area to be considered for redrawing. It
should be about the average size of items in the QCanvas.
Chunks too small increase the amount of calculation
required when drawing. Chunks too large increase the
amount of drawing that is needed.
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QCanvas(3qt)QCanvas(3qt)
mxclusters is the number of rectangular groups of chunks
that will be separately drawn. If the QCanvas has a large
number of small, dispersed items, this should be about
that number. The more clusters the slower the redraw, but
also the bigger clusters are the slower the redraw, so a
balance is needed. Testing indicates that a large number
of clusters is almost always best.
void QCanvas::setAdvancePeriod ( int ms ) [virtual]
Sets the canvas to call advance() every ms milliseconds.
Any previous setting by setAdvancePeriod() or
setUpdatePeriod() is cancelled.
void QCanvas::setAllChanged () [virtual]
Sets all views of the canvas to be entirely redrawn when
update() is next called.
void QCanvas::setBackgroundColor ( const QColor & c ) [virtual]
Sets the solid background to be the color c.
See also backgroundColor(), setBackgroundPixmap() and
setTiles().
void QCanvas::setBackgroundPixmap ( const QPixmap & p ) [virtual]
Sets the solid background to be p, repeated as necessary
to cover the entire canvas.
See also backgroundPixmap(), setBackgroundColor() and
setTiles().
void QCanvas::setChanged ( const QRect & area ) [virtual]
Sets all views of area to be entirely redrawn when
update() is next called.
void QCanvas::setDoubleBuffering ( bool y ) [virtual]
Turns double-buffering on if y is TRUE, or off if it is
FALSE. The default is to use double-buffering.
Turning off double-buffering casuses the redrawn areas to
flicker a bit. This can help understand the the
optimizations made by QCanvas and also gives a (usually
small) performance improvement.
void QCanvas::setTile ( int x, int y, int tilenum ) [virtual]
Sets the tile at (x, y) to use tile number tilenum, which
is an index into the tile pixmaps. The canvas will update
appropriately when update() is next called.
The images are taken from the pixmap set by setTiles() and
are arranged in the pixmap left to right, top to bottom,
with tile 0 in the top-left corner, tile 1 next to the
right, and so on.
See also tile() and setTiles().
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QCanvas(3qt)QCanvas(3qt)void QCanvas::setTiles ( QPixmap p, int h, int v, int tilewidth,
int tileheight ) [virtual]
Sets the QCanvas to be composed of h tiles horizontally
and v tiles vertically. Each tile will be an image
tilewidth by tileheight pixels from pixmap p.
The pixmap p contains the tiles arranged left to right,
top to bottom, with tile 0 in the top-left corner, tile 1
to the right of tile 0, and so on.
If the QCanvas is larger than the matrix of tiles, the
entire matrix is repeated as necessary to cover the area.
If it is smaller, tiles to the right and bottom are not
visible.
The width and height of p must be multipless of tilewidth
and tileheight. If they are not, the action of this
function is unspecified.
void QCanvas::setUpdatePeriod ( int ms ) [virtual]
Sets the canvas to call update() every ms milliseconds.
Any previous setting by setAdvancePeriod() or
setUpdatePeriod() is cancelled.
QSize QCanvas::size () const
Returns the size of the canvas, in pixels.
int QCanvas::tile ( int x, int y ) const
Returns the tile at (x, y). Initially, all tiles are 0.
Warning: The parameters must be within range.
See also setTile().
int QCanvas::tileHeight () const
Returns the height of each tile.
int QCanvas::tileWidth () const
Returns the width of each tile.
int QCanvas::tilesHorizontally () const
Returns the number of tiles horizontally.
int QCanvas::tilesVertically () const
Returns the number of tiles vertically.
void QCanvas::update () [virtual slot]
Refreshes all changes to all views of the canvas.
See also advance().
bool QCanvas::validChunk ( const QPoint & p ) const
Returns whether the chunk position p is on the canvas.
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QCanvas(3qt)QCanvas(3qt)bool QCanvas::validChunk ( int x, int y ) const
Returns whether the chunk position (x, y) is on the
canvas.
int QCanvas::width () const
Returns the width of the canvas, in pixels.
void QCanvas::addAnimation ( QCanvasItem * item ) [virtual]
For internal use only.
void QCanvas::addItem ( QCanvasItem * item ) [virtual]
For internal use only.
void QCanvas::addItemToChunk ( QCanvasItem * g, int x, int y )
For internal use only.
void QCanvas::addItemToChunkContaining ( QCanvasItem * g, int x,
int y )
For internal use only.
void QCanvas::addView ( QCanvasView * view ) [virtual]
For internal use only.
void QCanvas::drawArea ( const QRect & inarea, QPainter * p=0,
bool double_buffer=TRUE )
For internal use only.
void QCanvas::removeAnimation ( QCanvasItem * item ) [virtual]
For internal use only.
void QCanvas::removeItem ( QCanvasItem * item ) [virtual]
For internal use only.
void QCanvas::removeItemFromChunk ( QCanvasItem * g, int x, int y
)
For internal use only.
void QCanvas::removeItemFromChunkContaining ( QCanvasItem * g,
int x, int y )
For internal use only.
void QCanvas::removeView ( QCanvasView * view ) [virtual]
For internal use only.
bool QCanvas::sameChunk ( int x1, int y1, int x2, int y2 ) const
For internal use only.
void QCanvas::setChangedChunk ( int x, int y ) [virtual]
For internal use only.
void QCanvas::setChangedChunkContaining ( int x, int y )
[virtual]
For internal use only.
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QCanvas(3qt)QCanvas(3qt)SEE ALSO
http://doc.trolltech.com/qcanvas.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2001 Trolltech AS,
http://www.trolltech.com. See the license file included
in the distribution for a complete license statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page (qcanvas.3qt)
and the Qt version (2.3.1).
Trolltech AS 13 June 2001 10
