You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
371 lines
18 KiB
371 lines
18 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/tutorial2.doc:729 -->
|
|
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
|
<title>Canvas Control</title>
|
|
<style type="text/css"><!--
|
|
fn { margin-left: 1cm; text-indent: -1cm; }
|
|
a:link { color: #004faf; text-decoration: none }
|
|
a:visited { color: #672967; text-decoration: none }
|
|
body { background: #ffffff; color: black; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
|
|
<table border="0" cellpadding="0" cellspacing="0" width="100%">
|
|
<tr bgcolor="#E5E5E5">
|
|
<td valign=center>
|
|
<a href="index.html">
|
|
<font color="#004faf">Home</font></a>
|
|
| <a href="classes.html">
|
|
<font color="#004faf">All Classes</font></a>
|
|
| <a href="mainclasses.html">
|
|
<font color="#004faf">Main Classes</font></a>
|
|
| <a href="annotated.html">
|
|
<font color="#004faf">Annotated</font></a>
|
|
| <a href="groups.html">
|
|
<font color="#004faf">Grouped Classes</font></a>
|
|
| <a href="functions.html">
|
|
<font color="#004faf">Functions</font></a>
|
|
</td>
|
|
<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Canvas Control</h1>
|
|
|
|
|
|
<p>
|
|
<p> We draw pie segments (or bar chart bars), and any labels, on a canvas.
|
|
The canvas is presented to the user through a canvas view. The
|
|
drawElements() function is called to redraw the canvas when necessary.
|
|
<p> (Extracts from <tt>chartform_canvas.cpp</tt>.)
|
|
<p> <h2> drawElements()
|
|
</h2>
|
|
<a name="1"></a><p>
|
|
|
|
<pre> void ChartForm::drawElements()
|
|
{
|
|
<a href="qcanvasitemlist.html">TQCanvasItemList</a> list = m_canvas->allItems();
|
|
for ( TQCanvasItemList::iterator it = list.<a href="ntqvaluelist.html#begin">begin</a>(); it != list.<a href="ntqvaluelist.html#end">end</a>(); ++it )
|
|
delete *it;
|
|
</pre>
|
|
<p> The first thing we do in drawElements() is delete all the existing
|
|
canvas items.
|
|
<p> <pre> // 360 * 16 for pies; TQt works with 16ths of degrees
|
|
int scaleFactor = m_chartType == PIE ? 5760 :
|
|
m_chartType == VERTICAL_BAR ? m_canvas->height() :
|
|
m_canvas->width();
|
|
</pre>
|
|
<p> Next we calculate the scale factor which depends on the type of chart
|
|
we're going to draw.
|
|
<p> <pre> double biggest = 0.0;
|
|
int count = 0;
|
|
double total = 0.0;
|
|
static double scales[MAX_ELEMENTS];
|
|
|
|
for ( int i = 0; i < MAX_ELEMENTS; ++i ) {
|
|
if ( m_elements[i].isValid() ) {
|
|
double value = m_elements[i].value();
|
|
count++;
|
|
total += value;
|
|
if ( value > biggest )
|
|
biggest = value;
|
|
scales[i] = m_elements[i].value() * scaleFactor;
|
|
}
|
|
}
|
|
|
|
if ( count ) {
|
|
// 2nd loop because of total and biggest
|
|
for ( int i = 0; i < MAX_ELEMENTS; ++i )
|
|
if ( m_elements[i].isValid() )
|
|
if ( m_chartType == PIE )
|
|
scales[i] = (m_elements[i].value() * scaleFactor) / total;
|
|
else
|
|
scales[i] = (m_elements[i].value() * scaleFactor) / biggest;
|
|
</pre>
|
|
<p> We will need to know how many values there are, the biggest value and
|
|
the total value so that we can create pie segments or bars that are
|
|
correctly scaled. We store the scaled values in the <tt>scales</tt> array.
|
|
<p> <pre> switch ( m_chartType ) {
|
|
case PIE:
|
|
drawPieChart( scales, total, count );
|
|
break;
|
|
case VERTICAL_BAR:
|
|
drawVerticalBarChart( scales, total, count );
|
|
break;
|
|
case HORIZONTAL_BAR:
|
|
drawHorizontalBarChart( scales, total, count );
|
|
break;
|
|
}
|
|
}
|
|
</pre>
|
|
<p> Now that we have the necessary information we call the relevant
|
|
drawing function, passing in the scaled values, the total and the
|
|
count.
|
|
<p> <pre> m_canvas->update();
|
|
</pre>
|
|
<p> Finally we update() the canvas to make the changes visible.
|
|
<p> <h3> drawHorizontalBarChart()
|
|
</h3>
|
|
<a name="1-1"></a><p> We'll review just one of the drawing functions, to see how canvas
|
|
items are created and placed on a canvas since this tutorial is about
|
|
TQt rather than good (or bad) algorithms for drawing charts.
|
|
<p> <pre> void ChartForm::drawHorizontalBarChart(
|
|
const double scales[], double total, int count )
|
|
{
|
|
</pre>
|
|
<p> To draw a horizontal bar chart we need the array of scaled values, the
|
|
total value (so that we can calculate and draw percentages if
|
|
required) and a count of the number of values.
|
|
<p> <pre> double width = m_canvas->width();
|
|
double height = m_canvas->height();
|
|
int proheight = int(height / count);
|
|
int y = 0;
|
|
</pre>
|
|
<p> We retrieve the width and height of the canvas and calculate the
|
|
proportional height (<tt>proheight</tt>). We set the initial <tt>y</tt> position
|
|
to 0.
|
|
<p> <pre> <a href="ntqpen.html">TQPen</a> pen;
|
|
<a name="x2575"></a> pen.<a href="ntqpen.html#setStyle">setStyle</a>( NoPen );
|
|
</pre>
|
|
<p> We create a pen that we will use to draw each bar (rectangle); we set
|
|
it to <tt>NoPen</tt> so that no outlines are drawn.
|
|
<p> <pre> for ( int i = 0; i < MAX_ELEMENTS; ++i ) {
|
|
if ( m_elements[i].isValid() ) {
|
|
int extent = int(scales[i]);
|
|
</pre>
|
|
<p> We iterate over every element in the element vector, skipping invalid
|
|
elements. The extent of each bar (its length) is simply its scaled
|
|
value.
|
|
<p> <pre> <a href="qcanvasrectangle.html">TQCanvasRectangle</a> *rect = new <a href="qcanvasrectangle.html">TQCanvasRectangle</a>(
|
|
0, y, extent, proheight, m_canvas );
|
|
<a name="x2572"></a> rect-><a href="qcanvaspolygonalitem.html#setBrush">setBrush</a>( TQBrush( m_elements[i].valueColor(),
|
|
BrushStyle(m_elements[i].valuePattern()) ) );
|
|
<a name="x2573"></a> rect-><a href="qcanvaspolygonalitem.html#setPen">setPen</a>( pen );
|
|
<a name="x2570"></a> rect-><a href="qcanvasitem.html#setZ">setZ</a>( 0 );
|
|
<a name="x2571"></a> rect-><a href="qcanvasitem.html#show">show</a>();
|
|
</pre>
|
|
<p> We create a new <a href="qcanvasrectangle.html">TQCanvasRectangle</a> for each bar with an x position of 0
|
|
(since this is a horizontal bar chart every bar begins at the left), a
|
|
y value that starts at 0 and grows by the height of each bar as each
|
|
one is drawn, the height of the bar and the canvas that the bar should
|
|
be drawn on. We then set the bar's brush to the color and pattern that
|
|
the user has specified for the element, set the pen to the pen we
|
|
created earlier (i.e. to <tt>NoPen</tt>) and we place the bar at position 0
|
|
in the Z-order. Finally we call show() to draw the bar on the canvas.
|
|
<p> <pre> <a href="ntqstring.html">TQString</a> label = m_elements[i].label();
|
|
<a name="x2576"></a> if ( !label.<a href="ntqstring.html#isEmpty">isEmpty</a>() || m_addValues != NO ) {
|
|
double proX = m_elements[i].proX( HORIZONTAL_BAR );
|
|
double proY = m_elements[i].proY( HORIZONTAL_BAR );
|
|
if ( proX < 0 || proY < 0 ) {
|
|
proX = 0;
|
|
proY = y / height;
|
|
}
|
|
</pre>
|
|
<p> If the user has specified a label for the element or asked for the
|
|
values (or percentages) to be shown, we also draw a canvas text item.
|
|
We created our own CanvasText class (see later) because we want to
|
|
store the corresponding element index (in the element vector) in each
|
|
canvas text item. We extract the proportional x and y values from the
|
|
element. If either is < 0 then they have not been positioned by the
|
|
user so we must calculate positions for them. We set the label's x
|
|
value to 0 (left) and the y value to the top of the bar (so that the
|
|
label's top-left will be at this x, y position).
|
|
<p> <pre> label = valueLabel( label, m_elements[i].value(), total );
|
|
</pre>
|
|
<p> We then call a helper function valueLabel() which returns a string
|
|
containing the label text. (The valueLabel() function adds on the
|
|
value or percentage to the textual label if the user has set the
|
|
appropriate options.)
|
|
<p> <pre> CanvasText *text = new CanvasText( i, label, m_font, m_canvas );
|
|
<a name="x2574"></a> text-><a href="qcanvastext.html#setColor">setColor</a>( m_elements[i].labelColor() );
|
|
<a name="x2568"></a> text-><a href="qcanvasitem.html#setX">setX</a>( proX * width );
|
|
<a name="x2569"></a> text-><a href="qcanvasitem.html#setY">setY</a>( proY * height );
|
|
text-><a href="qcanvasitem.html#setZ">setZ</a>( 1 );
|
|
text-><a href="qcanvasitem.html#show">show</a>();
|
|
m_elements[i].setProX( HORIZONTAL_BAR, proX );
|
|
m_elements[i].setProY( HORIZONTAL_BAR, proY );
|
|
</pre>
|
|
<p> We then create a CanvasText item, passing it the index of this element
|
|
in the element vector, and the label, font and canvas to use. We set
|
|
the text item's text color to the color specified by the user and set
|
|
the item's x and y positions proportional to the canvas's width and
|
|
height. We set the Z-order to 1 so that the text item will always be
|
|
above (in front of) the bar (whose Z-order is 0). We call show() to
|
|
draw the text item on the canvas, and set the element's relative x and
|
|
y positions.
|
|
<p> <pre> }
|
|
y += proheight;
|
|
</pre>
|
|
<p> After drawing a bar and possibly its label, we increment y by the
|
|
proportional height ready to draw the next element.
|
|
<p> <pre> }
|
|
}
|
|
}
|
|
</pre>
|
|
<p> <h2> Subclassing <a href="qcanvastext.html">TQCanvasText</a>
|
|
</h2>
|
|
<a name="2"></a><p> (Extracts from <tt>canvastext.h</tt>.)
|
|
<p>
|
|
|
|
<pre> class CanvasText : public <a href="qcanvastext.html">TQCanvasText</a>
|
|
{
|
|
public:
|
|
enum { CANVAS_TEXT = 1100 };
|
|
|
|
CanvasText( int index, TQCanvas *canvas )
|
|
: <a href="qcanvastext.html">TQCanvasText</a>( canvas ), m_index( index ) {}
|
|
CanvasText( int index, const <a href="ntqstring.html">TQString</a>& text, TQCanvas *canvas )
|
|
: <a href="qcanvastext.html">TQCanvasText</a>( text, canvas ), m_index( index ) {}
|
|
CanvasText( int index, const <a href="ntqstring.html">TQString</a>& text, TQFont font, TQCanvas *canvas )
|
|
: <a href="qcanvastext.html">TQCanvasText</a>( text, font, canvas ), m_index( index ) {}
|
|
|
|
int index() const { return m_index; }
|
|
void setIndex( int index ) { m_index = index; }
|
|
|
|
int rtti() const { return CANVAS_TEXT; }
|
|
|
|
private:
|
|
int m_index;
|
|
};
|
|
</pre>
|
|
<p> Our CanvasText subclass is a very simple specialisation of
|
|
<a href="qcanvastext.html">TQCanvasText</a>. All we've done is added a single private member <tt>m_index</tt> which holds the element vector index of the element associated
|
|
with this text item, and provided a getter and setter for this value.
|
|
<p> <h2> Subclassing <a href="qcanvasview.html">TQCanvasView</a>
|
|
</h2>
|
|
<a name="3"></a><p> (Extracts from <tt>canvasview.h</tt>.)
|
|
<p>
|
|
|
|
<pre> class CanvasView : public <a href="qcanvasview.html">TQCanvasView</a>
|
|
{
|
|
<a href="metaobjects.html#Q_OBJECT">Q_OBJECT</a>
|
|
public:
|
|
CanvasView( <a href="ntqcanvas.html">TQCanvas</a> *canvas, ElementVector *elements,
|
|
<a href="ntqwidget.html">TQWidget</a>* parent = 0, const char* name = "canvas view",
|
|
WFlags f = 0 )
|
|
: <a href="qcanvasview.html">TQCanvasView</a>( canvas, parent, name, f ), m_movingItem(0),
|
|
m_elements( elements ) {}
|
|
|
|
protected:
|
|
void viewportResizeEvent( <a href="qresizeevent.html">TQResizeEvent</a> *e );
|
|
void contentsMousePressEvent( <a href="qmouseevent.html">TQMouseEvent</a> *e );
|
|
void contentsMouseMoveEvent( <a href="qmouseevent.html">TQMouseEvent</a> *e );
|
|
void contentsContextMenuEvent( <a href="qcontextmenuevent.html">TQContextMenuEvent</a> *e );
|
|
|
|
private:
|
|
<a href="qcanvasitem.html">TQCanvasItem</a> *m_movingItem;
|
|
<a href="ntqpoint.html">TQPoint</a> m_pos;
|
|
ElementVector *m_elements;
|
|
};
|
|
</pre>
|
|
<p> We need to subclass <a href="qcanvasview.html">TQCanvasView</a> so that we can handle:
|
|
<ol type=1>
|
|
<li> Context menu requests.
|
|
<li> Form resizing.
|
|
<li> Users dragging labels to arbitrary positions.
|
|
</ol>
|
|
<p> To support these we store a pointer to the canvas item that is being
|
|
moved and its last position. We also store a pointer to the element
|
|
vector.
|
|
<p> <h3> Supporting Context Menus
|
|
</h3>
|
|
<a name="3-1"></a><p> (Extracts from <tt>canvasview.cpp</tt>.)
|
|
<p>
|
|
|
|
<pre> <a name="x2584"></a>void CanvasView::<a href="ntqscrollview.html#contentsContextMenuEvent">contentsContextMenuEvent</a>( <a href="qcontextmenuevent.html">TQContextMenuEvent</a> * )
|
|
{
|
|
<a name="x2579"></a> ((ChartForm*)<a href="ntqobject.html#parent">parent</a>())->optionsMenu->exec( TQCursor::<a href="ntqcursor.html#pos">pos</a>() );
|
|
}
|
|
</pre>
|
|
<p> When the user invokes a context menu (e.g. by right-clicking on most
|
|
platforms) we cast the canvas view's parent (which is the chart form)
|
|
to the right type and then exec()ute the options menu at the cursor
|
|
position.
|
|
<p> <h3> Handling Resizing
|
|
</h3>
|
|
<a name="3-2"></a><p> <pre> <a name="x2587"></a>void CanvasView::<a href="ntqscrollview.html#viewportResizeEvent">viewportResizeEvent</a>( <a href="qresizeevent.html">TQResizeEvent</a> *e )
|
|
{
|
|
<a name="x2583"></a> <a href="qcanvasview.html#canvas">canvas</a>()->resize( e-><a href="qresizeevent.html#size">size</a>().width(), e-><a href="qresizeevent.html#size">size</a>().height() );
|
|
((ChartForm*)<a href="ntqobject.html#parent">parent</a>())->drawElements();
|
|
}
|
|
</pre>
|
|
<p> To resize we simply resize the canvas that the canvas view is
|
|
presenting to the width and height of the form's client area, then
|
|
call drawElements() to redraw the chart. Because drawElements() draws
|
|
everything relative to the canvas's width and height the chart is
|
|
drawn correctly.
|
|
<p> <h3> Dragging Labels into Position
|
|
</h3>
|
|
<a name="3-3"></a><p> When the user wants to drag a label into position they click it, then
|
|
drag and release at the new position.
|
|
<p> <pre> <a name="x2586"></a>void CanvasView::<a href="ntqscrollview.html#contentsMousePressEvent">contentsMousePressEvent</a>( <a href="qmouseevent.html">TQMouseEvent</a> *e )
|
|
{
|
|
<a name="x2580"></a> <a href="qcanvasitemlist.html">TQCanvasItemList</a> list = <a href="qcanvasview.html#canvas">canvas</a>()->collisions( e-><a href="qmouseevent.html#pos">pos</a>() );
|
|
<a name="x2589"></a><a name="x2588"></a> for ( TQCanvasItemList::iterator it = list.<a href="ntqvaluelist.html#begin">begin</a>(); it != list.<a href="ntqvaluelist.html#end">end</a>(); ++it )
|
|
if ( (*it)->rtti() == CanvasText::CANVAS_TEXT ) {
|
|
m_movingItem = *it;
|
|
m_pos = e-><a href="qmouseevent.html#pos">pos</a>();
|
|
return;
|
|
}
|
|
m_movingItem = 0;
|
|
}
|
|
</pre>
|
|
<p> When the user clicks the mouse we create a list of canvas items that
|
|
the mouse click "collided" with (if any). We then iterate over this
|
|
list and if we find a <tt>CanvasText</tt> item we set it as the moving item
|
|
and record its position. Otherwise we set there to be no moving item.
|
|
<p> <pre> <a name="x2585"></a>void CanvasView::<a href="ntqscrollview.html#contentsMouseMoveEvent">contentsMouseMoveEvent</a>( <a href="qmouseevent.html">TQMouseEvent</a> *e )
|
|
{
|
|
if ( m_movingItem ) {
|
|
<a href="ntqpoint.html">TQPoint</a> offset = e-><a href="qmouseevent.html#pos">pos</a>() - m_pos;
|
|
<a name="x2582"></a><a name="x2581"></a> m_movingItem->moveBy( offset.<a href="ntqpoint.html#x">x</a>(), offset.<a href="ntqpoint.html#y">y</a>() );
|
|
m_pos = e-><a href="qmouseevent.html#pos">pos</a>();
|
|
ChartForm *form = (ChartForm*)<a href="ntqobject.html#parent">parent</a>();
|
|
form->setChanged( TRUE );
|
|
int chartType = form->chartType();
|
|
CanvasText *item = (CanvasText*)m_movingItem;
|
|
int i = item->index();
|
|
|
|
(*m_elements)[i].setProX( chartType, item->x() / canvas()->width() );
|
|
(*m_elements)[i].setProY( chartType, item->y() / canvas()->height() );
|
|
|
|
<a href="qcanvasview.html#canvas">canvas</a>()->update();
|
|
}
|
|
}
|
|
</pre>
|
|
<p> As the user drags the mouse, move events are generated. If there is a
|
|
moving item we calculate the offset from the last mouse position and
|
|
move the item by this offset amount. We record the new position as the
|
|
last position. Because the chart has now changed we call setChanged()
|
|
so that the user will be prompted to save if they attempt to exit or
|
|
to load an existing chart or to create a new chart. We also update the
|
|
element's proportional x and y positions for the current chart type to
|
|
the current x and y positions proportional to the width and height
|
|
respectively. We know which element to update because when we create
|
|
each canvas text item we pass it the index position of the element it
|
|
corresponds to. We subclassed <a href="qcanvastext.html">TQCanvasText</a> so that we could set and get
|
|
this index value. Finally we call update() to make the canvas redraw.
|
|
<p> <center><table cellpadding="4" cellspacing="2" border="0">
|
|
<tr bgcolor="#f0f0f0">
|
|
<td valign="top">A <a href="ntqcanvas.html">TQCanvas</a> has no visual representation. To see the contents of a
|
|
canvas you must create a <a href="qcanvasview.html">TQCanvasView</a> to present the canvas. Items only
|
|
appear in the canvas view if they have been show()n, and then, only if
|
|
<a href="ntqcanvas.html#update">TQCanvas::update</a>() has been called. By default a TQCanvas's background
|
|
color is white, and by default shapes drawn on the canvas, e.g.
|
|
<a href="qcanvasrectangle.html">TQCanvasRectangle</a>, <a href="qcanvasellipse.html">TQCanvasEllipse</a>, etc., have their fill color set to
|
|
white, so setting a non-white brush color is highly recommended!
|
|
</table></center>
|
|
<p> <p align="right">
|
|
<a href="tutorial2-05.html">« Presenting the GUI</a> |
|
|
<a href="tutorial2.html">Contents</a> |
|
|
<a href="tutorial2-07.html">File Handling »</a>
|
|
</p>
|
|
<p>
|
|
<!-- eof -->
|
|
<p><address><hr><div align=center>
|
|
<table width=100% cellspacing=0 border=0><tr>
|
|
<td>Copyright © 2007
|
|
<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
|
|
<td align=right><div align=right>TQt 3.3.8</div>
|
|
</table></div></address></body>
|
|
</html>
|