ch12.htm

24小时学会vc++

<UL>
	<LI><TT>Ellipse</TT>: Used to draw an ellipse. This function is also used to draw
	circles, because a circle is just a special type of ellipse.<BR>
	<BR>
	
	<LI><TT>Arc</TT>: Used to draw a portion of an ellipse.<BR>
	<BR>
	
	<LI><TT>LineTo</TT> and <TT>MoveTo</TT>: Used to draw lines. Together they are often
	used to draw highlighting, squares, rectangles, and other types of figures.
</UL>

<P>As an example using pens, you can modify the DCTest program you created in Hour
11. The changes use three pens to draw three figures in the view window in a variety
of styles and colors. Modifying the existing project also gives you a chance to see
how different mapping modes affect the figures drawn using pens. Although some of
the listings might look long, most of them require only a few changes in the source
code that is already present.
<H3><FONT COLOR="#000077"><B>Modifying the Mapping Mode Dialog Box</B></FONT></H3>
<P>As the first step in the sample program, modify the Mapping Mode dialog box and
the <TT>CMapModeDlg</TT> class to support extra options used when drawing with pens.
The new version of the <TT>IDD_MAP_MODE</TT> dialog box is shown in Figure 12.2.</P>
<P><A NAME="02"></A><A HREF="02.htm"><B>Figure 12.2.</B> </A><I><BR>
The new version of the Mapping Mode dialog box.</I></P>
<P>Use the values from Table 12.1 for the new controls you add to the Mapping Mode
dialog box, using ClassWizard to add member variables to the <TT>CMapModeDlg</TT>
class. All existing controls should remain as they are.
<H4><FONT COLOR="#000077">Table 12.1. Values for new edit controls you add to the
Mapping Mode dialog box.</FONT></H4>
<P>
<TABLE BORDER="1">
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Edit Control</B></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Resource ID</B></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Variable Name</B></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><B>Type</B></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP">Pen Width</TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDC_WIDTH</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>m_nPenWidth</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>int</TT></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP">Ellipse Width</TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDC_CXELLIPSE</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>m_cxEllipse</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>int</TT></TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP">Ellipse Height</TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDC_CYELLIPSE</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>m_cyEllipse</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>int</TT></TD>
	</TR>
</TABLE>

<H3><FONT COLOR="#000077"><B>Modifying the <TT>CDCTestView</TT> Class</B></FONT></H3>
<P>You must modify the <TT>CDCTestView</TT> class slightly to add three new member
variables that store the pen height and the ellipse variables you just added to the
dialog box class. Add three new member variables to the attributes section of the
<TT>CDCTestView</TT> class declaration, as shown in Listing 12.2.
<H4><FONT COLOR="#000077">TYPE: Listing 12.2. New member variables added to the CDCTestView
class.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>// Attributes</TT>
<TT>private:</TT>
<TT>    // Variables added for Hour 11</TT>
<TT>    CMap&lt; int, int, CString, CString &gt; m_map;</TT>
<TT>    int     m_nMapMode;</TT>
<TT>    // Variables added for Hour 12 - pens</TT>
<TT>    int     m_cxEllipse;</TT>
<TT>    int     m_cyEllipse;</TT>
<TT>    int     m_nPenWidth;</TT>
</FONT></PRE>
<P>Do not modify the declarations for existing member variables.
<H3><FONT COLOR="#000077"><B>Modifying the <TT>CDCTestView</TT> Member Functions</B></FONT></H3>
<P>You must modify three <TT>CDCTestView</TT> member functions:

<UL>
	<LI>The <TT>CDCTestView</TT> constructor
	<LI>The <TT>CDCTestView::OnViewMapMode</TT> menu handler
	<LI>The <TT>CDCTestView::OnDraw</TT> member function
</UL>

<P>Each of these views is modified in the following sections. None of these member
functions are new; all are used in the current DCTest project.</P>
<P>Add three new lines to the <TT>CDCTestView</TT> constructor to initialize the
new variables added to the <TT>CDCTestView</TT> class. Listing 12.3 is the new version
of the <TT>CDCTestView</TT> constructor. Most of the function should already be entered;
you must add only the last three lines before the closing parenthesis.
<H4><FONT COLOR="#000077">TYPE: Listing 12.3. The new version of the CDCTestView
constructor.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>CDCTestView::CDCTestView()</TT>
<TT>{</TT>
<TT>    m_nMapMode = MM_TEXT;</TT>
<TT>    m_map.SetAt( MM_ANISOTROPIC, &quot;MM_ANISOTROPIC&quot; );</TT>
<TT>    m_map.SetAt( MM_HIENGLISH, &quot;MM_HIENGLISH&quot; );</TT>
<TT>    m_map.SetAt( MM_HIMETRIC, &quot;MM_HIMETRIC&quot; );</TT>
<TT>    m_map.SetAt( MM_ISOTROPIC, &quot;MM_ISOTROPIC&quot; );</TT>
<TT>    m_map.SetAt( MM_LOENGLISH, &quot;MM_LOENGLISH&quot; );</TT>
<TT>    m_map.SetAt( MM_LOMETRIC, &quot;MM_LOMETRIC&quot; );</TT>
<TT>    m_map.SetAt( MM_TEXT, &quot;MM_TEXT&quot; );</TT>
<TT>    m_map.SetAt( MM_TWIPS, &quot;MM_TWIPS&quot; );</TT>
<TT>    m_nPenWidth = 1;</TT>
<TT>    m_cxEllipse = 100;</TT>
<TT>    m_cyEllipse = 200;</TT>
<TT>}</TT>
</FONT></PRE>
<P>Modify the <TT>CDCTestView::OnViewMapMode</TT> function to handle the changes
in the Mapping Mode dialog box. Listing 12.4 provides the source code for the new
version of <TT>OnViewMapMode</TT>. There are a total of six new source code lines,
each marked with a comment. You should need to add only these six lines; the rest
of the function should have been created already.
<H4><FONT COLOR="#000077">Listing 12.4. The new version of the CDCTestView::OnViewMapMode
function.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>void CDCTestView::OnViewMapMode()</TT>
<TT>{</TT>
<TT>    CMapModeDlg dlg;</TT>
<TT>    // The next three lines are added for Hour 12 - pens</TT>
<TT>    dlg.m_nPenWidth = m_nPenWidth;  // 1</TT>
<TT>    dlg.m_cxEllipse = m_cxEllipse;  // 2</TT>
<TT>    dlg.m_cyEllipse = m_cyEllipse;  // 3</TT>
<TT>    if( dlg.DoModal() == IDOK )</TT>
<TT>    {</TT>
<TT>        // The next three lines are added for Hour 12 - pens</TT>
<TT>        m_nPenWidth = dlg.m_nPenWidth;  // 4</TT>
<TT>        m_cxEllipse = dlg.m_cxEllipse;  // 5</TT>
<TT>        m_cyEllipse = dlg.m_cyEllipse;  // 6</TT>
<TT>        POSITION    pos;</TT>
<TT>        pos = m_map.GetStartPosition();</TT>
<TT>        while( pos != NULL )</TT>
<TT>        {</TT>
<TT>            CString szMapMode;</TT>
<TT>            int     nMapMode;</TT>
<TT>            m_map.GetNextAssoc( pos, nMapMode, szMapMode  );</TT>
<TT>            if( szMapMode == dlg.m_szCombo )</TT>
<TT>            {</TT>
<TT>                m_nMapMode = nMapMode;</TT>
<TT>                break;</TT>
<TT>            }</TT>
<TT>        }</TT>
<TT>        InvalidateRect( NULL );</TT>
<TT>    }</TT>
<TT>}</TT>
</FONT></PRE>
<P>Last but not least, you must create a new version of the <TT>OnDraw</TT> function.
Most of this version of <TT>OnDraw</TT> is new because you are now drawing with pens
instead of listing device attributes. Use the source code provided in Listing 12.5
for the new version of <TT>CDCTestView::OnDraw</TT>.
<H4><FONT COLOR="#000077">Listing 12.5. The new version of CDCTestView::OnDraw.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>void CDCTestView::OnDraw(CDC* pDC)</TT>
<TT>{</TT>
<TT>    pDC-&gt;SetMapMode( m_nMapMode );</TT>
<TT>    // Draw an ellipse based on the current map-mode and values</TT>
<TT>    // supplied by the user.</TT>
<TT>    CRect   rcClient;</TT>
<TT>    GetClientRect( rcClient );</TT>
<TT>    pDC-&gt;DPtoLP( rcClient );    // Covert device units to logical</TT>
<TT>    CPoint  ptCenter( rcClient.Width()/2, rcClient.Height()/2 );</TT>
<TT>    CRect   rcEllipse( ptCenter.x - ( m_cxEllipse/2 ),</TT>
<TT>                       ptCenter.y - ( m_cyEllipse/2 ),</TT>
<TT>                       ptCenter.x + ( m_cxEllipse/2 ),</TT>
<TT>                       ptCenter.y + ( m_cyEllipse/2 ) );</TT>
<TT>    CPen    penRed( PS_SOLID, m_nPenWidth, RGB(255,0,0) );</TT>
<TT>    CPen*   pOldPen = pDC-&gt;SelectObject( &amp;penRed );</TT>
<TT>    pDC-&gt;Ellipse( rcEllipse );</TT>
<TT>    // Draw a black box around the ellipse, using one of the stock</TT>
<TT>    // pens.</TT>
<TT>    pDC-&gt;SelectStockObject( BLACK_PEN );</TT>
<TT>    pDC-&gt;MoveTo( rcEllipse.TopLeft() );</TT>
<TT>    pDC-&gt;LineTo( rcEllipse.right, rcEllipse.top );</TT>
<TT>    pDC-&gt;LineTo( rcEllipse.BottomRight() );</TT>
<TT>    pDC-&gt;LineTo( rcEllipse.left, rcEllipse.bottom );</TT>
<TT>    pDC-&gt;LineTo( rcEllipse.left, rcEllipse.top );</TT>
<TT>    // Draw an arc using the client area as a bounding rectangle.</TT>
<TT>    // Clip the arc so that only the lower-left half is displayed.</TT>
<TT>    CPen    penDottedAndGreen( PS_DOT, 1, RGB(0,255,0) );</TT>
<TT>    pDC-&gt;SelectObject( &amp;penDottedAndGreen );</TT>
<TT>    pDC-&gt;Arc(rcClient, rcClient.TopLeft(),rcClient.BottomRight());</TT>
<TT>    pDC-&gt;SelectObject( &amp;pOldPen );</TT>
<TT>}</TT>
</FONT></PRE>
<P>Compile and run the DCTest project, and experiment by changing the values in the
Mapping Mode dialog box. Figure 12.3 shows the DCTest project running with the mapping
mode set to <TT>MM_TEXT</TT>.</P>
<P><A NAME="03"></A><A HREF="03.htm"><B>Figure 12.3.</B> </A><I><BR>
The DCTest example after adding pen GDI objects.</I>
<H2><FONT COLOR="#000077"><B>What Are Brushes?</B></FONT></H2>
<P>A brush is a GDI object used to fill a control, window, or other area when programming
for Windows. A brush is much like a pen; both are selected the same way, some of
the attributes are similar, and you can use a series of stock objects without much
overhead. However, you use a brush to fill an area rather than draw a line or a figure.
A common use for brushes is to color windows, controls, or dialog boxes.</P>
<P>Every brush has several attributes:

<UL>
	<LI><I>Color:</I> Specifies the brush color. You use a <TT>COLORREF</TT> value, just
	as when you specify a pen color.<BR>
	<BR>
	
	<LI><I>Pattern:</I> Defines the pattern used by the brush.<BR>
	<BR>
	
	<LI><I>Hatching Style:</I> Specifies a hatch pattern.
</UL>

<P>By choosing different values for attributes given to a brush, you can achieve
a wide variety of effects.
<H3><FONT COLOR="#000077"><B>MFC Support for Brushes</B></FONT></H3>
<P>In a program you write with Visual C++, you normally create and use <TT>CBrush</TT>
objects the way you create and use <TT>CPen</TT> objects. Every brush has a set of
attributes that define how it appears and behaves. Just as with pens, Windows has
several stock brushes that are available by calling the <TT>SelectStockObject</TT>
function.</P>
<P>Your Windows program can create four basic types of brushes:

<UL>
	<LI>Solid brushes: Similar to solid pens, except they are used to fill areas instead
	of drawing lines. You normally give these brushes a color when you use a <TT>COLORREF</TT>
	to create them.<BR>
	<BR>
	
	<LI>Stock brushes: Predefined brushes stored and maintained by Windows.<BR>
	<BR>
	
	<LI>Hatch brushes: Fill an area with a predefined hatch pattern, as shown in Figure
	12.4. These brushes can also be colored when they are created.<BR>
	<BR>
	
	<LI>Pattern brushes: Fill an area with a pattern supplied in an 8x8 bitmap, as shown
	in Figure 12.4.
</UL>

<P><A NAME="04"></A><A HREF="04.htm"><B>Figure 12.4.</B> </A><I><BR>
Examples of styles available for brushes.</I></P>
<P>You create each of these brush types using a different function call. For example,
a solid brush is created using <TT>CreateSolidBrush</TT>, whereas a hatched brush
is created using <TT>CreateHatchBrush</TT>. When using the <TT>CBrush</TT> class,
it's also possible to call a specialized <TT>CBrush</TT> constructor to construct
the <TT>CBrush</TT> object in the desired style. You will use the <TT>CBrush</TT>
class later in this hour.</P>
<P>You can create solid and hatch brushes with a color attribute that specifies the
color used when the brush fills an area. In the case of a hatched brush, the color
specifies the color of the hatching lines.
<H3><FONT COLOR="#000077"><B>Hatch Styles for Brushes</B></FONT></H3>
<P>Six hatch styles are available for hatch brushes. You create a hatch style by
passing one of the following styles as a parameter when you create the brush:

<UL>