Advanced MFC Programming

Chapter 11. Sample: Simple Paint
customized (The cursor is over tracker’s region). In this case we can exit and return a TRUE value.
Otherwise we must call function CWnd::OnSetCursor(…) to let the cursor’s shape be set to the default one.
New Tool
In the new sample application, a new tool “Rectangular Selection” is implemented in tool bar
IDR_DRAWTOOLBAR (Figure 11-5). If it is selected as the current tool, the user can drag the mouse to create a
tracker over the image, resize or move it to change the selection. The cursor will be automatically changed
if the mouse cursor is within the tracker’s region.
“Rectangular
Selection” button on
the tool bar
Figure 11-5. Tool “Rectangular Selection”
First, a new command ID_BUTTON_RECSEL is added to IDR_DRAWTOOL tool bar. Each time a new tool
command is added to the tool bar, we must make sure that the IDs of all the commands contained in the
tool bar are consecutive. Otherwise the macros ON_COMMAND_RANGE and ON_UPDATE_COMMAND_UI_RANGE will
not work correctly. In the sample, two macros TOOL_HEAD_ID and TOOL_TAIL_ID are defined, and they
represent the first and last IDs of the commands contained in the drawing tool bar. We use the above two
macros to do the message mapping. By doing this, if we add a new tool next time, all we need to do is
redefining the macros.
In class CGDIView, a CRectTracker type variable m_trackerSel is declared to implement the tracker.
The tracker’s styles are initialized in the constructor as follows:
……
……
m_trackerSel.m_nStyle=
(
CRectTracker::dottedLine | CRectTracker::resizeOutside
);
The tracker’s border is formed by dotted line and the resize buttons are located outside the rectangle.
The tracker is drawn in function CGDIView::OnDraw(…) if the tracker rectangle is not empty:
……
……
CPoint ptScroll;
ptScroll=GetScrollPosition();
m_trackerSel.m_rect.OffsetRect(-ptScroll);
m_trackerSel.Draw(pDC);
m_trackerSel.m_rect.OffsetRect(ptScroll);
As we will see, the tracker’s size and position will be recorded in the zoomed bitmap image’s
coordinate system. This is for the convenience of coordinate conversion. Since the DC will draw the tracker
in client window’s coordinate system, we must add some offset to the tracker rectangle before it is drawn.
Also we need to resume rectangle’s original state after the drawing is completed.
Function CGDIView::OnSetCursor(…) is modified as follows so that the cursor will be automatically
changed if it is over the tracker region:
……
if(m_bmpDraw.GetSafeHandle() != NULL)
{
if
(
!(
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