Advanced MFC Programming

Chapter 11. Sample: Simple Paint
……
)
{
)
if
(
)
{
m_trackerSel.m_rect.IsRectEmpty() != TRUE &&
m_trackerSel.SetCursor(this, nHitTest) == TRUE
MouseWithinBitmap() == TRUE &&
HTVSCROLL != nHitTest && HTHSCROLL != nHitTest
::SetCursor(AfxGetApp()->LoadStandardCursor(IDC_CROSS));
return TRUE;
}
}
else return TRUE;
Here we first check if the cursor can be set automatically. If CRectTracker::SetCursor(…) returns
TRUE, we can exit and return a TRUE value (If this function returns TRUE, it means currently the mouse
cursor is within the tracker region, and the cursor is customized by the tracker). If not, we check if the
mouse is over the bitmap image, if so, the cursor’s shape is set to IDC_CROSS and the function exits (We
need to return TRUE every time the cursor has been customized). If all these fail, we need to call function
CWnd::SetCursor(…) to set the cursor to the default shape.
If Mouse Clicking Doesn’t Hit the Tracker
We must implement a way of letting the user create tracker interactively. Like line drawing
implementations, we need to handle WM_LBUTTONDOWN, WM_RBUTTONDOWN and WM_MOUSEMOVE messages in
order to let the user create tracker by mouse clicking. This procedure is similar to rectangle drawing: when
left button is pressed down, we need to record the current mouse position as the starting point; as the mouse
is dragged around, we draw a series of temporary rectangles; when the left button is released, we use the
current mouse position as the ending point and use it along with the starting point to draw the tracker.
For the tracker, there are two possibilities when the mouse button is pressed down. If currently there is
an existing tracker and the mouse hits the tracker, we should let the tracker be moved or resized instead of
creating a new tracker. If there is no tracker currently implemented or the mouse did not hit the existing
tracker, we should start creating a new tracker.
This situation can be judged by calling function CTracker::HitTest(…), whose input parameter
should be set to the current position of mouse cursor that is measured in the client window’s coordinate
system. If the function returns CRectTracker::hitNothing, either there is no existing tracker or the mouse
didn’t hit any portion of the tracker. In the sample, this situation is handled as follows:
……
……
case TOOL_RECTSEL:
{
int nHitTest;
nHitTest=m_trackerSel.HitTest(point);
if(nHitTest == CRectTracker::hitNothing)
{
m_trackerSel.m_rect.left=
m_trackerSel.m_rect.right=
point.x+GetScrollPosition().x;
m_trackerSel.m_rect.top=
m_trackerSel.m_rect.bottom=
point.y+GetScrollPosition().y;
}
We record the starting position in the upper-left point of the tracker rectangle. As the mouse moves,
the rectangle’s bottom-right point is updated with the current mouse position, and temporary rectangles are
drawn and erased before the tracker is finally fixed.
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