fixed Inflate() to not move the rectangle (patch 1114622)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@31750 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/rect.tex

@@ -76,14 +76,11 @@ Height member.
 
 \constfunc{wxRect}{Deflate}{\param{wxCoord }{dx}, \param{wxCoord }{dy}}
 
-Decrease the rectangle size by {\it dx} in x direction and {\it dy} in y
-direction. Both (or one of) parameters may be negative to increase the
-rectngle size. This method is the opposite of \helpref{Inflate}{wxrectinflate}.
+Decrease the rectangle size.
 
-The second form uses the same {\it diff} for both {\it dx} and {\it dy}.
-
-The first two versions modify the rectangle in place, the last one returns a
-new rectangle leaving this one unchanged.
+This method is the opposite from \helpref{Inflate}{wxrectinflate}:
+Deflate(a, b) is equivalent to Inflate(-a, -b).
+Please refer to \helpref{Inflate}{wxrectinflate} for full description.
 
 \wxheading{See also}
 
@@ -182,15 +179,39 @@ Gets the y member.
 
 \constfunc{wxRect}{Inflate}{\param{wxCoord }{dx}, \param{wxCoord }{dy}}
 
-Increase the rectangle size by {\it dx} in x direction and {\it dy} in y
-direction. Both (or one of) parameters may be negative to decrease the
-rectangle size.
+Increases the size of the rectangle.
 
 The second form uses the same {\it diff} for both {\it dx} and {\it dy}.
 
 The first two versions modify the rectangle in place, the last one returns a
 new rectangle leaving this one unchanged.
 
+The left border is moved farther left and the right border is moved farther
+right by {\it dx}. The upper border is moved farther up and the bottom border
+is moved farther down by {\it dy}. (Note the the width and height of the
+rectangle thus change by 2*{\it dx} and 2*{\it dy}, respectively.) If one or
+both of {\it dx} and {\it dy} are negative, the opposite happens: the rectangle
+size decreases in the respective direction.
+
+Inflating and deflating behaves ``naturally''. Defined more precisely, that
+means:
+\begin{enumerate}
+    \item ``Real'' inflates (that is, {\it dx} and/or {\it dy} >= 0) are not
+        constrained. Thus inflating a rectangle can cause its upper left corner
+        to move into the negative numbers. (the versions prior to 2.5.4 forced
+        the top left coordinate to not fall below (0, 0), which implied a
+        forced move of the rectangle.)
+
+    \item Deflates are clamped to not reduce the width or height of the
+        rectangle below zero. In such cases, the top-left corner is nonetheless
+        handled properly. For example, a rectangle at (10, 10) with size (20,
+        40) that is inflated by (-15, -15) will become located at (20, 25) at
+        size (0, 10). Finally, observe that the width and height are treated
+        independently. In the above example, the width is reduced by 20,
+        whereas the height is reduced by the full 30 (rather than also stopping
+        at 20, when the width reached zero).
+\end{enumerate}
+
 \wxheading{See also}
 
 \helpref{Deflate}{wxrectdeflate}

src/common/gdicmn.cpp

@@ -163,23 +163,33 @@ wxRect& wxRect::Union(const wxRect& rect)
 
 wxRect& wxRect::Inflate(wxCoord dx, wxCoord dy)
 {
-    x -= dx;
-    y -= dy;
-    width += 2*dx;
-    height += 2*dy;
+     if (-2*dx>width)
+     {
+         // Don't allow deflate to eat more width than we have,
+         // a well-defined rectangle cannot have negative width.
+         x+=width/2;
+         width=0;
+     }
+     else
+     {
+         // The inflate is valid.
+         x-=dx;
+         width+=2*dx;
+     }
 
-    // check that we didn't make the rectangle invalid by accident (you almost
-    // never want to have negative coords and never want negative size)
-    if ( x < 0 )
-        x = 0;
-    if ( y < 0 )
-        y = 0;
-
-    // what else can we do?
-    if ( width < 0 )
-        width = 0;
-    if ( height < 0 )
-        height = 0;
+     if (-2*dy>height)
+     {
+         // Don't allow deflate to eat more height than we have,
+         // a well-defined rectangle cannot have negative height.
+         y+=height/2;
+         height=0;
+     }
+     else
+     {
+         // The inflate is valid.
+         y-=dy;
+         height+=2*dy;
+     }
 
     return *this;
 }

tests/geometry/rect.cpp

@@ -32,10 +32,12 @@ public:
 
 private:
     CPPUNIT_TEST_SUITE( RectTestCase );
+        CPPUNIT_TEST( InflateDeflate );
         CPPUNIT_TEST( Operators );
         CPPUNIT_TEST( Union );
     CPPUNIT_TEST_SUITE_END();
 
+    void InflateDeflate();
     void Operators();
     void Union();
 
@@ -48,6 +50,22 @@ CPPUNIT_TEST_SUITE_REGISTRATION( RectTestCase );
 // also include in it's own registry so that these tests can be run alone
 CPPUNIT_TEST_SUITE_NAMED_REGISTRATION( RectTestCase, "RectTestCase" );
 
+void RectTestCase::InflateDeflate()
+{
+    // This is the rectangle from the example in the documentation of wxRect::Inflate().
+    const wxRect r1(10, 10, 20, 40);
+
+    CPPUNIT_ASSERT(r1.Inflate( 10,  10)==wxRect(  0,   0, 40,  60));
+    CPPUNIT_ASSERT(r1.Inflate( 20,  30)==wxRect(-10, -20, 60, 100));
+    CPPUNIT_ASSERT(r1.Inflate(-10, -10)==wxRect( 20,  20,  0,  20));
+    CPPUNIT_ASSERT(r1.Inflate(-15, -15)==wxRect( 20,  25,  0,  10));
+
+    CPPUNIT_ASSERT(r1.Inflate( 10,  10)==r1.Deflate(-10, -10));
+    CPPUNIT_ASSERT(r1.Inflate( 20,  30)==r1.Deflate(-20, -30));
+    CPPUNIT_ASSERT(r1.Inflate(-10, -10)==r1.Deflate( 10,  10));
+    CPPUNIT_ASSERT(r1.Inflate(-15, -15)==r1.Deflate( 15,  15));
+}
+
 void RectTestCase::Operators()
 {
     // test + operator which works like Union but does not ignore empty rectangles