Make results of wxDC::DrawEllipticArc() consistent across all platforms.

And also consistent with wxGraphicsContext method with the same name.

Document the rules determining what is drawn.

Closes #4437.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78125 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -58,6 +58,7 @@ All (GUI):
 
 - Allow requesting modern (3.x+) OpenGL version in wxGLCanvas (Fabio Arnold).
 - Allow customizing window shown by wxBusyInfo.
+- Make results of wxDC::DrawEllipticArc() consistent across all platforms.
 - XRC handler for wxAuiToolBar added (Kinaou Hervé, David Hart).
 - Add wxFD_NO_FOLLOW style for wxFileDialog (Luca Bacci).
 - Add support for embedding bitmaps in generated SVG in wxSVGFileDC (iwbnwif).

interface/wx/dc.h

@@ -356,12 +356,14 @@ public:
         @a width and @a height specify the width and height of the rectangle
         that contains the ellipse.
 
-        @a start and @a end specify the start and end of the arc relative to
+        @a start and @a end specify the end points of the arc relative to
         the three-o'clock position from the center of the rectangle. Angles are
         specified in degrees with 0 degree angle corresponding to the positive
-        horizontal axis (3 o'clock) direction. Positive values mean
-        counter-clockwise motion. If @a start is equal to @e end, a complete
-        ellipse will be drawn.
+        horizontal axis (3 o'clock) direction.
+
+        Independently of whether @a start is greater than or less than @a end,
+        the arc is drawn in the counter-clockwise direction. Also, if @a start
+        is equal to @e end, a complete ellipse is drawn.
 
         Notice that unlike DrawArc(), this function does not draw the lines to
         the arc ends, even when using non-transparent brush.

src/common/dcgraph.cpp

@@ -646,22 +646,27 @@ void wxGCDCImpl::DoDrawEllipticArc( wxCoord x, wxCoord y, wxCoord w, wxCoord h,
     m_graphicContext->Scale(factor, 1.0);
     wxGraphicsPath path = m_graphicContext->CreatePath();
 
+    // If end angle equals start angle we want draw a full ellipse.
+    if (ea == sa)
+    {
+        ea += 360.0;
+    }
     // since these angles (ea,sa) are measured counter-clockwise, we invert them to
     // get clockwise angles
     if ( m_brush.GetStyle() != wxBRUSHSTYLE_TRANSPARENT )
     {
         path.MoveToPoint( 0, 0 );
-        path.AddArc( 0, 0, h/2.0, wxDegToRad(-sa), wxDegToRad(-ea), sa > ea );
+        path.AddArc( 0, 0, h/2.0, wxDegToRad(-sa), wxDegToRad(-ea), false );
         path.AddLineToPoint( 0, 0 );
         m_graphicContext->FillPath( path );
 
         path = m_graphicContext->CreatePath();
-        path.AddArc( 0, 0, h/2.0, wxDegToRad(-sa), wxDegToRad(-ea), sa > ea );
+        path.AddArc( 0, 0, h/2.0, wxDegToRad(-sa), wxDegToRad(-ea), false );
         m_graphicContext->StrokePath( path );
     }
     else
     {
-        path.AddArc( 0, 0, h/2.0, wxDegToRad(-sa), wxDegToRad(-ea), sa > ea );
+        path.AddArc( 0, 0, h/2.0, wxDegToRad(-sa), wxDegToRad(-ea), false );
         m_graphicContext->DrawPath( path );
     }
 

src/gtk/dcclient.cpp

@@ -663,6 +663,16 @@ void wxWindowDCImpl::DoDrawEllipticArc( wxCoord x, wxCoord y, wxCoord width, wxC
     {
         wxCoord start = wxCoord(sa * 64.0);
         wxCoord end = wxCoord((ea-sa) * 64.0);
+        // We want to draw always in the counter-clokwise direction.
+        if (end < 0)
+        {
+            end = end % (360*64) + 360*64;
+        }
+        // If end angle equals start engle we want to draw a full ellipse.
+        if (end == 0)
+        {
+            end = 360*64;
+        }
 
         if ( m_brush.IsNonTransparent() )
         {

src/msw/dc.cpp

@@ -1290,17 +1290,6 @@ void wxMSWDCImpl::DoDrawEllipticArc(wxCoord x,wxCoord y,wxCoord w,wxCoord h,doub
     rx2 += (int)(100.0 * abs(w) * cos(ea));
     ry2 -= (int)(100.0 * abs(h) * m_signY * sin(ea));
 
-    // Swap start and end positions if the end angle is less than the start angle.
-    if (ea < sa) {
-        int temp;
-        temp = rx2;
-        rx2 = rx1;
-        rx1 = temp;
-        temp = ry2;
-        ry2 = ry1;
-        ry1 = temp;
-    }
-
     // draw pie with NULL_PEN first and then outline otherwise a line is
     // drawn from the start and end points to the centre
     HPEN hpenOld = (HPEN) ::SelectObject(GetHdc(), (HPEN) ::GetStockObject(NULL_PEN));