Improve drawing of rounded box (STR #2943).

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3-porting@11815 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

1 files changed, 20 insertions, 9 deletions

diff --git a/src/fl_rounded_box.cxx b/src/fl_rounded_box.cxx
index 17cc9de81..3a2f28880 100644
--- a/src/fl_rounded_box.cxx
+++ b/src/fl_rounded_box.cxx
@@ -3,7 +3,7 @@
 //
 // Rounded box drawing routines for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2010 by Bill Spitzak and others.
+// Copyright 1998-2016 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -19,29 +19,40 @@
 #include <FL/Fl.H>
 #include <FL/fl_draw.H>
 
+// Constants for rounded corner drawing algorithm:
+//
+//  RN = number of segments per corner (must match offset array size)
+//  RS = max. corner radius
+//  BW = box shadow width
+
 #define RN	5
 #define RS	15
 #define BW	3
 
 static double offset[RN] = { 0.0, 0.07612, 0.29289, 0.61732, 1.0};
 
+static inline void fl_vertex_r(double x, double y) {
+  fl_vertex(x + 0.5, y + 0.5);
+}
+
 static void rbox(int fill, int x, int y, int w, int h) {
   int i;
-  int rsx ,rsy, rs;
-  rsx = w*2/5; rsy = h*2/5;
-  if (rsx > rsy) rs = rsy; else  rs = rsx;
+  int rs, rsy;
+  rs = w*2/5; rsy = h*2/5;
+  if (rs > rsy) rs = rsy; // use smaller radius
   if (rs > RS) rs = RS;
-  rsx = rs; rsy = rs;
+  if (rs == 5) rs = 4;	// use only even sizes for small corners (STR #2943)
+  if (rs == 7) rs = 8;	// note: 8 is better than 6 (really)
 
   if (fill) fl_begin_polygon(); else fl_begin_loop();
   for (i=0; i<RN; i++)
-    fl_vertex(x + offset[RN-i-1]*rsx, y + offset[i] * rsy);
+    fl_vertex_r(x + offset[RN-i-1]*rs, y + offset[i] * rs);
   for (i=0; i<RN; i++)
-    fl_vertex(x + offset[i]*rsx, y + h-1 - offset[RN-i-1] * rsy);
+    fl_vertex_r(x + offset[i]*rs, y + h-1 - offset[RN-i-1] * rs);
   for (i=0; i<RN; i++)
-    fl_vertex(x + w-1 - offset[RN-i-1]*rsx, y + h-1 - offset[i] * rsy);
+    fl_vertex_r(x + w-1 - offset[RN-i-1]*rs, y + h-1 - offset[i] * rs);
   for (i=0; i<RN; i++)
-    fl_vertex(x + w-1 - offset[i]*rsx, y + offset[RN-i-1] * rsy);
+    fl_vertex_r(x + w-1 - offset[i]*rs, y + offset[RN-i-1] * rs);
   if (fill) fl_end_polygon(); else fl_end_loop();
 }