Refactor code to make rounded rectangles accessible (#553)

This adds fl_rounded_rect and fl_rounded_rectf so the
user can draw rounded rectangles. This uses existing and
optimised code that is rearranged.

FL/Fl_Graphics_Driver.H

@@ -264,6 +264,9 @@ public:
   virtual void rect(int x, int y, int w, int h);
   virtual void focus_rect(int x, int y, int w, int h);
   virtual void rectf(int x, int y, int w, int h);
+  virtual void _rbox(int fill, int x, int y, int w, int h, int r);
+  virtual void rounded_rect(int x, int y, int w, int h, int r);
+  virtual void rounded_rectf(int x, int y, int w, int h, int r);
   // the default implementation is most likely enough
   virtual void colored_rectf(int x, int y, int w, int h, uchar r, uchar g, uchar b);
   virtual void line(int x, int y, int x1, int y1);

FL/fl_draw.H

@@ -290,6 +290,15 @@ inline void fl_rect(int x, int y, int w, int h) {
   fl_graphics_driver->rect(x, y, w, h);
 }
 
+/**
+ Draw a 1-pixel rounded border \e inside the given bounding box.
+ The radius code is optimized for speed and works best for values between
+ 5 and 15 units.
+ */
+inline void fl_rounded_rect(int x, int y, int w, int h, int r) {
+  fl_graphics_driver->rounded_rect(x, y, w, h, r);
+}
+
 /**
   Draw a 1-pixel border \e inside the given bounding box.
   This is the same as fl_rect(int x, int y, int w, int h) but with
@@ -320,6 +329,14 @@ inline void fl_rectf(int x, int y, int w, int h) {
   fl_graphics_driver->rectf(x, y, w, h);
 }
 
+/** Color with current color a rounded rectangle that exactly fills the given bounding box.
+ The radius code is optimized for speed and works best for values between
+ 5 and 15 units.
+*/
+inline void fl_rounded_rectf(int x, int y, int w, int h, int r) {
+  fl_graphics_driver->rounded_rectf(x, y, w, h, r);
+}
+
 /** Color with passed color a rectangle that exactly fills the given bounding box. */
 inline void fl_rectf(int x, int y, int w, int h, Fl_Color c) {
   fl_color(c);

documentation/src/drawing.dox

@@ -461,6 +461,12 @@ void fl_rect(int x, int y, int w, int h, Fl_Color c)
 \par
 Draw a 1-pixel border \e inside this bounding box.
 
+void fl_rounded_rect(int x, int y, int w, int h, int radius)
+void fl_rounded_rectf(int x, int y, int w, int h, int radius)
+
+\par
+Draw an outlined or filled rectangle with rounded corners.
+
 void fl_line(int x, int y, int x1, int y1) <br>
 void fl_line(int x, int y, int x1, int y1, int x2, int y2)
 

src/Fl_Graphics_Driver.cxx

@@ -455,6 +455,50 @@ void Fl_Graphics_Driver::rect(int x, int y, int w, int h) {}
 /** see fl_rectf() */
 void Fl_Graphics_Driver::rectf(int x, int y, int w, int h) {}
 
+void Fl_Graphics_Driver::_rbox(int fill, int x, int y, int w, int h, int r) {
+  static double lut[] = { 0.0, 0.07612, 0.29289, 0.61732, 1.0};
+  if (r == 5) r = 4;  // use only even sizes for small corners (STR #2943)
+  if (r == 7) r = 8;  // note: 8 is better than 6 (really)
+  double xd = x, yd = y, rd = (x+w-1), bd = (y+h-1);
+  double rr = r;
+  if (fill) begin_polygon(); else begin_loop();
+  // top left
+  transformed_vertex(xd+lut[0]*rr, yd+lut[4]*rr);
+  transformed_vertex(xd+lut[1]*rr, yd+lut[3]*rr);
+  transformed_vertex(xd+lut[2]*rr, yd+lut[2]*rr);
+  transformed_vertex(xd+lut[3]*rr, yd+lut[1]*rr);
+  transformed_vertex(xd+lut[4]*rr, yd+lut[0]*rr);
+  // top right
+  transformed_vertex(rd-lut[4]*rr, yd+lut[0]*rr);
+  transformed_vertex(rd-lut[3]*rr, yd+lut[1]*rr);
+  transformed_vertex(rd-lut[2]*rr, yd+lut[2]*rr);
+  transformed_vertex(rd-lut[1]*rr, yd+lut[3]*rr);
+  transformed_vertex(rd-lut[0]*rr, yd+lut[4]*rr);
+  // bottom right
+  transformed_vertex(rd-lut[0]*rr, bd-lut[4]*rr);
+  transformed_vertex(rd-lut[1]*rr, bd-lut[3]*rr);
+  transformed_vertex(rd-lut[2]*rr, bd-lut[2]*rr);
+  transformed_vertex(rd-lut[3]*rr, bd-lut[1]*rr);
+  transformed_vertex(rd-lut[4]*rr, bd-lut[0]*rr);
+  // bottom left
+  transformed_vertex(xd+lut[4]*rr, bd-lut[0]*rr);
+  transformed_vertex(xd+lut[3]*rr, bd-lut[1]*rr);
+  transformed_vertex(xd+lut[2]*rr, bd-lut[2]*rr);
+  transformed_vertex(xd+lut[1]*rr, bd-lut[3]*rr);
+  transformed_vertex(xd+lut[0]*rr, bd-lut[4]*rr);
+  if (fill) fl_end_polygon(); else fl_end_loop();
+}
+
+/** see fl_rrect() */
+void Fl_Graphics_Driver::rounded_rect(int x, int y, int w, int h, int r) {
+  _rbox(0, x, y, w, h, r);
+}
+
+/** see fl_rrectf() */
+void Fl_Graphics_Driver::rounded_rectf(int x, int y, int w, int h, int r) {
+  _rbox(1, x, y, w, h, r);
+}
+
 void Fl_Graphics_Driver::colored_rectf(int x, int y, int w, int h, uchar r, uchar g, uchar b) {
   color(r, g, b);
   rectf(x, y, w, h);

src/fl_rounded_box.cxx

@@ -23,35 +23,18 @@
 //  RS = max. corner radius
 //  BW = box shadow width
 
-#define RN 5
 #define RS (Fl::box_border_radius_max())
 #define BW (Fl::box_shadow_width())
 
-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 rs, rsy;
   rs = w*2/5; rsy = h*2/5;
   if (rs > rsy) rs = rsy; // use smaller radius
   if (rs > RS) rs = 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_r(x + offset[RN-i-1]*rs, y + offset[i] * rs);
-  for (i=0; i<RN; i++)
-    fl_vertex_r(x + offset[i]*rs, y + h-1 - offset[RN-i-1] * rs);
-  for (i=0; i<RN; i++)
-    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_r(x + w-1 - offset[i]*rs, y + offset[RN-i-1] * rs);
-  if (fill) fl_end_polygon(); else fl_end_loop();
+  if (fill)
+    fl_rounded_rectf(x, y, w, h, rs);
+  else
+    fl_rounded_rect(x, y, w, h, rs);
 }
 
 static void fl_rflat_box(int x, int y, int w, int h, Fl_Color c) {