Add functions for drawing rounded rectangles to the drawing api

[wyhinton]

Rounded rectangles have become a critical part of modern GUI design. Having a method for drawing them would be very handing. While it is nice to be able to set the global radius size for rounded frames, we might also want to have rounded frames with different radiuses. So, I think we could save people time by providing a method for drawing rounded rectangles a custom radius.

Such a method already exists in fl_rounded_box:

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();
}

[MatthiasWM]

With the current API, we do not have any additional parameters for box types besides the color. So storing the radius is only possible globally. It is however possible to add custom box types that could have different radii. See Fl::set_boxtype().

If that would solve the issue at hand, I'll take a look at the API and check if there is a way to make this option more reachable, maybe add an example.

[MatthiasWM]

See #553 for an implementation of fl_rrect(int x, int y, int w, int h, int radius) and fl_rrectf(int x, int y, int w, int h, int radius). If I don't get any negative comments, this will be in 1.4.0 in a day or two.

[Albrecht-S]

Please refer to my request for better names in #553 (comment).

[MatthiasWM]

Will fix that tomorrow

[MatthiasWM]

Renamed to fl_rounded_rect and fl_rounded_rectf