===== Drawing rounded rectangles =====

//by Richard Russell, January 2021//

Neither //BBC BASIC for Windows// nor //BBC BASIC for SDL 2.0// supports drawing anti-aliased **rounded rectangles** (that is, boxes with radiused corners).  Fortunately it is easy enough to decompose that shape into simpler components (straight lines and 90° arcs) which can be drawn using the supplied anti-aliased graphics libraries (**gdiplib.bbc** or **aagfxlib.bbc** respectively).

Here are the two routines.  The parameters are the **x and y coordinates** of the bottom left-hand corner, the **width and height**, the corner **radius** (all in BBC BASIC graphics units), the line **thickness** (pixels) and the **colour**. Note that the colour value has a different format depending on the library, &AARRGGBB for **gdiplib** and &AABBGGRR for **aagfxlib**.

BB4W version:

<code bb4w>
      DEF PROCroundrect(x, y, w, h, r, t, C%)
      LOCAL pen%
      pen% = FN_gdipcreatepen(C%, 0, t)
      PROC_gdiparc(pen%, x+r,   y+h-r, r, r, 180, 90)
      PROC_gdiparc(pen%, x+w-r, y+h-r, r, r, 270, 90)
      PROC_gdiparc(pen%, x+r,   y+r,   r, r, 90,  90)
      PROC_gdiparc(pen%, x+w-r, y+r,   r, r, 0,   90)
      r -= 0.3 : REM overlap 0.15 pixels
      PROC_gdipline(pen%, x+r, y+h, x+w-r, y+h)
      PROC_gdipline(pen%, x+r, y,   x+w-r, y)
      PROC_gdipline(pen%, x,   y+r, x,   y+h-r)
      PROC_gdipline(pen%, x+w, y+r, x+w, y+h-r)
      PROC_gdipdeletepen(pen%)
      ENDPROC
</code>

BBCSDL version:

<code bb4w>
      DEF PROCroundrect(x, y, w, h, r, t, C%)
      PROC_aaarc(x+r,   y+h-r, r, r, 180, 90, t, C%, 0)
      PROC_aaarc(x+w-r, y+h-r, r, r, 270, 90, t, C%, 0)
      PROC_aaarc(x+r,   y+r,   r, r, 90,  90, t, C%, 0)
      PROC_aaarc(x+w-r, y+r,   r, r, 0,   90, t, C%, 0)
      r -= 0.3 : REM overlap 0.15 pixels
      PROC_aaline(x+r, y+h, x+w-r, y+h, t, C%, 0)
      PROC_aaline(x+r, y,   x+w-r, y,   t, C%, 0)
      PROC_aaline(x,   y+r, x,   y+h-r, t, C%, 0)
      PROC_aaline(x+w, y+r, x+w, y+h-r, t, C%, 0)
      ENDPROC
</code>