Elevate "Fill" from Magic Tool to real Tool

Replace the somewhat-recently-added "nothing" item in the tool bar
with the "Fill" tool, which has been converted back from a Magic tool
to a regular tool.

Also, change bash "==" to sh "=" in "if [ ... ]" tests in Makefile.

Also, link to math library (via "-lm") to make sure "max()" is available to
magic tools.

Also, add missing mention of "--newcolorslast" and "--newcolorsfirst" to manpage.

src/fill.c

@@ -0,0 +1,160 @@
+/*
+  fill.c
+
+  Fill tool
+  Tux Paint - A simple drawing program for children.
+
+  Copyright (c) 2002-2019 by Bill Kendrick and others; see AUTHORS.txt
+  bill@newbreedsoftware.com
+  http://www.tuxpaint.org/
+
+  Flood fill code based on Wikipedia example:
+  http://www.wikipedia.org/wiki/Flood_fill/C_example
+  by Damian Yerrick - http://www.wikipedia.org/wiki/Damian_Yerrick
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+  (See COPYING.txt)
+
+  Last updated: September 12, 2019
+  $Id$
+*/
+
+#include <stdio.h>
+#include <string.h>
+#include "fill.h"
+#include "rgblinear.h"
+#include "playsound.h"
+#include "pixels.h"
+
+
+/* Local function prototypes: */
+
+int colors_close(SDL_Surface * canvas, Uint32 c1, Uint32 c2);
+
+
+int colors_close(SDL_Surface * canvas, Uint32 c1, Uint32 c2)
+{
+  Uint8 r1, g1, b1, r2, g2, b2;
+
+  if (c1 == c2)
+    {
+      /* Get it over with quick, if possible! */
+
+      return 1;
+    }
+  else
+    {
+      double r, g, b;
+
+      SDL_GetRGB(c1, canvas->format, &r1, &g1, &b1);
+      SDL_GetRGB(c2, canvas->format, &r2, &g2, &b2);
+
+      // use distance in linear RGB space
+      r = sRGB_to_linear_table[r1] - sRGB_to_linear_table[r2];
+      r *= r;
+      g = sRGB_to_linear_table[g1] - sRGB_to_linear_table[g2];
+      g *= g;
+      b = sRGB_to_linear_table[b1] - sRGB_to_linear_table[b2];
+      b *= b;
+
+      // easy to confuse:
+      //   dark grey, brown, purple
+      //   light grey, tan
+      //   red, orange
+      return r + g + b < 0.04;
+    }
+}
+
+
+void do_flood_fill(SDL_Surface * canvas, int x, int y, Uint32 cur_colr, Uint32 old_colr, int * x1, int * y1, int * x2, int * y2)
+{
+  int fillL, fillR, i, in_line;
+  static unsigned char prog_anim;
+
+
+  if (cur_colr == old_colr || colors_close(canvas, cur_colr, old_colr))
+    return;
+
+  if (y < *y1)
+    {
+      *y1 = y;
+    }
+  if (y > *y2)
+    {
+      *y2 = y;
+    }
+
+
+  fillL = x;
+  fillR = x;
+
+  prog_anim++;
+  if ((prog_anim % 4) == 0)
+    {
+      /* FIXME: api->update_progress_bar(); */
+      playsound(canvas, 1, SND_FILL, 1, x, SNDDIST_NEAR);
+    }
+
+
+  /* Find left side, filling along the way */
+
+  in_line = 1;
+
+  while (in_line)
+    {
+      putpixels[canvas->format->BytesPerPixel] (canvas, fillL, y, cur_colr);
+      fillL--;
+
+      in_line = (fillL < 0) ? 0 : colors_close(canvas, getpixels[canvas->format->BytesPerPixel] (canvas, fillL, y), old_colr);
+    }
+
+  if (fillL < *x1)
+    {
+      *x1 = fillL;
+    }
+
+  fillL++;
+
+  /* Find right side, filling along the way */
+
+  in_line = 1;
+  while (in_line)
+    {
+      putpixels[canvas->format->BytesPerPixel] (canvas, fillR, y, cur_colr);
+      fillR++;
+
+      in_line = (fillR >= canvas->w) ? 0 : colors_close(canvas, getpixels[canvas->format->BytesPerPixel] (canvas, fillR, y), old_colr);
+    }
+
+  if (fillR > *x2)
+    {
+      *x2 = fillR;
+    }
+
+  fillR--;
+
+
+  /* Search top and bottom */
+
+  for (i = fillL; i <= fillR; i++)
+    {
+      if (y > 0 && colors_close(canvas, getpixels[canvas->format->BytesPerPixel] (canvas, i, y - 1), old_colr))
+        do_flood_fill(canvas, i, y - 1, cur_colr, old_colr, x1, y1, x2, y2);
+
+      if (y < canvas->h && colors_close(canvas, getpixels[canvas->format->BytesPerPixel] (canvas, i, y + 1), old_colr))
+        do_flood_fill(canvas, i, y + 1, cur_colr, old_colr, x1, y1, x2, y2);
+    }
+}
+