Adding an API for developing Magic tools as plug-ins. (e.g., '.so'

shared objects under Linux)
Ported (most of) 'Negative' magic tool to Magic tool plug-in system.

magic/src/negative.c

@@ -0,0 +1,111 @@
+#include <stdio.h>
+#include <string.h>
+#include "SDL_image.h"
+#include "magic_helpers.h"
+
+void init()
+{
+  printf("negative plugin initializing\n");
+}
+
+int get_tool_count(void)
+{
+  printf("negative tool reporting tool count: 1\n");
+  return(1);
+}
+
+SDL_Surface * get_icon(int which)
+{
+  printf("Loading icon: " DATA_PREFIX "/images/magic/negative.png\n");
+  return(IMG_Load(DATA_PREFIX "/images/magic/negative.png"));
+}
+
+char * get_name(int which)
+{
+  /* Only 1 tool; ignoring 'which' */
+
+  return(strdup(gettext("Negative")));
+}
+
+char * get_description(int which)
+{
+  /* Only 1 tool; ignoring 'which' */
+
+  return(strdup(gettext("Click and move the mouse around to draw a negative.")));
+}
+
+void drag(int which, SDL_Surface * canvas, SDL_Surface * last, int ox, int oy, int x, int y);
+
+void click(int which, SDL_Surface * canvas, SDL_Surface * last, int x, int y)
+{
+/*
+  SDL_Rect src, dest;
+
+  src.x = x - 12;
+  src.y = y - 12;
+  src.w = 16;
+  src.h = 16;
+
+  dest.x = x - 8;
+  dest.y = y - 8;
+  dest.w = 16;
+  dest.h = 16;
+
+  SDL_BlitSurface(last, &src, canvas, &dest);
+*/
+
+  drag(which, canvas, last, x, y, x, y);
+}
+
+void drag(int which, SDL_Surface * canvas, SDL_Surface * last, int ox, int oy, int x, int y)
+{
+  int xx, yy;
+  Uint8 r, g, b;
+  void (*putpixel) (SDL_Surface *, int, int, Uint32) =
+    MAGIC_putpixels[canvas->format->BytesPerPixel];
+  Uint32(*getpixel_last) (SDL_Surface *, int, int);
+
+  getpixel_last = MAGIC_getpixels[last->format->BytesPerPixel];
+
+
+  SDL_LockSurface(last);
+  SDL_LockSurface(canvas);
+
+  for (yy = y - 16; yy < y + 16; yy++)
+  {
+    for (xx = x - 16; xx < x + 16; xx++)
+    {
+      if (MAGIC_in_circle(xx - x, yy - y, 16))
+      {
+        SDL_GetRGB(getpixel_last(last, xx, yy), last->format, &r, &g, &b);
+
+        r = 0xFF - r;
+        g = 0xFF - g;
+        b = 0xFF - b;
+
+        putpixel(canvas, xx, yy, SDL_MapRGB(canvas->format, r, g, b));
+      }
+    }
+  }
+  
+  SDL_UnlockSurface(canvas);
+  SDL_UnlockSurface(last);
+}
+
+void shutdown()
+{
+  printf("negative plugin shutting down\n");
+}
+
+void set_color(Uint8 r, Uint8 g, Uint8 b)
+{
+  /* Doesn't use color; ignoring */
+}
+
+int requires_colors(int which)
+{
+  /* (Only 1 tool; ignoring 'which') */
+
+  return 0;  // Don't need a color palette
+}
+