Add basic line drawing command

include/lib/gfx.h

 /*
  * Copyright (c) 2010 Travis Geiselbrecht
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files
  * (the "Software"), to deal in the Software without restriction,
  * including without limitation the rights to use, copy, modify, merge,
  * publish, distribute, sublicense, and/or sell copies of the Software,
  * and to permit persons to whom the Software is furnished to do so,
  * subject to the following conditions:
@@ skipping 59 matching lines @@
 
 // copy a rect from x,y with width x height to x2, y2
 void gfx_copyrect(gfx_surface *surface, uint x, uint y, uint width, uint height, uint x2, uint y2);
 
 // fill a rect within the surface with a color
 void gfx_fillrect(gfx_surface *surface, uint x, uint y, uint width, uint height, uint color);
 
 // draw a pixel at x, y in the surface
 void gfx_putpixel(gfx_surface *surface, uint x, uint y, uint color);
 
+// draw a single pixel line between x1,y1 and x2,y1
+void gfx_line(gfx_surface *surface, uint x1, uint y1, uint x2, uint y2, uint color);
+
 // clear the entire surface with a color
 static inline void gfx_clear(gfx_surface *surface, uint color)
 {
         surface->fillrect(surface, 0, 0, surface->width, surface->height, color);
 
         if (surface->flush)
                 surface->flush(0, surface->height-1);
 }
 
 // blend between two surfaces
@@ skipping 12 matching lines @@
 
 // free the surface
 // optionally frees the buffer if the free bit is set
 void gfx_surface_destroy(struct gfx_surface *surface);
 
 // utility routine to fill the display with a little moire pattern
 void gfx_draw_pattern(void);
 
 #endif