1 files changed, 59 insertions, 0 deletions
diff --git a/plug-ins/selection-to-path/edge.h b/plug-ins/selection-to-path/edge.h
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+++ b/plug-ins/selection-to-path/edge.h
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+/* edge.h: declarations for edge traversing.
+ *
+ * Copyright (C) 1992 Free Software Foundation, Inc.
+ *
+ * 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 3, 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, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef EDGE_H
+#define EDGE_H
+
+#include "bitmap.h"
+
+/* We consider each pixel to consist of four edges, and we travel along
+   edges, instead of through pixel centers.  This is necessary for those
+   unfortunate times when a single pixel is on both an inside and an
+   outside outline.
+
+   The numbers chosen here are not arbitrary; the code that figures out
+   which edge to move to depends on particular values.  See the
+   `TRY_PIXEL' macro in `edge.c'.  To emphasize this, I've written in the
+   numbers we need for each edge value.  */
+
+typedef enum
+{
+  top = 1, left = 2, bottom = 3, right = 0, no_edge = 4
+} edge_type;
+
+/* This choice is also not arbitrary: starting at the top edge makes the
+   code find outside outlines before inside ones, which is certainly
+   what we want.  */
+#define START_EDGE  top
+
+
+/* Return the next outline edge on B in EDGE, ROW, and COL.  */
+extern void next_outline_edge (edge_type *edge,
+	   	   	       unsigned *row, unsigned *col);
+
+/* Return the next edge after START on the pixel ROW/COL in B that is
+   unmarked, according to the MARKED array.  */
+extern edge_type next_unmarked_outline_edge (unsigned row, unsigned col,
+                                             edge_type start,
+                                             bitmap_type marked);
+
+/* Mark the edge E at the pixel ROW/COL in MARKED.  */
+extern void mark_edge (edge_type e, unsigned row, unsigned col,
+                       bitmap_type *marked);
+
+#endif /* not EDGE_H */