cameo: adding support for dril/mill substitutions (in progress)

- Makefile (OBJS): added shape.o
- README: added section for drill/mill substitutions
- lang.l, lang.y: added commands "drill", "empty", "mill", "remainder", and
  "reset"
- lang.y (clear_paths): moved freeing of all paths from "clean" to shared
  function clear_paths
- ops.h, ops.c (try_drill, try_mill): helper functions for "drill" and
  "mill" commands
- shape.h. shape.c (slot, circle): functions to generate toolpaths for
  basic shapes

cameo/shape.c

@@ -0,0 +1,83 @@
+/*
+ * shape.c - Toolpaths for basic shapes
+ *
+ * Written 2010 by Werner Almesberger
+ * Copyright 2010 Werner Almesberger
+ *
+ * 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.
+ */
+
+
+#include <math.h>
+
+#include "path.h"
+#include "shape.h"
+
+
+static struct path *path;
+
+
+static double arc2angle(double arc, double r)
+{
+	return acos(1-arc*arc/(r*r)/2);
+}
+
+
+static void half_circle(double cx, double cy, double rx, double ry, double z,
+    double s)
+{
+	double m[4];
+	double x = rx, y = ry, tmp;
+	double a;
+
+	m[0] = cos(s);
+	m[1] = -sin(s);
+	m[2] = -m[1];
+	m[3] = m[0];
+
+	for (a = 0; a < M_PI; a += s) {
+		path_add(path, cx+x, cy+x, z);
+		tmp = x*m[0]+y*m[1];
+		y = x*m[2]+y*m[3];
+		x = tmp;
+	}
+	path_add(path, cx-rx, cy-ry, z);
+}
+
+
+struct path *slot(double xa, double ya, double xb, double yb, double z,
+    double sr, double tr, double step)
+{
+	double dx = xb-xa;
+	double dy = yb-ya;
+	double s = arc2angle(step, sr);
+	double nx, ny;
+	double f;
+
+	f = (sr-tr)/hypot(dx, dy);
+	nx = -dy*f;
+	ny = dx*f;
+
+	path = path_new(tr);
+	half_circle(xa, ya, nx, ny, z, s);
+	half_circle(xb, yb, -nx, -ny, z, s);
+	path_add(path, xa+nx, ya+ny, z);
+	return path;
+}
+
+
+struct path *circle(double cx, double cy, double cz, double cr, double tr,
+    double step)
+{
+	double s = arc2angle(step, cr);
+	double a;
+
+	path = path_new(tr);
+	for (a = 0; a < 2*M_PI; a += s)
+		path_add(path, cx+(cr-tr)*cos(a), cy+(cr-tr)*sin(a), cz);
+	path_add(path, cx+(cr-tr), cy, cz);
+	return path;
+}