drl2gp.c: added milling of slots (more to come)

drl2gp/drl2gp.c

@@ -137,9 +137,51 @@ static void header(void)
 }
 
 
+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 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) {
+		printf("%f %f %f\n", cx+x, cy+y, -depth);
+		tmp = x*m[0]+y*m[1];
+		y = x*m[2]+y*m[3];
+		x = tmp;
+	}
+	printf("%f %f %f\n", cx-rx, cy-ry, -depth);
+}
+
+
 static void slot(double xa, double ya, double xb, double yb, double d)
 {
+	double dx = xb-xa;
+	double dy = yb-ya;
+	double cr = d/2;
+	double tr = d0/2;
+	double s = arc2angle(MAX_STEP, cr);
+	double nx, ny;
+	double f;
+
 	assert(mill);
+	f = (cr-tr)/hypot(dx, dy);
+	nx = -dy*f;
+	ny = dx*f;
+
+	half_circle(xa, ya, nx, ny, s);
+	half_circle(xb, yb, -nx, -ny, s);
+	printf("%f %f %f\n\n", xa+nx, ya+ny, -depth);
 }
 
 
@@ -147,7 +189,7 @@ static void circle(double cx, double cy, double d)
 {
 	double cr = d/2;
 	double tr = d0/2;
-	double s = acos(1-MAX_STEP*MAX_STEP/(cr*cr)/2);
+	double s = arc2angle(MAX_STEP, cr);
 	double a;
 
 	assert(mill);