proper a4 sizing

envelope.asy

@@ -15,6 +15,7 @@ string envfmt = "C6";
 
 // debugging tool
 bool with_labels = true;
+bool force_a4 = true;
 
 
 // It is unpractical to try emulating second quadrant. We will work in the
@@ -22,9 +23,6 @@ bool with_labels = true;
 // the whole page). Therefore, the bottom edge of the page is at y=(210-297)
 int pgbot = pgw - pgh;
 
-//Force A4 size
-//draw((0,pgbot) -- (0, sqsz) -- (sqsz, sqsz) -- (sqsz, pgbot) -- cycle, invisible);
-
 // gimme a square?
 if (with_labels) draw(box((0,0), (sqsz, sqsz)), p=red);
 
@@ -116,3 +114,10 @@ draw(cb2 -- cl2);
 draw(cl1 -- (0, sqsz) -- ct2);
 draw(ct1 -- cr1);
 draw(cr2 -- (sqsz, 0) -- cb1);
+
+//Force A4 output size
+path a4_outline = (0,pgbot) -- (0, sqsz) -- (sqsz, sqsz) -- (sqsz, pgbot) -- cycle;
+if (force_a4) {
+	draw(a4_outline, invisible);
+	clip(a4_outline);
+}