From 5eed043d5330b4283a27b438f0c6f95a9e08504a Mon Sep 17 00:00:00 2001
From: Giles Bathgate <gilesbathgate@gmail.com>
Date: Tue, 22 Mar 2011 19:50:59 +0000
Subject: Optimised cylinder generation.

When the sides are vertical we can use 4 sided polygons instead of
triangles to define the sides, this reduces the facet count for the
sides of the cylinder by half.

diff --git a/src/primitives.cc b/src/primitives.cc
index d0cd1b5..a971683 100644
--- a/src/primitives.cc
+++ b/src/primitives.cc
@@ -377,17 +377,25 @@ sphere_next_r2:
 		
 		for (int i=0; i<fragments; i++) {
 			int j = (i+1) % fragments;
-			if (r1 > 0) {
+			if (r1 == r2) {
 				p->append_poly();
 				p->insert_vertex(circle1[i].x, circle1[i].y, z1);
 				p->insert_vertex(circle2[i].x, circle2[i].y, z2);
-				p->insert_vertex(circle1[j].x, circle1[j].y, z1);
-			}
-			if (r2 > 0) {
-				p->append_poly();
-				p->insert_vertex(circle2[i].x, circle2[i].y, z2);
 				p->insert_vertex(circle2[j].x, circle2[j].y, z2);
 				p->insert_vertex(circle1[j].x, circle1[j].y, z1);
+			} else {
+				if (r1 > 0) {
+					p->append_poly();
+					p->insert_vertex(circle1[i].x, circle1[i].y, z1);
+					p->insert_vertex(circle2[i].x, circle2[i].y, z2);
+					p->insert_vertex(circle1[j].x, circle1[j].y, z1);
+				}
+				if (r2 > 0) {
+					p->append_poly();
+					p->insert_vertex(circle2[i].x, circle2[i].y, z2);
+					p->insert_vertex(circle2[j].x, circle2[j].y, z2);
+					p->insert_vertex(circle1[j].x, circle1[j].y, z1);
+				}
 			}
 		}
 
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