demo: Add average strip length to demo output

This is a similar efficiency measure to strip index count and can be
used to compare the results to other published algorithms. For
simplicity, we only measure the strip length when restart indices are
used; the results should not depend on whether that's the case (compared
to strip index percentage which does).

demo/main.cpp

@@ -865,6 +865,10 @@ void stripify(const Mesh& mesh, bool use_restart, char desc)
 	strip.resize(meshopt_stripify(&strip[0], &mesh.indices[0], mesh.indices.size(), mesh.vertices.size(), restart_index));
 	double end = timestamp();
 
+	size_t restarts = 0;
+	for (size_t i = 0; i < strip.size(); ++i)
+		restarts += use_restart && strip[i] == restart_index;
+
 	Mesh copy = mesh;
 	copy.indices.resize(meshopt_unstripify(&copy.indices[0], &strip[0], strip.size(), restart_index));
 	assert(copy.indices.size() <= meshopt_unstripifyBound(strip.size()));
@@ -877,9 +881,10 @@ void stripify(const Mesh& mesh, bool use_restart, char desc)
 	meshopt_VertexCacheStatistics vcs_amd = meshopt_analyzeVertexCache(&copy.indices[0], mesh.indices.size(), mesh.vertices.size(), 14, 64, 128);
 	meshopt_VertexCacheStatistics vcs_intel = meshopt_analyzeVertexCache(&copy.indices[0], mesh.indices.size(), mesh.vertices.size(), 128, 0, 0);
 
-	printf("Stripify%c: ACMR %f ATVR %f (NV %f AMD %f Intel %f); %d strip indices (%.1f%%) in %.2f msec\n",
+	printf("Stripify%c: ACMR %f ATVR %f (NV %f AMD %f Intel %f); %.1f run avg, %d strip indices (%.1f%%) in %.2f msec\n",
 	    desc,
 	    vcs.acmr, vcs.atvr, vcs_nv.atvr, vcs_amd.atvr, vcs_intel.atvr,
+	    use_restart ? double(strip.size() - restarts) / double(restarts + 1) : 0,
 	    int(strip.size()), double(strip.size()) / double(mesh.indices.size()) * 100,
 	    (end - start) * 1000);
 }