cad/test2/README: added more results and cleaned up the text

cad/test2/README

@@ -17,6 +17,10 @@ http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/cad/te
 New findings and hypotheses
 ===========================
 
+The first test revealed several problems in both OpenSCAD and
+Cadmium. It turned out that most of them could be resolved by making
+small changes to the models.
+
 
 The road to hell is paved with good intentions
 ----------------------------------------------
@@ -34,7 +38,7 @@ This is a comparison of run time (in seconds) and mesh size:
 Before:         4901.0  4904.4     1.5  8362    3183
 After:           316.3   315.9     0.3  2942    1473
 
-This makes Cadmium only about 3.7 times slower than OpenSCAD's CGAL
+This makes Cadmium only about 4-5 times slower than OpenSCAD's CGAL
 rendering, a marked improvement from the previous factor of 57. The
 resulting mesh is now less than half the size of the mesh generated
 by OpenSCAD.
@@ -43,16 +47,16 @@ Furthermore, the model is much easier to design and more
 understandable without these extra tolerances.
 
 
-Context: preventing artefacts
+Background: preventing artefacts
------------------------------
+--------------------------------
 
 When subtracting volumes from each other, surfaces that coincide in
-both the original volume and the one subtracted from it, can remain
+both the original volume and the one subtracted from it can remain
 as arbitrarily thin artefacts.
 
 This 2D example illustrates the effect:
 
-- given an original shape A like this
+- given an original shape like this
 
   +---------------+
   |               |
@@ -99,16 +103,21 @@ This 2D example illustrates the effect:
          +---------+
 
 
-Artefacts in OpenSCAD's mesh may also be rounding errors
+Artefacts in OpenSCAD's mesh were rounding errors
---------------------------------------------------------
+-------------------------------------------------
 
-The artefacts found in the mesh produced by OpenSCAD may also be
+The artefacts found in the mesh produced by OpenSCAD were also caused
-caused from rounding errors. In this case, the problem would be parts
+by rounding errors. In this case, the problem were parts that were
-that are fused along a common surface. As in the above example, this
+fused along a common surface. As in the above example, this could be
-could be solved by making the parts overlap a little.
+solved by making the parts overlap a little.
 
-Whether this is truly the source of the artefacts still needs to be
+This change affected the rendering performance as follows:
-verified.
+
+                real    user    system  faces   vertices
+Before:		  85.5	  85.0	   0.4	7798	3351
+After:		  68.8	  65.4	   0.5	6508	3258
+
+The resulting mesh looks as good as the one generated by Cadmium.
 
 
 OpenCSG problems may be an OpenGL compatibility issue
@@ -118,4 +127,30 @@ It could be that OpenCSG showing volumes to be removed just with a
 different color without actually removing them is caused by using
 OpenGL emulation in Mesa. This needs further investigation.
 
+
+Conclusion
+==========
+
+The model used in the first test contained constructs that were meant
+to help avoid ambiguous situations. It turned out that Cadmium did
+not need this "help" and removing the constructs substantially
+increased the rendering speed.
+
+OpenSCAD is the exact opposite: it produces clearly visible
+artefacts in ambiguous cases and rendering speed also benefits from
+manual resolution of these issues. The cost of doing so is an
+increase of the complexity of the model.
+
+Performance after the model changes (times are in seconds):
+
+                real    user    system  faces   vertices
+OpenSCAD:	  68.8	  65.4	   0.5	6508	3258
+Cadmium:	 316.3	 315.9	   0.3	2942	1473
+
+The sources of the models used are in
+http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/cad/test2/
+
+The meshes can be downloaded from
+http://downloads.qi-hardware.com/people/werner/cad/test2/
+
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