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

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Werner Almesberger 2011-07-23 15:23:30 -03:00
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@ -17,6 +17,10 @@ http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/cad/te
New findings and hypotheses 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 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 Before: 4901.0 4904.4 1.5 8362 3183
After: 316.3 315.9 0.3 2942 1473 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 rendering, a marked improvement from the previous factor of 57. The
resulting mesh is now less than half the size of the mesh generated resulting mesh is now less than half the size of the mesh generated
by OpenSCAD. by OpenSCAD.
@ -43,16 +47,16 @@ Furthermore, the model is much easier to design and more
understandable without these extra tolerances. understandable without these extra tolerances.
Context: preventing artefacts Background: preventing artefacts
----------------------------- --------------------------------
When subtracting volumes from each other, surfaces that coincide in 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. as arbitrarily thin artefacts.
This 2D example illustrates the effect: 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 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 different color without actually removing them is caused by using
OpenGL emulation in Mesa. This needs further investigation. 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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