Thank you Stef,

the example helped me a lot to understand how to play with Athens. 

The solution is not what I am looking for. If someone starts to play with alpha canal, s/he will get unexpected results.

I have finally found an example in C language. It look like this:
-=-=-=-=-
cairo_set_line_width (cr, 0.1);
cairo_save (cr);
cairo_scale (cr, 1, 0.2);
cairo_arc (cr, 1.5, 1.5, 1, 0, 2 * M_PI);
cairo_restore (cr);
        cairo_set_source_rgba (cr, 0, 1, 0, 0.50);
cairo_stroke (cr);
-=-=-=-=-

I do not know how to write the same instructions with Athens. 

First, they draw one arc (cairo_arc (cr, 1.5, 1.5, 1, 0, 2 * M_PI);), I draw 4 arcs:
-=-=-=-=-
canvas
createPath: [ :builder | 
builder
absolute;
moveTo: 0 @ 0.5;
ccwArcTo: 0.5 @ 0.0 angle: 90 degreesToRadians;
ccwArcTo: 0.0 @ -0.5 angle: 90 degreesToRadians;
ccwArcTo: -0.5 @ 0.0 angle: 90 degreesToRadians;
ccwArcTo: 0 @ 0.5 angle: 90 degreesToRadians ].
-=-=-=-=-

Second, they set line width, before any other action (like cairo_save). I do:
-=-=-=-=-
canvas pathTransform scaleBy: 200 @ 50.
(can setStrokePaint: Color red) width: 0.1.
can drawShape:  path.
-=-=-=-=-

So, my result in Athens is like this:

Any idea? The example is explained here, C source code is here (by clicking on the image in the page).

Thank you,
Jura

El 12-04-2014, a las 4:01, Pharo4Stef <pharo4Stef@free.fr> escribi�:

AthensSceneView new
scene: [ :can |
| path |
path := can
createPath: [ :builder |
builder
absolute;
moveTo: 0 @ 0.5;
ccwArcTo: 0.5 @ 0.0 angle: 90 degreesToRadians;
ccwArcTo: 0.0 @ -0.5 angle: 90 degreesToRadians;
ccwArcTo: -0.5 @ 0.0 angle: 90 degreesToRadians;
ccwArcTo: 0 @ 0.5 angle: 90 degreesToRadians ].

can pathTransform
restoreAfter: [
can pathTransform scaleBy: 200 .
can
setPaint: Color red ;
drawShape:  path.
"(athensCanvas setStrokePaint: strokePaint)
width: (self strokeWidth / self scale) asFloat."
can drawShape:  path.].
can pathTransform
restoreAfter: [
can pathTransform scaleBy: 190 .
can
setPaint: Color blue ;
drawShape:  path.
"(athensCanvas setStrokePaint: strokePaint)
width: (self strokeWidth / self scale) asFloat."
can drawShape:  path

]
] ;
openInWindow


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