With the RULED I think you have to specify many points on the curve (i.e. many straight lines).
I think this is because the nodes of the polygon are listed twice - the first has a status code for visibility and the second has the height - so the mask for curves doesn't work.
I use a gosub routine like this to create the many nodes of a corner.
start_angle = 180
end_angle = 270
x_add = -x_val-x_squ_add
y_add = -y_val-y_squ_add
FOR angle = start_angle to end_angle step 10
PUT x_add+(rad*COS(angle)), y_add+(rad*SIN(angle)), z_status
I have never really used the TUBEA so can't comment on that one.
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