MetaFun - Pragma ADE

90
sample (z1 {curl 0} .. z2 .. {curl 0} z3, .625red) ;
sample (z1 {curl infinity} .. z2 .. {curl infinity} z3, .625yellow) ;
sample (z1 {curl 1} .. z2 .. {curl 1} z3, .625white) ;
It may sound strange, but internally METAPOST can handle larger values than infinity.
sample (z1 {curl infinity} .. z2 .. {curl infinity} z3, .625red) ;
sample (z1 {curl 4infinity} .. z2 .. {curl 4infinity} z3, .625yellow) ;
sample (z1 {curl 8infinity} .. z2 .. {curl 8infinity} z3, .625white) ;
Although this is quite certainly undefined behaviour, interesting effects can be achieved. When
you turn off METAPOST's first stage overflow catcher by setting warningcheck to zero, you can go
upto 8 times infinity, which, being some 2 15 , is still far from what today's infinity is supposed to
be.
As the built--in METAPOST command .. accepts the curl and tension directives as described in
this section, you will now probably understand the following plain METAPOST definitions:
def -- = {curl 1} .. {curl 1} enddef ;
def --- = .. tension infinity .. enddef ;
def ... = .. tension atleast 1 .. enddef ;
These definitions also point out why you cannot add directives to the left or right side of --, --and
...: they are directives themselves!
2.7 Transformations
A transform is a vector that is used in what is called an affine transformation. To quote the META
POST manual:
“If p = (px,py) is a pair and T is a transform, then p transform T is a pair of the form:
(tx + txxpx + txypy,ty + tyxpx + tyypy)
where the six numeric quantities (tx,ty,txx,txy,tyx,tyy) determine T.”
A few more details Transformations