How to make pictures using postscript programs (part 8)
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Another part of the current graphics state is the clipping region. 
The clipping region is where your drawing commands are actually executed;
every part of your picture that falls outside the clipping region is not 
displayed. Initially, the clipping region is the entire plane (or perhaps
the bounding box), and you can make it smaller by the command clip.
clip takes your current path, which must be closed, like fill, and establishes 
that as new clipping path. Each further restriction of the clipping region
makes it smaller, so additional clipping regions are intersected with 
the previous clipping region. If you need to go back to a larger clipping 
region, you have to save it, with gsave, and the restore it when needed.
The previous clipping region is not moved by later coordinate transformations,
it describes a fixed region on paper.
------------------------Example 16-------------------------------------------
%!PS-Adobe-2.0
%%BoundingBox: 0 0 400 400

newpath 200 200 170 0 360 arc closepath clip %clips the following to a circle
0 4 400 {newpath 0 0 moveto 400 0 lineto stroke
0 4 translate} for

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------------------------Example 17-------------------------------------------
%!PS-Adobe-2.0
%%BoundingBox: 0 0 300 200

gsave
50 50 translate
newpath  0 0 moveto 100 0 lineto 100 100 lineto 0 100 lineto
closepath clip %clips the following to a square
0 4 200 {newpath -100 0 moveto 100 100 rlineto stroke %Diagonal /
4 0 translate} for
grestore
gsave
150 50 translate
newpath  0 0 moveto 100 0 lineto 100 100 lineto 0 100 lineto
closepath clip %clips the following to a square
0 4 200 {newpath 0 0 moveto -100 100 rlineto stroke %Diagonal \
4 0 translate} for
grestore

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------------------------Example 18-------------------------------------------
%!PS-Adobe-2.0
%%BoundingBox: 0 0 300 300

/petal {gsave newpath 100 0 moveto
50 -86.6 100 60 120 arc 50 86.6 100 240 300 arc closepath 
gsave stroke grestore clip 
1.0 -0.1 0 {/c exch def newpath 0 -50 moveto 0 50 lineto 100 c mul 50 lineto
100 c mul -50 lineto closepath 
1.0 c 0.1 setrgbcolor fill} for
grestore } def

150 150 translate
1 1 6 {petal 60 rotate} for

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