Graphics Programs Reference
In-Depth Information
Simple Two-Dimensional Patches
To define a simple patch, specify the
x
and
y
coordinates and the face
colour:
2
1
x=[0110];
y=[0011];
patch(x,y,'y')
axis([-2 2 -2 2])
0
−1
−2
−2
−1
0
1
2
The colour of the edge is black by default. The
patch
function automat-
ically closes the edge if the last vertex is not the same as the first vertex.
Patches are usually defined with noncrossing boundaries, but boundaries
can cross if required:
1
0.8
x(4) = 2; y(4) = .5;
clf
patch(x,y,'y')
0.6
0.4
0.2
0
0
0.5
1
1.5
2
(The
patch
command is a low-level command, which means that it gen-
erates a patch in the current axes without first clearing the axes. That
is the reason for the
clf
above.)
Between patches whose boundaries cross and those whose boundaries
do not cross are the patches whose boundaries “touch”. These can be
used to create patches with holes:
1
x = [0 .5 .5 .4 .5 .6 .5 .5 1 .5];
y = [0 0 .1 .2 .3.2 .1 0 0 1];
clf
h = patch(x,y,'y');
0.8
0.6
0.4
0.2
0
0
0.5
1
The tell-tale line between the outer boundary and the hole can be deleted
by making it either invisible or the same colour as the face:
1
0.8
0.6
set(h,'edgecolor','none')
0.4
0.2
0
0
0.5
1
(The command
set(h,'edgecolor','y')
achieves the same effect.)
But it would be nice to leave the edge boundary drawn around the
shading; you just have to plot a line with the right points:
