The plclear() method does not seem to work for either xwin or tk. As a test I modified the x09c.c example:
pllab("X Coordinate", "Y Coordinate", "Streamlines of flow");
pl_setcontlabelparam(0.006, 0.3, 0.1, 0);
/* Plot using 1d coordinate transform */
plclear(); // Added this line.
plenv(-1.0, 1.0, -1.0, 1.0, 0, 0);
And plclear did not do anything. Am I doing something wrong or is this a bug?
You could use pladv(), which advances to the next page and clears it. This is how it is normally done in the examples. It still a bug though it seems.