[Qgis-user] defining a variable width vector style

[Robin Paulson]

hi folks,
i'm trying to define a style which varies along the length of the line 
it's applied to, according to the position along that line. at the 
moment, as far as i can see, all styles are continuous along the line

so, for example let's say i want the line to be drawn as a cone, i would 
define the width of the style as proportional to the position on the 
line.

something like: line_width = line_pos x 0.1

at the start of the line, the width of the style should be 0m
1m along the line, the width should be 0.1m
1.5m along the line, the width should be 0.15m
10m along the line, the width should be 1m
and so on

any ideas about the best way to do this?

i considered adding a *lot* of nodes and varying the width in small 
steps at each node, but that would be clumsy and fiddly.

cheers,

-- 
robin