[GRASS-dev] Cairo monitor driver

Glynn Clements glynn at gclements.plus.com
Tue Oct 23 22:16:27 EDT 2007

Lars Ahlzen wrote:

> Lines 
> with odd widths are disproportinally common due, among other things, to 
> the fact that many d-modules do not offer control over the width of 
> lines in their output (and always draw 1-unit wide lines).

Actually, Cairo's default line width is 2.0 units:


All display modules will use this value until it's explicitly changed. 
The cairo driver should either explicitly change the line width to 1
at start-up, or interpret a line width of 0 as meaning 2 units rather
than 1.

There are only a handful of modules which actually change the line
width, namely d.graph, d.path and d.vect. All three modules set the
width using D_line_width() (which takes a double) and set it back
using R_line_width(0).

d.vect and d.graph set the width to a user-specified value, while
d.path sets it to 2 for "bold" lines.

Glynn Clements <glynn at gclements.plus.com>

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