[GRASS-dev] PNG driver - slow?

[Glynn Clements]

Glynn Clements wrote:

> > export GRASS_PNGFILE=/tmp/pokus.png
> > export GRASS_RENDER_IMMEDIATE=TRUE
> > 
> > time d.vect map=soils at PERMANENT
> > real    0m0.197s
> > user    0m0.166s
> > sys     0m0.019s
> > 
> > time d.vect map=soils at PERMANENT color=yellow fcolor=yellow cats=32 width=3
> > real    0m13.767s
> > user    0m13.611s
> > sys     0m0.098s
> > 
> > 
> > Why is the second case so slow? Is it a bug in PNG driver? What can I
> > do, so it is rendered faster?
> 
> My guess is the width=3.
> 
> The "thick line" code in the PNG driver is a truly awful hack (see
> store_xy() in lib/pngdriver/Draw_line.c).

I've replaced this with a more reasonable implementation.

However, note that the PNG driver doesn't have a proper polyline
implementation; it just draws each segment as a separate line. This is
fine for single-pixel lines, but for thicker lines the lack of proper
joins may be noticeable.

-- 
Glynn Clements <glynn at gclements.plus.com>