[Qgis-developer] questions on rendering

[Marco Hugentobler]

Hi Mohammed

> How came this time gap?

A possible reason could be the following:
In QGIS, most point renderers do some caching of the point symbols as QImage. 
So in case you invoke a QPainter->drawCircle/drawRectangle etc. command for 
every point, it helps a lot do do the rasterisation only once.


Regards,
Marco
 

Am Dienstag, 27. September 2011, 16.18:25 schrieb Mohammed Rashad:
> Hi All,
> I am developing tiled vector rendering in OSSIM. I like the Qgis vector
> rendering system
> 
> point.shp contains 9,99,999 points which are generated by grass for using
> v.random and ~27MB in size
> roads.shp contains 2,28,068 linestrings and is ~50MB in size
> 
> these point.shp and roads.shp data gets rendered in ~10 sec
> 
> When I read vector using ogr and parse feature and draw point/linestring my
> application taking about 40 sec to render point.shp
> and
> 
> I am using Qt4 with QPainter not QGraphicsView
> 
> How came this time gap?
> 
> i see Rtree and pal libs in src/core source code
> Does they have any role in rendering?
> 
> Does QGIS Rendering uses threading?
> 
> How to get a minimal of QGIS code to hack it and build a new vector
> rendering because I need it to make it tiled rendering vectors?
> 
> How to improve performance in rendering without qgis?
> ---
> Regards,
>    Mohammed Rashad K M
>    M.S. (By Research) student
>    Lab for Spatial Informatics
>    Department of CSE
>    International Institute of Information Technology
>    Hyderabad, India