[Qgis-developer] Rule based renderer and colours

[Martin Dobias]

Hi Chris

On Sat, Apr 13, 2013 at 8:57 AM, Chris Crook <ccrook at linz.govt.nz> wrote:
> Hi
>
> I really like the rule based renderer.  One thing that doesn't seem easy though is to use the "colour" data defined property, as it isn't clear (and possibly not easy) to generate an expression for a colour.
>
> I am thinking it would be really useful to have a "Colour" section in the function list, with at least two functions - rgb(x,y,z), and ramp(name,value) (value from 0 to 1, or 0 to 100?).  Possibly one more - rgba(x,y,z,a).  Then it would be very easy to build colours from data.
>
> I'm guessing this would be easy to do - any takers?  or pointers to where to implement it?

The implementation should be quite straightforward - you can have a
look at QgsExpression class and the built-in functions it provides.
Creating a function that takes three integers and composes a string
from them should be really just few lines of code.

Martin