[Qgis-developer] Symbology api

[Martin Dobias]

Hi Vincent

On Fri, Oct 3, 2014 at 1:10 PM, Vincent Mora <vincent.mora at oslandia.com> wrote:
>
> We can use expressions to make the single symbol layer behave:
> - graduated : properties are continuous functions of attributes,
> - categorized or rule based : properties are discrete function of attributes
>
> The user interfaces for categorized, graduated, rule-based could remain the
> same, it's just that it would generate the expressions for the single symbol
> instead of configuring as specific class. Several categories could be
> defined to affect various parameters (color and size are the first use
> case).
>
> Can you tell me if the idea is sound ?

If I understand correctly, you propose to use single symbol renderer
with expressions (for color and for size) in places where we currently
use graduated/categorized renderers. Is that correct? If it is, how
would it handle the case where symbols of individual classes are
completely different? (not just varying in size/color)

It would be also good to check the impact on the rendering performance
- maybe if more than just few classes are used, the evaluation with
expressions could slow things down significantly. (the expression
engine could enjoy some performance improvements).

Regards
Martin