Incremental rendering of features does not work when render cache is used

[jpalmer]

r11831 introduced the feature to cache rendering whenever possible. However this new functionality has disabled the number of features to draw before updating the display.

[lutra]

confirmed also under linux with trunk. Is this on purpose?

[smizuno]

Actually, it is partially working on the initial rendering - after a layer is drawn, it is displayed. This appears to be an unintended consequence.

However, the point of caching is to speed up redrawing the map if it is not necessary to re-render a layer, as when a layer is disabled/enabled for view and the extent hasn't changed, so I don't see a reason for incremental drawing at all.

I would recommend when render caching is enabled, incremental drawing not be used during rendering and be disabled in Settings|Options to indicate that it is not available.