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there is already a ticket for this kind of issue. I have no time to check myself now, please have a look and eventually close the duplicate.

In any way I agree, selection for overlapped polygons can be better than it is now.

Giovanni Manghi wrote:

there is already a ticket for this kind of issue. I have no time to check myself now, please have a look and eventually close the duplicate.

In any way I agree, selection for overlapped polygons can be better than it is now.

Hi Giovanni,
I've found some tickets regarding the rendering of selected polygons but they were for older versions of QGIS. The closest tickets are #1509 and #4537. So I guess my ticket is a little bit different.
For QGIS 1.7.2 and the new symbology engine I haven't found anything like the one describe... The default render of selected unfilled polygons doesn't allow to see what's below so I guess the best way to fix this is when one chooses the unfilled type for polygon symbology, the selected renders only its border.

Giovanni Manghi wrote:

• semi-transparent selection color
• a new option in the QGIS general options, to let the user choose to add by default new polygons with a specified % of transparency
• I like also how uDIG behave when editing overlapping polygons, by removing the fill color (and adding the semi-transparent selection color).

The situation is much better than I though at the beginning, it would be just enough to add a default amount of transparency for both the selection color and the fill of polygons.

Setting the amount of transparency of the selection color is already available in QGIS***. It can be set in both the general options and in project properties. My opinion is that this should be set by default to a value around 180-200 (it is a alpha channel of a RGB scale).

This, coupled with a certain % of transparency for polygons fill, makes the the overall/out the box configuration much better when comes to layers with polygons completely/partially overlapped.

This way basically all the above issues would be "automatically fixed", regardless if they have fill or no fill:

• see polygons (or parts of) underlapped to other polygons

• see if/when they are both selected or if is selected just one

• also it would be "fixed" the issue of not seeing the polygon segments when editing polygons undelapped to others. And the gvSIG approach is not needed anyway because the node tool works only when clicking nearby a vertex.

A bonus help could come from having applied a particular border style for selected polygons and polygons being selected.

The only thing that I see it wouldn't be possible is to select from the canvas just a polygon that is completely underlapped to a another one, but in this case I guess that the right thing to do would be to select it (from the table of attributes), copy and paste (to make a copy above everything else) and then remove it.

I would like to have feedback from you and then propose this changes directly in the developers mailing list.

• and this by the way, answer the original ticket request

Yes, that would certainly do the trick. I agree that it would be a great help to apply a particular border style for selected polygons and polygons being selected. This combined with the a certain amount of transparency (or full transparency) of the selected polygons will help in deed to see all the features (vectors or rasters) below.

Giovanni Manghi wrote:

Giovanni Manghi wrote:

• semi-transparent selection color
• a new option in the QGIS general options, to let the user choose to add by default new polygons with a specified % of transparency
• I like also how uDIG behave when editing overlapping polygons, by removing the fill color (and adding the semi-transparent selection color).

The situation is much better than I though at the beginning, it would be just enough to add a default amount of transparency for both the selection color and the fill of polygons.

Setting the amount of transparency of the selection color is already available in QGIS***. It can be set in both the general options and in project properties. My opinion is that this should be set by default to a value around 180-200 (it is a alpha channel of a RGB scale).

This, coupled with a certain % of transparency for polygons fill, makes the the overall/out the box configuration much better when comes to layers with polygons completely/partially overlapped.

This way basically all the above issues would be "automatically fixed", regardless if they have fill or no fill:

• see polygons (or parts of) underlapped to other polygons

• see if/when they are both selected or if is selected just one

• also it would be "fixed" the issue of not seeing the polygon segments when editing polygons undelapped to others. And the gvSIG approach is not needed anyway because the node tool works only when clicking nearby a vertex.

A bonus help could come from having applied a particular border style for selected polygons and polygons being selected.

The only thing that I see it wouldn't be possible is to select from the canvas just a polygon that is completely underlapped to a another one, but in this case I guess that the right thing to do would be to select it (from the table of attributes), copy and paste (to make a copy above everything else) and then remove it.

I would like to have feedback from you and then propose this changes directly in the developers mailing list.

• and this by the way, answer the original ticket request

Hi guys,
There are some other problems related to this.

e.g. see the big polygon layer in the attached image. The symbols in the marker line symbol layer are yellow when selected, but the symbols in the fill pattern symbol layer retain their normal colour (the former behaviour is essentially the same as for the polyline layer). In my opinion the symbols in the fill pattern symbol layer should also be yellow, and there should not be a yellow fill for the whole polygon. i.e. the polygon fill style should be the same when selected as when not selected, and only the colours should change.

Now, look at the point layer in the top left, and imagine that "specify fill style for point markers" was implemented (it was implemented in old symbology, and there is a patch for new symbology). If you also applied my reasoning from above for point layers (fill style should be the same when selected), and changed the fill style of this symbol to "no brush", then there would be no way to distinguish the selected feature from all those that aren't selected, because (unlike polygon layers, as you can see in the bottom right) the pen colour does not change when selected, only the fill colour changes.

I guess there should thus be a standard "pen colour" AND a "brush colour" for selected features (possibly both yellow by default?), and all other aspects of rendering should not change (fill styles, symbols, line widths, transparency). But then there would still be no way to see selected features when they are hidden underneath other features!

Instead of all that complication, why not just render selected features in the same way that "identified" features are rendered?
i.e. Features would be rendered exactly the same whether or not they are selected. But the "identified" feature would also be redrawn over the top of all layers, with a standard outline and semi-transparent fill.
This seems to work very well for the identify tool. What do you think?

Having a semi-transparent color for selection (by default) seems like a good idea.

But using transparency for fill color by default also for rendering of unselected features should be avoided because it affects rendering speed. (With selection it is tolerable)

First of all we would need color dialogs to support alpha channel. Later we could add transparency for whole renderer (as with old symbology).