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It is incredibly helpful to be able to select things by their trait (i.e. Select Similar > Normals).

Is there a way to deselect geometry in the same way?

Using the image below as an example:

  • I want to flip the red normals on the power button, but all of the geometry is connected so I can't use Connect Linked
  • It would be helpful if I could simply drag a large select brush over the whole area and then de-select the normals facing in the other direction, leaving me with only the normals I want to flip

Is this possible?

enter image description here

Note: I know various ways to get the job done, but in particular I'm interested in knowing if this specific way is on the table, as it seems the most streamlined.

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  • $\begingroup$ So if you are not interested in other possible ways to flip them because you know various ways (for example, Shift+N to Recalculate Normals should work since they are all connected), but want to select them by their normal direction - then probably this is not the best object as example for that. Because the main face is (almost) perpendicular to the side face bordering the blue area, and if you had to use a great tolerance to select them, then blue faces will be selected, too... oh, but I thought of a way, I'll write an answer for that. $\endgroup$ Oct 18, 2023 at 10:00
  • $\begingroup$ Thanks @GordonBrinkmann I actually didn't realize that Recalculate Normals would work this way, so that's helpful indeed ;) $\endgroup$ Oct 18, 2023 at 16:47

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What you can do is use the Select Linked tool. In Edit Mode make sure everything is deselected and you are in Face Select mode by pressing 3 or the button in the top menu (selecting vertices or edges would work too, but faces is the easiest way especially when you don't want to specifically select vertices/edges).

Then hold your mouse above a red face and press L. Now all faces that are connected to this one will be selected (even blue ones) because by default the selected is delimited by Seam and I assume for now you don't have any.

select linked default

But if you switch from Seam to Normal in the tool options at the bottom left of the viewport, then only the red ones are selected.

select link normal

If there are more red areas that have no connection to the first selected, just hover your mouse over them and press L again - no need to hold Shift, the Select Linked tool automatically adds to the selection, it does not replace the previous.

Another way for several red "island" connected to a blue mesh would be, to use Select Linked on the blue area and then invert the selection afterwards with Ctrl+I.

The checkbox Deselect in the options can do the following: let's say the complete mesh is selected. If you hold your mouse over a red area and press L, with Normal enabled and you check Deselect, then the (connected) red faces will be deselected from the selection. However, the Deselect has to be activated each time after pressing L.

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  • $\begingroup$ Thanks Gordon! This is a great solution, except in situations like mine where there are multiple areas where the normals are flipped, this will select all of the similar normals. I know you can at that point just manually go over the areas with the select brush and deselect what you don't want, but I was just looking specifically for a way to 'de-select similar' in the same way you can 'select similar' (e.g. in cases where you have one giant mess of geometry that needs to be cleaned up, i.e. models from Turbosquid), which unfortunately seems there is no elegant way to do. $\endgroup$ Oct 18, 2023 at 16:56
  • $\begingroup$ @GlenCandle I'm not sure if I understand what you mean. This method will only select connected flipped normals, not "all of the similar normals". $\endgroup$ Oct 19, 2023 at 6:55
  • $\begingroup$ Right, but unless I'm confused (which is very likely!) if there are multiple flipped normals on the same geometry, all connected, then you'd be selecting more than just the one area in question $\endgroup$ Oct 19, 2023 at 20:18
  • $\begingroup$ Maybe I'm confused or your example pic is not the best to illustrate the problem. You wrote in the question: "I want to flip the red normals on the power button, but all of the geometry is connected so I can't use Connect Linked". To me this sounds as if you want to flip all red ones, but cannot select them with Select Linked because they are connected to the rest of the blue geometry. If red ones that should be flipped are connected to other red ones that should not be flipped, I don't know how Blender should tell the difference between them to automatically select correctly. $\endgroup$ Oct 19, 2023 at 22:36
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    $\begingroup$ @GlenCandle No problem, it's not about getting reputation for me, it's just that I want users looking for an answer to find a working one when it exists ;) Maybe I'll edit my answer later showing that you can select multiple "red islands" one by one with this method. $\endgroup$ Oct 20, 2023 at 6:04
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No, unfortunately this is not possible. Select Similar operators do not have this functionality. You can only invert selection( Ctrl + I ) once it's selected with those operators. I know it's not the same and this does indeed seem like very useful functionality. I would normally recommend requesting this feature on Right-Click Select, but with Geometry Nodes Tools coming to Blender 4.0 this is now irrelevant, because it will be possible to make tools like this(and a lot more) easily.

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  • $\begingroup$ Thanks, it seems you are correct, but sadly I would not prefer to have to make a tool like this using geonodes, when it would be a lot easier to simply choose 'deselect' when using Select Similar. Perhaps I will make a suggestion on Right-Click Select down the road ;) $\endgroup$ Oct 18, 2023 at 16:58
  • $\begingroup$ Great news about Node Tools in 4.0, but it might be bad news in this case. Devs might be less motivated to work on this when it is going to become somewhat irrelevant with new release anyway... Even if someone starts working on it now, they are not adding new features to 4.0 it would have to be 4.1 even in the absolute best scenario. I think you have better chances of asking for help with nodes here(when 4.0 comes out only - questions about development versions are not really best thing on BSE) or on Blenderartists.org/devtalk forums maybe. More selection tools would be great for many people. $\endgroup$ Oct 18, 2023 at 19:27

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