[Bf-funboard] Selection keys and UV maps

[Campbell Barton]

On Fri, Aug 3, 2012 at 5:49 PM, Ruth Ivimey-Cook <ruth at ivimey.org> wrote:
> Hi Campbell
>
> Thanks for having a go.
>
>> Will try to answer you're questions inline...
> :-)
>>
>> Ruth Ivimey-Cook<ruth at ivimey.org>  wrote:
>>> 2. The models I am making right now are almost exclusively of things
>>> with flat and mostly rectangular faces. When trying to make UV maps of
>>> these, the existing tools far too often either distort the aspect ratio
>>> of the original face, or utterly distort it out of recognition. As
>>> normally the texture is coming from real life (eg a wall), neither
>>> action is acceptable as the resultant distortion or scaling will be
>>> quite obvious, so I have to go round individually tweaking things:
>>> extremely laborious.
>> Blender has quite a few tools to handle these cases
>> - Select a face, Shift+G, Co-planer OR Normals, Then Ukey - project from view.
>>
>> - UV project modifier (nice if you want to edit without distoring UVs)
>>
>> - Ukey - smart uv unwrap
>>
>> - Ukey - follow active quads (relies on a grid topology)
> Yes, I've been (trying to) use these tools, but for the models I am
> making (buildings, i.e. complex box shapes) they generally end up with
> one of the following:
>
>   - faces all over the map, with no continuity of placement, making the
> subsequent texturing hard or impossible. This is typically true of
> "Smart UV", which in my experience is a misnomer.
>
>   - faces in groups/islands, but distorted into all sorts of shapes
> because of the 3D->2D mapping. Can be resolved with appropriate seam
> lines, but still very hard indeed to retain the proportions of the
> original faces, which is for me vital.

Smart UV simply groups faces by their normals, then projection maps
them - box packing the islands after.

It should only ever distort is you have gradually curved surfaces or 2
faces at a few degrees different.
Perhaps just using a lower angle will fix this? 5-15deg.

>   - Faces overlaid on each other in a complete mess - typical of the
> Cube method - can work, but it's almost impossible to work out which
> face is where, especially when (as I do) you have multiple small faces
> (think of a set of window surrounds on a multi-window building). Most
> faces don't get into big enough islands to help identify.

Normally when modeling buildings I split up geometry so windows
wouldnt be in some mesh as other parts of a building, also often you
can instance the window frames so you only need to UV map once.

> Perhaps I'm guilty of being dumb or ignorant in that I just don't know
> how to do it "the right way" - but then I haven't discovered the right
> way, and I have looked. The manual typically says what the controls do,
> but doesn't explain how to use them effectively or how to use groups of
> actions to achieve a goal.

Alas - blenders manual isn't up to scratch - but I wouldn't worry
about finding this stuff tricky, it might be best if you just post the
model, and some UV's you would expect to be simple to map. - If an
experienced user can't redo this easily it points to the tools
lacking. -- This stuff is hard to explain as text I find.

>>
>>> - I would like a UV mapping "mode" which above all else faithfully
>>> preserves the shape of every face (perhaps unless the operator
>>> explicitly moves UV vertices or edges). I realize this may mean it's
>>> impossible to map, so how about the following:
>>>
>>> - Modifying the view of the UV map window to actually be 3D? If a face
>>> can't map to the UV plane, it's extended out in the "W" direction and
>>> the operator can see it using the standard 3d movement tools used in the
>>> 3D window.
>> I don't really know what you mean here, it sounds like some quite
>> large changes - but would need a much more detailed description to
>> comment. Also, Id be interested to know the use case. - Why existing
>> tools fail.
> The change would be to make the UV window a UVW window, i.e. 3D, in
> exactly the same style as the current 3D window in wireframe or solid
> mode. The window would use the 3rd dimension to render the
> faces/vertices that currently aren't flat on UV.
>
> You can then see at a glance when you have an issue to resolve and take
> appropriate action.
>
> If you don't resolve things, the map exported and used outside the UV
> window is the face-on UV map, i.e. the same projection that you get if
> you look in the 3D window using the "Top Ortho" view.

Did you use this feature in some other application? - I only ever
seriously did UV mapping in blender.

>>> While in some ways this puts the onus back on the user to sort out the
>>> seams etc, it seems to me this would make it a lot easier to identify
>>> the problem areas.
>> Again, I dont really follow you exactly - there is a view option to
>> see UV distortion (where red is highly distorted and blue isnt).
> One of my goals is to achieve a UV map in which there is no distortion
> of any edge, because the map never had any, rather than you found all
> the "red"s and eliminated them.
>
> BTW Blue <-> Red is a really bad choice of colour shade: Blue is one of
> the hardest colours to see and shades of blue are not very distinguishable.

Eeeh, these colors are used for weightpaint too so its at least
consistent, with weight painting its possible to define custom colors,
but not UV stretching. Personally I never found this an issue though
UV weights could have their own colorbands too.

>> Being able to edit multiple UV's at once would be really nice.
> Can it be put on the "todo" list at some point. I see many people on
> lists asking how to do it and being disappointed. It seems (unlike my
> earlier suggestion) that it ought to be relatively simple, if you go
> with the "you can only edit one object at once" rule.

To do this in a general way we need to be able to enter editmode for
multiple objects at once, this is a fairly big undertaking, so not
sure listing as a TODO really helps, its more a good feature to have
and devs are aware of it.

>> As a workaround for not having this there are a few options. - Temp
>> join many objects into one, unwrap - then copy UV's back to the
>> original objects, requires some scripts but works ok. - There is an
>> option in the image space "View -> Draw Other Objects". Regards
> Where can I find out more about doing this?

Sergey Sharybin wrote a script to do this but its not released, such
tools are fairly trivial to write but needs to be made into an addon
or so - I'll check on this.

-- 
- Campbell