[Paraview-developers] Color Scale Editor Design

[Utkarsh Ayachit]

What are you doing to add support for Gradient Opacity Transfer
function? It's just a new LookupTable and/or PiecewiseFunction proxy?
The new color editor is not going to be a special panel but simply a
generic "pqProxyWidget" that autogenerates widgets for all properties
on the proxy (with custom widgets for properties as needed). It should
be able to show a different proxy (with more/custom widgets) without
much of an issue.

Utkarsh

On Thu, Jul 11, 2013 at 6:23 AM, Biddiscombe, John A. <biddisco at cscs.ch> wrote:
> One of the features I have an intern working on - and I need, is the ability to use Gradient Opacity for volume rendering. I had a plugin which enabled this, using a 2D transfer function editor (stolen from visit again, like the point sprite stuff, but I ended up having to rewrite most of it)
>
> Could you please make it easy for me to hook this kind of feature into the standard colour editor? rather than having to redo it all in the plugin.
>
> None of it compiles at all right now as it was last used in 2010 and the server manager and everything has been completely changed. I asked about this on the list a week or so ago, but now I see from looking at the code that the vol-render plugin I made is obsolete as the one in paraview does camera aligned slices etc, All I need to do is expose the gradient opacity features and hook my editor into them. (It does histograms and stuff too inside the editor, but probably there's a vtk2DTransferFunction Widget somewhere we could use instead).
>
> Etc etc, just thinking out loud.
>
> JB
>
>> -----Original Message-----
>> From: paraview-developers-bounces at paraview.org [mailto:paraview-
>> developers-bounces at paraview.org] On Behalf Of Utkarsh Ayachit
>> Sent: 10 July 2013 20:24
>> To: burlen
>> Cc: ParaView Developers
>> Subject: Re: [Paraview-developers] Color Scale Editor Design
>>
>> Burlen,
>>
>> > 1) combine the opacity widget and the color scale widget.
>>
>> Good idea! Let me see how much effort that's going to be. Hopefully, it's not
>> too bad to add support for this.
>>
>> > I think it would also be very useful to display a histogram of the active scalar
>> plotted using the LUT colors in the new widget.
>>
>> We have thought of this in the past. As useful that this is, it's a bit tedious to
>> implement. I'll put that as a feature request to be addressed in future for
>> now.
>>
>> > 2) add a "mirror scale" option.
>>
>> Should be too hard to add.
>>
>>
>> > Also, with the current color scale widget it's pretty difficult to interactively
>> manipulate LUT's with many color points (eg when 256 colors are explicitly
>> specified). The control points are too close together to select and they way
>> it's implemented now you'd need to move surrounding control points as
>> well.
>>
>> Burlen, for such cases you may want to look into using the newly added
>> "categorical color" support rather than adding 256 control points.
>>
>>
>> > 3) limit the number of control points used by the widget. The default max
>> number of control points used by the widget would be something
>> reasonable like 16 but the user could increase if desired via a qt spin control.
>> The active control points in the widget would be evenly spaced across the
>> scale and during interaction as the user moves the visible control points the
>> widget would handle linearly re-interpolating the position of the hidden
>> control points automatically.
>>
>> I'm not sure I follow the need for this. With support for categorical colors,
>> some of the use-cases with large number of control points may become
>> unnecessary.
>>
>> Utkarsh
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