[Paraview-developers] Changing ColorMaps.xml format

[Utkarsh Ayachit]

Folks,

I am looking at adding tracing support for loading color map presets.
When doing that,
I am also looking at extending the "presets" mechanism to support
saving/loading opacity transfer function (along with color) and other
things that may be important in preset.

As I am doing this, I realize that the ColorMaps XML format is very
limited, for example, there's no way to save the BelowRangeColor in a
preset. If we go on extending the XML to add support for other
attributes on the color/opacity map that a user may potentially want
to save in a color map, we would just end up with a different way to
specifying what the XML state for the PVLookupTable proxy saves
anyways. If I remember correctly, we invented the ColorMap XML format
since we thought the lookuptable proxy's XML state will be too complex
for a user to manually create.

So here's a proposal: why don't we change the color map file format to
be a JSON  instead, that matches what we currently save in
UserSettings.json file anyways. e.g.

       {
         "Annotations" : [ "100", "100" ],
         "BelowRangeColor" : [ 0.6666666666666666, 0, 0 ],
         "ColorSpace" : "HSV",
         "NanColor" : [ 1, 1, 0 ],
         "RGBPoints" : [
            37.35310363769531, 0.278431, 0.278431, 0.858824,
            71.59813206481934, 0, 0, 0.360784,
            105.6036847686768, 0, 1, 1,
            140.0881889190674, 0, 0.501961, 0,
            174.0937416229248, 1, 1, 0,
            208.3387700500488, 1, 0.380392, 0,
            242.5837984771728, 0.419608, 0, 0,
            276.8288269042969, 0.878431, 0.301961, 0.301961
         ],
         "UseBelowRangeColor" : 1
      }

All fields are of course optional. Thus for the attributes supported
by the current color map xml, the JSON would only be something like:

       {
         "ColorSpace" : "HSV",
         "NanColor" : [ 1, 1, 0 ],
         "RGBPoints" : [
            37.35310363769531, 0.278431, 0.278431, 0.858824,
            71.59813206481934, 0, 0, 0.360784,
            105.6036847686768, 0, 1, 1,
            140.0881889190674, 0, 0.501961, 0,
            174.0937416229248, 1, 1, 0,
            208.3387700500488, 1, 0.380392, 0,
            242.5837984771728, 0.419608, 0, 0,
            276.8288269042969, 0.878431, 0.301961, 0.301961
         ]
      }

This is not much more complex the current color map XML, for example:

  <ColorMap name="Rainbow Desaturated" space="HSV">
    <Point x="0.0" r="0.278431372549" g="0.278431372549"
b="0.858823529412" o="0.0"/>
    <Point x="0.143" r="0.0" g="0.0" b="0.360784313725" o="0.143"/>
    <Point x="0.285" r="0.0" g="1.0" b="1.0" o="0.285"/>
    <Point x="0.429" r="0.0" g="0.501960784314" b="0.0" o="0.429"/>
    <Point x="0.571" r="1.0" g="1.0" b="0.0" o="0.571"/>
    <Point x="0.714" r="1.0" g="0.380392156863" b="0.0" o="0.714"/>
    <Point x="0.857" r="0.419607843137" g="0.0" b="0.0" o="0.857"/>
    <Point x="1.0" r="0.878431372549" g="0.301960784314"
b="0.301960784314" o="1.0"/>
    <NaN r="1.0" g="1.0" b="0.0"/>
  </ColorMap>

Of course, we'll support loading old style XMLs for backwards
compatibiltiy as well as a tool to convert old style XMLs to the new
style json.

Thoughts? Objections? Alternative suggestions?

Utkarsh