[Insight-developers] XML

[Yarden Livnat]

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Here is the first of the more specific email:

please remember that the other issues are
       1. XML description of ITK filters.
       2. Dynamic Compilation.
       3. Non-templated base classes for templated classes.

Background,
    SCIRun is similar in many respect to AVS, Data Explorer and the such.
The key difference between ITK and these system is that the pipeline is
constructed dynamically at run-time rather then at compile time as is 
done
with ITK. Each module (a more general version of an ITK filter) accept 
user
input (via a GUI) as well as input from other modules.

1. XML
     In order for us to create SCIRun modules from ITK filters without 
changing
     ITK code or imposing on ITK, we are using XML files that describe 
ITK filter.
     I attach an example of such an XML description files.  We are using 
these
     files to automatically generate SCIRun wrappers for each filter. 
Note that
     the same can be done for other system as well. This has a generic 
description.

     I understand that there is some effort (or at least a desire for 
some effort :-)
     to generate description files for ITK filters (and other ?). As 
such, we would like
     to coordinate this effort.

   Our view is to use a 3-level XML description.
      Level 1:
             ITK level XML: a single file per ITK filter which describe 
the fiter
             a.  templated:
                        Specify the template types of this filter. In 
other words, declare them
                        as new datatypes for the rest of the file, 
without specifying exactly what
                        they are
             b.  inputs/outputs: set/get which are part of the pipeline
             c.  parameters: things the users can set via the GUI. Note, 
each parameter
                        has only a name and a datatype (possibly a 
default value). It does *not*
                        specify how the user see or manipulate it (i.e., 
a double. The user may
                        interact with it via a text entry, a slider, 
etc.... but this is to specify some place
                        else as ITK itself does not deal with GUI).
            d.  include file: the *.h file which declare the filter.

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<filter-itk name="DiscreteGaussianImageFilter">
  <description>
  Blurs an image by separable convolution with 
  discrete gaussian kernels. This filter performs 
  Gaussian blurring by separable convolution of an 
  image and a discrete Gaussian operator (kernel).
  </description>
  <templated>
    <base>itk::Object</base>
    <template>InputImageType</template>
    <template>OutputImageType</template>
  </templated>

  <inputs>
    <input>
      <value>InputImageType</value>
      <num>1</num>
    </input>  
  </inputs>
  <outputs>
    <output>
      <value>OutputImageType</value>
      <num>1</num>
    </output>
  </outputs>

  <parameters>
    <param>
      <name>Variance</name>
      <type>double</type>
    </param>
    <param>
      <name>MaximumError</name>
      <type>double</type>
    </param>
  </parameters>
  <includes>
    <include>itkDiscreteGaussianImageFilter.h</include>
  </includes>
</filter-itk>


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      Level 2:
         GUI XML. Each such file specify for a given ITK filer how the 
parameters should be
          presented to the user. This is an application specific. There 
can be several GUI XML
          files for the same ITK filter each presenting the user with a 
different look. Obviously,
          only one GUI at a time can be used.

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<filter-gui name="Yarden-DiscreteGaussianImageFilterGui">
  <parameters>
    <param name="Variance">
      <gui>text-entry</gui>
      <default>10</default>
    </param>
    <param name="MaximumError">
      <gui>text-entry</gui>
      <default>0.001</default>
    </param>
  </parameters>
  <types>
    <type name="double">
      <guivar>GuiDouble</guivar>
    </type>
  </types>
</filter-gui>

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      Level 3:
           Application specifc. Which GUI XML to use with an ITK XML. 
Other application
           specific info.


XSLT:
     For SCIRun we wrote a few XSLT files which can take any ITK-XML 
files and generate
     the appropriate *.cc and *.h files. These files can then be 
compiled and linked into SCIRun
     without any modifications.

     The same can be done for other system/application. ie., a set of 
3-4 XSLT files which can
     translate each ITK XML files to the particular system. VTK is an 
example of a system which
     is hardcoded into ITK and which could (I think) have been connected 
via this kind of XML and
     XSLT files instead of Macros inside the C++ code. FLTK is an 
example of a GUI which can be
     connected to ITK via the same mechanism.

Are other people working on similar ideas ? Are there other things that 
should be put
into these XML files ?

One important point. We are _not_ going to implement this for each and 
every filter.
My view is that this should become a requirement for all ITK filters 
writers.

	Yarden


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