Default file rules behaviour is counter intuitive and possibly broken.

[KelSolaar]

Hi,

As I started to poke at OCIO 2 for the new ACES config, I wanted to test the new ExponentWithLinearTransform transform.

Upon validation I get the well deserved:

CRITICAL:root:Only config version 2 (or higher) can have ExponentWithLinearTransform.

All good, I set my major version to 2:

config.setMajorVersion(2)

After which:

CRITICAL:root:Config failed validation. File rules failed with: File rules: rule named 'Default' is referencing color space 'default' that does not exist.

Which can be fixed by creating a new default ColorSpace but then because I don't like the default name and I remember #893 and specifically:

file_rules:
    !<Rule> {name: LogC, extension="*", pattern="*LogC*", colorspace=ARRI LogC}
    !<Rule> {name: OpenEXR, extension="[eE][xX][rR]", pattern="*", colorspace=ACEScg}
    !<Rule> {name: TIFF, regex=".*\.TIF?F$", colorspace=sRGB}
    !<Rule> {name: ColorSpaceNamePathSearch}
    !<Rule> {name: Default, colorspace=Raw}

I decided to add my own which raised the following exception:

Traceback (most recent call last):
  File "/Users/kelsolaar/Documents/Development/colour-science/ampas/OpenColorIO-Config-ACES/opencolorio_config_aces/config/generate/config.py", line 297, in <module>
    generate_config(data, 'config.ocio')
  File "/Users/kelsolaar/Documents/Development/colour-science/ampas/OpenColorIO-Config-ACES/opencolorio_config_aces/config/generate/config.py", line 236, in generate_config
    file_rules.insertRule(
PyOpenColorIO.Exception: File rules: A rule named 'Default' already exists.

[doug-walker]

Hi Thomas,

The FileRules object always has a Default rule, so you cannot use insertRule in that case. In other words, the Default rule cannot be added or removed. There is a method called setDefaultRuleColorSpace that does what you are looking for.

As discussed elsewhere, I agree it would be helpful to have an example to illustrate the usage.

[KelSolaar]

It makes things a bit more convoluted than one would wish but this works!

Given this data:

        file_rules=[
            {
                'name': 'Default',
                'colorspace': 'Gamut - sRGB'
            },
            {
                'name': 'Linear - sRGB',
                'colorspace': 'Gamut - sRGB',
                'regex': '_[sS][rR][gG][bB]\\.([eE][xX][rR]|[hH][dD][rR])$'
            },
            {
                'name': 'EOTF - sRGB',
                'colorspace': 'CCTF - sRGB',
                'regex': '_[sS][rR][gG][bB]\\.([pP][nN][gG]|[tT][iI][fF])$'
            },
        ],

Here is what I came up with:

    file_rules = ocio.FileRules()
    rule_index = 0
    for file_rule in data.file_rules[::-1]:
        name = file_rule['name']
        colorspace = file_rule['colorspace']
        regex = file_rule.get('regex', '')
        pattern = file_rule.get('pattern', '')
        extension = file_rule.get('extension', '')
        if name == 'Default':
            file_rules.setDefaultRuleColorSpace(colorspace)
        elif regex:
            file_rules.insertRule(rule_index, name, colorspace, regex)
            rule_index += 1
        else:
            file_rules.insertRule(rule_index, name, colorspace, pattern,
                                  extension)
            rule_index += 1
    config.setFileRules(file_rules)