...

• The type of node using the texture: pattern, light, lightfilter or imageplane.
• A set of base parameters for that type of node
• one or more rules to modify the base parameters when considering the file's name, the bit depth, etc.

These Custom settings are defined in a $RMANTREE/etc/txmanager_rules.json.can be defined by the ocio configuration. 

JSON structure

Here is a very basic example. See  $RMANTREE/etc/txmanager_rules.json for the real rules.

{
    "pattern": {
        "args": {
            "texture_type": "regular",
            "smode": "periodic",
            "tmode": "periodic",
            "texture_format": "pixar",
            "texture_filter": "catmull-rom",
            "resize": "up-",
            "data_type": null,
            "compression": "lossless",
            "compression_level": null
        },
        "rules": {
            "'_i8t' in '%(img_name)s'": {
                "args": {
                    "texture_format": "tiff",
                    "data_type": "byte"
                }
            }
		}
	}
}

Category

In the example above, the category is pattern , but there are other pre-defined categories: light , lightfilter and  imageplane.

args

This section is a dictionary representing default txmake parameter values for the current category. The key names ( texture_type, smode, tmode , etc) are coming from the TxParams class of the txmanager python module.

rules

Here we define a set of rules that will all be executed in the file's order. The key string should evaluate as a python expression and return True once substituted.

There are a number of available substitution tokens:

...

In the example above, the rule:

"'_i8t' in '%(img_name)s'": {
	"args": {
		"texture_format": "tiff",
		"data_type": "byte"
	}
}

... matches "_i8t" in the image name, which is here interpreted as shorthand for "8 bits integer tiff format" and sets the texture format to "tiff" and the image to "byte" (8 bits integer, see txmake documentation). For example, a file named "roof_top_diffColor_i8t_v06.png" would match that rule.

Of course, you can create more sophisticated tests by using the and and or keywords.

"'%(img_type)s' == 'float' and %(img_depth)d > 16"

...