Request: Allow Gravatar's "d" param to be filtered

[henry.wright]

Inside bp_core_fetch_avatar(), the d param is set like this:

if ( 'gravatar_default' !== $default_grav ) {
    $url_args['d'] = $default_grav;
}

$default_grav will be either wavatar, mm etc. These are the "default" default images (generated by Grav). But Gravatar also allows d to be a URL:

Ref: ​https://en.gravatar.com/site/implement/images/#default-image

Is it possible to add a filter which lets us change the value of the d param before it's passed to Gravatar?

I'm thinking $params would be useful to have in hooked functions because from that we could get the user or group ID etc.

[henry.wright]

Looking at WordPress, the default arg can be set using a filter such as pre_get_avatar_data. The problem is, the value doesn't carry through into bp_core_fetch_avatar().

[henry.wright]

6989.diff introduces a bp_core_avatar_default filter hook which allows Gravatar's "d" param to be filtered.

[dcavins]

In 10688:

bp_core_fetch_avatar(): Add "d" filter.

Add a filter for the Gravatar “d,” or
“default_gravatar” parameter.

Props henry.wright.

Fixes #6989.