Possibility to use custom icons in buttons

[f1ames]

Are you reporting a feature request or a bug?

Feature request

Provide detailed reproduction steps (if any)

At the moment button icons can be defined only in two ways:

Automatically based on button/command name like:

editor.ui.addButton( 'Bold', {
    command: 'bold'
} );

The icons used this way must be registered earlier via CKEDITOR.skin.addIcon. Registration happens automatically when icons are defined via pluginDefinition.icons and this is the way it is used in all cases now:

https://github.com/ckeditor/ckeditor-dev/blob/9409e28dadf1564ec35987bcd888dfe6df23ef0d/plugins/basicstyles/plugin.js#L6-L10

This mechanism also assumes that icons are placed under the following path ckeditor_root_folder/plugins/plugin_name/icons/icon_name.png and ckeditor_root_folder/plugins/plugin_name/icons/hidpi/icon_name.png for HiDPI versions.

Reuse icons from other plugins

Button can be also defined like:

editor.ui.addButton( 'Button', {
    command: 'button_command',
    icon: 'name'
} );

And then it will reuse the icons defined (as described above) in other plugin with a given name.

Solution

For more flexibility we would like to add possibility to defined button icon only by passing path to icon image/file to button definition:

editorInstance.ui.addButton( 'MyBold', {
    command: 'bold',
    icon: 'icon_path.png',
    iconHidpi: 'hidpi_icon_path.png'
} );

For more detailed information how paths should be defined and how are resolved, you may refer to docs in the code (or CKEDITOR.ui.addButton SDK after 4.9.0 release):
https://github.com/ckeditor/ckeditor-dev/blob/9409e28dadf1564ec35987bcd888dfe6df23ef0d/plugins/button/plugin.js#L409-L435