In the past (and in the HDK samples), .icon files are used but we recommend that you use SVG files for new operators. SVG (and .icon) files are resolution independent and so they work best for operators displayed in the network view pane. There are several tools available on all platforms for creating SVG files such as Inkscape.
The icon filename corresponds to the table and name of the new operator. Then, by default, Houdini will use that icon for the operator. For example, if we have a new object operator named
hdk_lamp, then the corresponding icon will be
OBJ_hdk_lamp.svg. If you are unsure about the name, missing operator icons will have their name printed out to the shell when Houdini starts up.
When the icon is complete (to your satisfaction), it should be installed somewhere in the HOUDINI_UI_ICON_PATH search path. This is typically at
but on Mac it can be
where X.Y is the Houdini major and minor version numbers respectively.