Function azul_core::app_resources::garbage_collect_fonts_and_images

pub fn garbage_collect_fonts_and_images<U: FontImageApi>(
    app_resources: &mut AppResources, 
    render_api: &mut U, 
    pipeline_id: &PipelineId
)

To be called at the end of a frame (after the UI has rendered): Deletes all FontKeys and FontImageKeys that weren't used in the last frame, to save on memory. If the font needs to be recreated, it needs to be reloaded from the FontSource.