Function render_slide_drawn 

pub fn render_slide_drawn(
    pres: &Presentation,
    index: usize,
    opts: &RenderOpts<'_>,
) -> (Image, Rect)

render_slide, also returning how far the drawing reached, in slide space (at least the slide; off it, what the shapes, their effects and their text drew, the parts outside the output included). The editor grows its pasteboard to it (pasteboard_region).