Function draw_filled_rect_mut 

pub fn draw_filled_rect_mut<C>(canvas: &mut C, rect: Rect, color: C::Pixel)
where
    C: Canvas,

An in-place version of draw_filled_rect().

This function does the same operation as draw_filled_rect() but on the &mut image passed rather than cloning an &image. This is faster but you lose the original image.