Function prepare_tiled_picture_surface 

fn prepare_tiled_picture_surface(
    surface_index: SurfaceIndex,
    slice_id: SliceId,
    surface_spatial_node_index: SpatialNodeIndex,
    map_pic_to_world: &SpaceMapper<PicturePixel, WorldPixel>,
    frame_context: &FrameBuildingContext<'_>,
    frame_state: &mut FrameBuildingState<'_>,
    tile_caches: &mut FastHashMap<SliceId, Box<TileCacheInstance>>,
)

Update dirty rects, ensure that tiles have backing surfaces and build the tile render tasks.