Function prepare_composite_mode 

pub fn prepare_composite_mode(
    composite_mode: &PictureCompositeMode,
    surface_index: SurfaceIndex,
    parent_surface_index: SurfaceIndex,
    surface_rects: &SurfaceAllocInfo,
    snapshot: &Option<SnapshotInfo>,
    can_use_shared_surface: bool,
    frame_context: &FrameBuildingContext<'_>,
    frame_state: &mut FrameBuildingState<'_>,
    data_stores: &mut DataStores,
    extra_gpu_data: &mut SmallVec<[GpuBufferAddress; 1]>,
) -> (SurfaceDescriptor, [Option<RenderTaskId>; 2])