Function overlay_cursor 

pub(crate) fn overlay_cursor(
    frame: &mut [u8],
    stride: usize,
    frame_w: i32,
    frame_h: i32,
    cur_w: i32,
    cur_h: i32,
    pixels: &[u32],
    img_x: i32,
    img_y: i32,
)

Composite the XFixes cursor (ARGB u32 per pixel, premultiplied by the XFixes format definition) onto the BGRA frame with its top-left at (img_x, img_y), blending each pixel through blend_pixel_premultiplied with per-pixel bounds clipping so an image straddling a frame edge writes only its in-frame portion.