Function render_cursor 

pub fn render_cursor(
    pixels: &mut [u8],
    width: u32,
    height: u32,
    cursor: &CursorImage,
    mouse_pos: (i16, i16),
)

Overlay the cursor onto an RGBA pixel buffer.

cursor is (bitmap, mask, hotspot_v, hotspot_h) — 16x16 1-bit cursor. mouse_pos is (v, h) in Mac screen coordinates.