Function draw_layer_perspective

fn draw_layer_perspective(
    dst: &mut Frame,
    src: &Frame,
    p: Placement,
    mode: BlendMode,
    opacity: f32,
    scaler: Scaler,
    scratch: &mut Frame,
    mask: Option<&[u8]>,
)

Perspective path: project the placed rect’s corners tilted by yaw (about Y) and pitch (about X) with focal length = canvas width, then inverse-map each canvas pixel through the homography.