dynamic stretching filter for mpv, aiming to bring effects similar to GoPro SuperView. use along with '--no-keepaspect'

hyperview.hook

//!DESC hyperview
//!HOOK MAIN
//!WHEN OUTPUT.width OUTPUT.height / MAIN.width MAIN.height / / 0.667 >
//!WIDTH OUTPUT.width
//!BIND HOOKED

vec4 hook() {
    float r = (target_size.x / target_size.y) / (HOOKED_size.x / HOOKED_size.y);

    // y = (r - 1) * x^3 + x

    float y = (HOOKED_pos.x - 0.5) * 2.0 * r;
    float x = y / r;
    x -= ((r - 1.0) * x * x * x + x - y) / (3 * (r - 1.0) * x * x + 1.0);
    x -= ((r - 1.0) * x * x * x + x - y) / (3 * (r - 1.0) * x * x + 1.0);
    x -= ((r - 1.0) * x * x * x + x - y) / (3 * (r - 1.0) * x * x + 1.0);
    x -= ((r - 1.0) * x * x * x + x - y) / (3 * (r - 1.0) * x * x + 1.0);
    x -= ((r - 1.0) * x * x * x + x - y) / (3 * (r - 1.0) * x * x + 1.0);
    return HOOKED_tex(vec2(x / 2.0 + 0.5, HOOKED_pos.y));
}