Constant TINT

const TINT: &str = r#"
void main() {
    vec2 uv = gl_FragCoord.xy / u_res;
    vec4 src = texture(tex, uv);
    vec4 res = vec4(mix(src.rgb, vec3(p0, p1, p2) / 255.0, clamp(p3, 0.0, 1.0)), src.a);
    float m = u_has_mask > 0.5 ? texture(u_mask, uv).r : 1.0;
    out_color = mix(src, res, m);
}
"#;

Mix towards (p0,p1,p2) 0..255 by p3.