Shadertoy: Wobble

shader5.fsh

// https://www.shadertoy.com/view/XtsGDj
void main() {
    vec4 val = texture2D(u_texture, v_tex_coord);
    vec4 grad = texture2D(u_gradient, v_tex_coord);
    
    if (val.a < 0.1 && grad.r < 0.65 && grad.a > 0.8) {
        float t = u_time;
        vec2 uv = (gl_FragCoord.xy / u_sprite_size.xy)*2.0-1.0;
        float angle = atan(uv.y,uv.x) + t;
        float k = true ? sin(t)*2.0 : 1.0;
        angle -= length(uv) * k;
        
        vec3 gold = vec3(.0, 0.94, 0.0);
        gl_FragColor = vec4(gold*vec3(cos(8.*angle)),1.0);
    } else {
        gl_FragColor = val;
    }
}