Barrel Distortion

https://gyazo.com/ccd6a3b0f3c6c03b67a3e19d231100c7

GLSL

code:glsl

vec2 barrel(vec2 uv, float k) {

float aspect = resolution.x / resolution.y;

vec2 p = uv * 2.0 - 1.0;

p.x *= aspect;

p *= 1.0 + k * dot(p, p);

p /= 1.0 + k * (aspect * aspect + 1.0);

p.x /= aspect;

return p * 0.5 + 0.5;

}