#extension GL_OES_standard_derivatives : enable

precision mediump float;

in vec2 uv;
in vec4 type_color;
out vec4 color;

void main(){
    float x = (uv.x - 0.5) * 2.0;
    float y = (uv.y - 0.5) * 2.0;
    float r_squared = x * x + y * y;
    float alpha = 1.0;

#ifdef GL_OES_standard_derivatives
    float delta = fwidth(r_squared);
    alpha = 1.0 - smoothstep(1.0 - delta, 1.0 + delta, r_squared);
    color = vec4(type_color.rgb, alpha);
#else
    if (r_squared <= 1.0){
        color = type_color;
    }
    else{
        color = vec4(0.0, 0.0, 0.0, 0.0);
    }
#endif
}