Frag shader: circle follows mouse

circle_mouse_frag_shader.txt

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec3 col = vec3(0.5, 0.5, 0.5);
    float radius = 50.0;
    float dist_squared = dot(iMouse.xy - fragCoord.xy, iMouse.xy - fragCoord.xy);
    if (dist_squared < (radius * radius)) {
    	col += vec3(0.0, 1.0, 1.0);
    }
    fragColor = vec4(col,1.0);
}