out vec4 FragColor;
in vec2 aUv;
uniform float uT;

void main(){
   float d = uT + distance( aUv, vec2(0.5,0.5) );

   vec3 vDither = vec3( dot( vec2( 171.0, 231.0 ), gl_FragCoord.xy) );
   float dither = fract( vDither.g / 71.0 ) - 0.5;

   if( d+dither < -0.5 )
      discard;

   FragColor = vec4( 1.0, 0.0, 0.0, 1.0 );
}