simple 2D shader

test.glsl

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 center = iResolution.xy / 2.0;
    float r1 = iResolution.y / 5.0;
    float r2 = iResolution.y / 3.0;
    
	vec2 uv = fragCoord.xy / iResolution.xy;
    float dist = distance(fragCoord.xy, center);
    if( dist >= r1 && dist <= r2) {
        float d = (dist-r1)/(r2-r1);
        fragColor = vec4(d, 1.0-d, 0.5+0.5*sin(iGlobalTime), 1);
    }
    else
		fragColor = vec4(uv,0.5+0.5*cos(iGlobalTime),1.0);
}