dame.txt

float s = 0.01;
float stroke = 0.02;

float circulo(in vec2 c, in float r, in vec2 uv){
    
    float d = distance(c, uv);
    return 1.0-smoothstep(r-s,r+s,d);
}

float circunferencia(in vec2 c, in float r, in vec2 uv){
   return circulo(c,r,uv) - circulo(c,r-stroke,uv);

}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uvt = fragCoord/iResolution.xy;
    vec2 uv = (2.0*(fragCoord/iResolution.xy))-1.0;

    uv.x *= iResolution.x/iResolution.y;

    float raio = cos(iTime)/4.0+0.5;
    float cor = circunferencia(vec2(0.5,0.0), raio, uv) + circulo(vec2(-0.5,0.0), raio, uv);
    
    vec4 yellow = vec4(1.0,1.0,0.0,1.0);
    vec4 blue   = vec4(0.0,0.0,0.7,1.0);
    
    vec4 txtr = texture(iChannel0,uvt);
    vec4 dame = texture(iChannel1,uvt);
    
    //fragColor = cor*yellow+(1.0-cor)*blue, 1.0;
    fragColor = cor*txtr+(1.0-cor)*dame, 1.0;
}