void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    vec2 uv = fragCoord / iResolution.xy;
    uv = vec2(uv.x, 1.0 - uv.y);
    // mixes two textures
    //fragColor = mix(texture(iChannel0, uv), texture(iChannel1, uv), 0.2);

    vec2 tex_uv = vec2(fragCoord.x, 1.0 - fragCoord.y);
    // test resolutions
    //fragColor = texture(iChannel0, tex_uv / iChannelResolution[0].xy);

    // combine them!
    fragColor = mix(texture(iChannel0, tex_uv / iChannelResolution[0].xy), texture(iChannel1, tex_uv / iChannelResolution[1].xy), 0.2);
}