kupa

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = fragCoord.xy / iResolution.xy;
    vec4 texColor = texture(iChannel0, uv);

    float m = (texColor.r + texColor.g + texColor.b)/3.0;
    fragColor.r = texColor.r - m*abs(sin(iGlobalTime));
    fragColor.g = texColor.g - m*abs(sin(iGlobalTime));
    fragColor.b = texColor.b - m*abs(sin(iGlobalTime));
    fragColor.a = texColor.a;
}