#define OR(A,B) (A+B-A*B)
#define AND(A,B) ((A)*(B))
#define NOT1(A) (1.-A)
#define NOT(A,B) AND(A,NOT1(B))

#define XOR(A,B) AND(OR(A,B),NOT1(AND(A,B)))

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

    uv.x += 0.1;
    vec3 A = step(length(uv*2.-1.),0.2) * vec3(1.,0.,0.);
    uv.x -= 0.1;
    vec3 B = step(length(uv*2.-1.),0.2) * vec3(1.,1.,0.);

    fragColor = vec4(XOR(A,B),1.0);
}

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

    uv.x += 0.1;
    vec3 A = step(length(uv*2.-1.),0.2) * vec3(1.,0.,0.);
    uv.x -= 0.1;
    vec3 B = step(length(uv*2.-1.),0.2) * vec3(1.,1.,0.);

    fragColor = vec4(abs(A-B),1.0);
}

multiply   a * b
screen   1 - (1 - a) * (1 - b)
darken   min(a, b)
lighten   max(a, b)
difference   abs(a - b)
negation   1 - abs(1 - a - b)
exclusion   a + b - 2 * a * b
overlay   a < .5 ? (2 * a * b) : (1 - 2 * (1 - a) * (1 - b))
hard light   b < .5 ? (2 * a * b) : (1 - 2 * (1 - a) * (1 - b))
soft light   b < .5 ? (2 * a * b + a * a * (1 - 2 * b)) : (sqrt(a) * (2 * b - 1) + (2 * a) * (1 - b))
dodge   a / (1 - b)
burn   1 - (1 - a) / b