ludum_dare_46/res/shaders/s2e/frag.gls

#version 330 core

uniform sampler2D sampler;
uniform vec3 iColor;
uniform float time;

in vec2 texCoords;

out vec4 color;

void main() {
    vec4 sample = texture(sampler, texCoords);
    float x = sample.r + time;
    color = vec4(iColor, mod(floor(x), 2) * (-x + 2) * sample.a);
	if (color.a == 0) {
	    discard;
	}
}