// adapted from https://www.shadertoy.com/view/Xd3BWr

uniform vec2 uSize;
uniform float iTime;
vec2 iResolution;
out vec4 fragColor;

void main(void) {

    iResolution = uSize;
    vec2 fragCoord = gl_FragCoord.xy; // Get the fragment coordinates

    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = fragCoord/iResolution.xy;

    float c = uv.x * 2.0 + iTime*2.0;
    c = mod(c, 1.0);
    c = step(c, 0.5);
    fragColor = vec4(0.0, 0.0, 0.0, c);
}