#version 300 es
precision highp float;

in vec2 v_texcoord;
uniform sampler2D tex;
out vec4 fragColor;

float rand(vec2 co) {
    return fract(sin(dot(co, vec2(12.9898, 78.233))) * 43758.5453);
}

void main() {
    vec4 c = texture(tex, v_texcoord);

    float grain = rand(v_texcoord) * 0.08 - 0.04;
    c.rgb += grain;

    fragColor = clamp(c, 0.0, 1.0);
}