Играюсь с Webgl и читаю книгу https://thebookofshaders.com

mouse_coords.glsl

#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

void main() {
    vec2 st = gl_FragCoord.xy/u_resolution;
    vec2 mt = u_mouse/u_resolution;
    float yd = abs(mt.y - st.y);
    float xd = abs(mt.x - st.x);
    float t = 0.0;
    if (yd < 0.002 || xd < 0.002){
        t = 1.0;
    }
    gl_FragColor = vec4(sin(u_time / 3.),sin(u_time / 5.),sin(u_time / 4.), t);
}