e7.pix

#define NUMBER_TO_PRINT esol
#define DISTANCE_BETWEEN_DIGITS 0.05
#define LINE_WIDTH 0.05
#define ON_COLOR  vec4(0.0, 1.0, 0.0, 1.0);
#define OFF_COLOR vec4(0.0, 0.0, 0.0, 1.0);
float digits(float x) {
    if (x < 2.0) { return 1.0; }
    return ceil(log(x) / log(10.0));
}

int imod(int x, int y) {
    return x - y*(x/y);
}
int euler7() {
    int numprimes = 1;
    int ans = 0;
    for (int i = 3; i < 150000; i += 2) {
        bool isprime = (imod(i, 2) != 0);
        for (int j = 3; j*j <= i; j += 2) {
            isprime = isprime && (imod(i, j) > 0);
        }
        numprimes  = numprimes + int(isprime);
        ans       += (int(numprimes == 10001) * i);
        numprimes += int(numprimes == 10001);
    }
    return ans;
}

uniform vec3 iResolution;
void main(void)
{
    int esol = euler7();
    vec2 uv = gl_FragCoord.xy / iResolution.xy;
    //Below line switches between glsl and webgl coordinaes
    //uv.y = 1.0 - uv.y;
    float N = digits(float(NUMBER_TO_PRINT));
    float width = (1.0 - (N-1.0)*DISTANCE_BETWEEN_DIGITS) / N;
    float digit = floor(uv.x / (width + DISTANCE_BETWEEN_DIGITS));
    //coordinates within box
    float digitStartx = (width+DISTANCE_BETWEEN_DIGITS)*digit;
    float digitEndx   = digitStartx + width;
    vec2 sub_uv = vec2((uv.x - digitStartx) * 1.0/(digitEndx - digitStartx), (uv.y - .2) * (1.0/.6));
    
    //Computing a power of 10 was made harder because webgl
    //Could do something less silly in actual glsl
    int p = 1;
    for (int i = 0; i < 10; ++i) {
        p *= (1 + int(i < int(N) - int(digit)) * 9);
    }

    int currentDigit = imod(NUMBER_TO_PRINT, p) / (p/10);
    //Determining the position
    bool tiptop   = sub_uv.y < LINE_WIDTH && sub_uv.y > 0.0;
    bool top      = sub_uv.y < 0.5 - LINE_WIDTH/2.0&& sub_uv.y > 0.0;
    bool left     = sub_uv.x > 0.0                 && sub_uv.x < LINE_WIDTH;
    bool middle_x = sub_uv.x > LINE_WIDTH          && sub_uv.x < 1.0 - LINE_WIDTH;
    bool middle_y = sub_uv.y > 0.5 - LINE_WIDTH/2.0&& sub_uv.y < 0.5 + LINE_WIDTH/2.0;
    bool right    = sub_uv.x > (1.0 - LINE_WIDTH)  && sub_uv.x < 1.0;
    bool bottom   = sub_uv.y > 0.5 + LINE_WIDTH/2.0&& sub_uv.y < 1.0;
    bool botbot   = sub_uv.y > 1.0 - LINE_WIDTH    && sub_uv.y < 1.0;
    
    //shorthand
    int c = currentDigit;
    bool bit =(top && left  && (c != 1 && c != 2 && c != 3 && c != 7)) ||
              (top && right && (c != 5 && c != 6))                     ||
              (tiptop && middle_x && (c != 1 && c != 4))               ||
              (middle_x && middle_y && (c > 1 && c != 7))              ||
              (bottom && left && (c/2*2 == c) && c != 4)             ||
              (bottom && right && (c != 2))                            ||
              (botbot && middle_x && (c != 1 && c != 4 && c != 7));
    gl_FragColor = float(bit && true) * ON_COLOR + float(!(bit && true)) * OFF_COLOR;
}