precision mediump float;

uniform vec4 dimensions;
uniform float pixelSize;
uniform sampler2D uSampler;

float character(float n, vec2 p)
{
    p = floor(p*vec2(4.0, -4.0) + 2.5);
    if (clamp(p.x, 0.0, 4.0) == p.x && clamp(p.y, 0.0, 4.0) == p.y)
    {
        if (int(mod(n/exp2(p.x + 5.0*p.y), 2.0)) == 1) return 1.0;
    }
    return 0.0;
}

void main()
{
    vec2 uv = gl_FragCoord.xy;

    vec3 col = texture2D(uSampler, floor( uv / pixelSize ) * pixelSize / dimensions.xy).rgb;

    float gray = (col.r + col.g + col.b) / 3.0;

    float n =  65536.0;             // .
    if (gray > 0.2) n = 65600.0;    // :
    if (gray > 0.3) n = 332772.0;   // *
    if (gray > 0.4) n = 15255086.0; // o
    if (gray > 0.5) n = 23385164.0; // &
    if (gray > 0.6) n = 15252014.0; // 8
    if (gray > 0.7) n = 13199452.0; // @
    if (gray > 0.8) n = 11512810.0; // #

    vec2 p = mod( uv / ( pixelSize * 0.5 ), 2.0) - vec2(1.0);
    col = col * character(n, p);

    gl_FragColor = vec4(col, 1.0);
}