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// Based on http://kodemongki.blogspot.com/2011/06/kameraku-custom-shader-effects-example.html

#ifdef GL_ES
    precision mediump float;
#else
#   define lowp
#   define mediump
#   define highp
#endif // GL_ES

uniform float grid;
uniform float step_x;
uniform float step_y;

uniform sampler2D source;
uniform lowp float qt_Opacity;
varying vec2 qt_TexCoord0;

void main()
{
    vec2 uv = qt_TexCoord0.xy;
    float offx = floor(uv.x  / (grid * step_x));
    float offy = floor(uv.y  / (grid * step_y));
    vec3 res = texture2D(source, vec2(offx * grid * step_x , offy * grid * step_y)).rgb;
    vec2 prc = fract(uv / vec2(grid * step_x, grid * step_y));
    vec2 pw = pow(abs(prc - 0.5), vec2(2.0));
    float  rs = pow(0.45, 2.0);
    float gr = smoothstep(rs - 0.1, rs + 0.1, pw.x + pw.y);
    float y = (res.r + res.g + res.b) / 3.0;
    vec3 ra = res / y;
    float ls = 0.3;
    float lb = ceil(y / ls);
    float lf = ls * lb + 0.3;
    res = lf * res;
    vec3 col = mix(res, vec3(0.1, 0.1, 0.1), gr);
    gl_FragColor = qt_Opacity * vec4(col, 1.0);
}
