uniform sampler2D SCREEN_TEXTURE;
uniform highp float VisualScale; // between 0 and 1
const highp float Intensity = 0.2;
const highp int SampleCount = 16; // multiple of 2

// a simple radial blur
void fragment() {
    highp vec2 uv = FRAGCOORD.xy * SCREEN_PIXEL_SIZE.xy;
    highp vec2 direction = vec2(0.5, 0.5) - uv;
    COLOR = vec4(0.0, 0.0, 0.0, 0.0);
    highp float test = float(SampleCount);
    for (int i=1; i <= SampleCount; i++)
    {
        COLOR += zTextureSpec(SCREEN_TEXTURE, uv + float(i) * Intensity * VisualScale / float(SampleCount) * direction);
    }
    COLOR = COLOR / float(SampleCount);
}