uniform sampler2D SCREEN_TEXTURE;
uniform highp float Strength;
const highp int SampleCount = 10; // a higher number makes the shader look better, but has a big performance impact

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