#version 300 es
precision highp float;   // highp: fullscreen UV addressing (mediump fp16 is not enough on mobile)

in  vec2 vTexCoord;
out vec4 fragColor;

uniform mediump sampler2D u_tex;
uniform vec2      u_center;    // 0..1 UV
uniform float     u_strength;  // 0..0.5 typical
uniform int       u_samples;   // 2..16

const int MAX_SAMPLES = 16;

void main()
{
    vec2 dir = vTexCoord - u_center;
    vec3 acc = vec3(0.0);
    int n = clamp(u_samples, 1, MAX_SAMPLES);
    float invN = 1.0 / float(n);

    for (int i = 0; i < MAX_SAMPLES; ++i)
    {
        if (i >= n) break;
        float t = float(i) * invN * u_strength;
        acc += texture(u_tex, vTexCoord - dir * t).rgb;
    }

    fragColor = vec4(acc * invN, 1.0);
}