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

in vec2 vTexCoord;
uniform mediump sampler2D u_tex;
uniform vec2 u_direction;   // (texelSize.x, 0) for H, (0, texelSize.y) for V
out vec4 fragColor;

// 9-tap Gaussian (sigma ≈ 2) in 5 fetches: each side-tap pair collapses into one bilinear fetch
// at the weight-averaged offset — requires GL_LINEAR filtering on the source
const float w0 = 0.2270270270;
const float w1 = 0.3162162162;   // taps 1+2 combined
const float w2 = 0.0702702703;   // taps 3+4 combined
const float o1 = 1.3846153846;
const float o2 = 3.2307692308;

void main() {
    vec3 result = texture(u_tex, vTexCoord).rgb * w0;
    vec2 d = u_direction;

    result += texture(u_tex, vTexCoord + d * o1).rgb * w1;
    result += texture(u_tex, vTexCoord - d * o1).rgb * w1;
    result += texture(u_tex, vTexCoord + d * o2).rgb * w2;
    result += texture(u_tex, vTexCoord - d * o2).rgb * w2;

    fragColor = vec4(result, 1.0);
}