// HMS MediaEngine – Gaussian Blur, vertikaler Pass (separable)
// Identisch zu horizontal.hlsl mit texel = (0, 1).

Texture2D    u_input_texture : register(t0);
SamplerState u_sampler       : register(s0);

cbuffer hms_params : register(b0)
{
    float4 u_resolution;
    float  u_time_seconds;
    float  u_delta_seconds;
    float  u_frame_index;
    float  u_layer_opacity;
    float  u_audio_rms;
    float  u_audio_peak;
    float  u_audio_bass;
    float  u_audio_mid;
    float  u_audio_treble;
    float  u_audio_beat;
    float  param_radius;
    float  u_quality_samples;
    float  _pad0;
    float  _pad1;
};

float4 mainPS(float4 pos : SV_POSITION, float2 uv : TEXCOORD0) : SV_Target
{
    float radius = max(param_radius, 0.0);
    float4 src = u_input_texture.Sample(u_sampler, uv);
    if (radius < 0.01)
    {
        return src;
    }

    float samples  = clamp(u_quality_samples, 1.0, 17.0);
    float stepSize = radius / max(samples - 1.0, 1.0);
    float2 texel   = float2(0.0, 1.0) / u_resolution.xy;

    float4 acc   = float4(0.0, 0.0, 0.0, 0.0);
    float total  = 0.0;
    [loop]
    for (float i = 0.0; i < samples; i += 1.0)
    {
        float t = i - (samples - 1.0) * 0.5;
        float w = exp(-(t * t) / (samples * 0.5));
        acc   += u_input_texture.Sample(u_sampler, uv + texel * (t * stepSize)) * w;
        total += w;
    }
    return acc / total;
}