// ═══════════════════════════════════════════════════════════════
// ODIX Halation v1.0
// Film halation simulation — warm highlight bleed
//
// Halation is caused by light passing through film emulsion,
// reflecting off the film base, and re-exposing the emulsion
// from behind. It creates warm, soft glows around bright areas —
// particularly light sources and specular highlights.
//
// USAGE — Two modes:
//
//   MODE A — Full halation (recommended):
//     1. Duplicate your node.
//     2. On the duplicate: add a Gaussian Blur (4–10px).
//     3. Apply this DCTL AFTER the blur.
//     4. Composite back over the original with Screen or Add
//        blend mode at 30–60% opacity.
//
//   MODE B — Standalone color shift only:
//     Apply directly. No blur. Adds warm highlight shift without
//     spatial spread. Useful for subtle warmth on highlights.
//
// PARAMETERS:
//   Threshold     — luminance level where halation starts (0=black, 1=white)
//   Knee Softness — how gradually it rolls into the threshold
//   Warmth        — intensity of the warm color shift
//   Color Temp    — 0=cool blue halation (rare), 1=warm orange-red (typical)
//   Bleed Mix     — how much the color bleeds toward the halation color
//   Strength      — master blend control
//
// COLOR SPACE:
//   Scene-linear. Place before output LUT.
//   Works in log but reduce Threshold to 0.5–0.65 range.
//
// by Odbat Batsaikhan — odixbat.com — @odixbat
// ═══════════════════════════════════════════════════════════════

DEFINE_UI_PARAMS(p_Threshold,  Threshold,        DCTLUI_SLIDER_FLOAT, 0.72, 0.2,  1.0, 0.01)
DEFINE_UI_PARAMS(p_Knee,       Knee Softness,     DCTLUI_SLIDER_FLOAT, 0.22, 0.01, 0.6, 0.01)
DEFINE_UI_PARAMS(p_Warmth,     Warmth,            DCTLUI_SLIDER_FLOAT, 0.55, 0.0,  1.0, 0.01)
DEFINE_UI_PARAMS(p_ColorTemp,  Color Temperature, DCTLUI_SLIDER_FLOAT, 0.72, 0.0,  1.0, 0.01)
DEFINE_UI_PARAMS(p_BleedMix,   Bleed Mix,         DCTLUI_SLIDER_FLOAT, 0.35, 0.0,  1.0, 0.01)
DEFINE_UI_PARAMS(p_Strength,   Strength,          DCTLUI_SLIDER_FLOAT, 0.6,  0.0,  1.0, 0.01)
DEFINE_UI_PARAMS(p_ChromaBoost,Chroma Lift,       DCTLUI_SLIDER_FLOAT, 0.12, 0.0,  0.5, 0.01)

__DEVICE__ float softKnee(float x, float threshold, float knee) {
    float lo = threshold - knee;
    float hi = threshold + knee;
    if (x <= lo) return 0.0f;
    if (x >= hi) return x - threshold;
    float t = (x - lo) / (2.0f * knee + 0.00001f);
    return t * t * knee;
}

__DEVICE__ float3 transform(int p_Width, int p_Height, int p_X, int p_Y, float p_R, float p_G, float p_B) {
    // Luminance for mask
    float luma = 0.2126f * p_R + 0.7152f * p_G + 0.0722f * p_B;

    // Highlight mask using soft knee
    float kneeOut = softKnee(luma, p_Threshold, p_Knee);
    float mask    = _clampf(kneeOut / (p_Knee + 0.00001f), 0.0f, 1.0f);

    // Halation color: film base reflects red-orange light
    // ColorTemp: 0.0 = blue-ish (rare, cold film stocks), 1.0 = red-orange (typical)
    float haloR = 0.85f + p_ColorTemp * 0.15f;
    float haloG = 0.30f + p_ColorTemp * 0.05f - (1.0f - p_ColorTemp) * 0.1f;
    float haloB = 0.05f + (1.0f - p_ColorTemp) * 0.55f;

    // Normalize halation color
    float haloMax = _fmaxf(haloR, _fmaxf(haloG, haloB));
    haloR /= haloMax;
    haloG /= haloMax;
    haloB /= haloMax;

    // Bleed: shift pixel color toward halation color in highlight areas
    float bleedR = p_R + (haloR * luma - p_R) * p_BleedMix * mask;
    float bleedG = p_G + (haloG * luma - p_G) * p_BleedMix * mask;
    float bleedB = p_B + (haloB * luma - p_B) * p_BleedMix * mask;

    // Add warmth glow on top
    float glowR = bleedR + haloR * mask * p_Warmth * 0.18f;
    float glowG = bleedG + haloG * mask * p_Warmth * 0.08f;
    float glowB = bleedB + haloB * mask * p_Warmth * 0.03f;

    // Slight chroma/saturation lift in near-threshold areas (border glow)
    float borderMask = mask * (1.0f - mask) * 4.0f; // peaks at mid-mask
    float lumaG = 0.2126f * glowR + 0.7152f * glowG + 0.0722f * glowB;
    glowR = lumaG + (glowR - lumaG) * (1.0f + p_ChromaBoost * borderMask);
    glowG = lumaG + (glowG - lumaG) * (1.0f + p_ChromaBoost * borderMask);
    glowB = lumaG + (glowB - lumaG) * (1.0f + p_ChromaBoost * borderMask);

    // Master blend
    float r = p_R + (glowR - p_R) * p_Strength;
    float g = p_G + (glowG - p_G) * p_Strength;
    float b = p_B + (glowB - p_B) * p_Strength;

    return make_float3(r, g, b);
}