vec4 ReadNormal(vec2 coord) {
    coord = fract(coord) * vTexCoordAM.pq + vTexCoordAM.st;
    return textureGrad(normals, coord, dcdx, dcdy);
}

vec2 GetParallaxCoord(vec2 texCoord, float parallaxFade, out float surfaceDepth) {
    vec2 coord = vTexCoord.st;
    surfaceDepth = 1.0;

    if (viewVector != viewVector) {
        return texCoord;
    }

    float sampleStep = 1.0 / PARALLAX_QUALITY;
    float currentStep = 1.0;

    vec2 scaledDir = viewVector.xy * PARALLAX_DEPTH / - viewVector.z;
    vec2 stepDir = scaledDir * sampleStep * (1.0 - parallaxFade);

    vec3 normalMap = ReadNormal(coord).xyz * 2.0 - 1.0;
    float normalCheck = normalMap.x + normalMap.y;
    if (parallaxFade >= 1.0 || normalCheck < - 1.999)
        return texCoord;

    float depth = ReadNormal(coord).a;

    for (int i = 0; i < PARALLAX_QUALITY; i ++) {
        if (currentStep <= depth)
            break;
        coord += stepDir;
        depth = ReadNormal(coord).a;
        currentStep -= sampleStep;
    }

    coord = fract(coord.st) * vTexCoordAM.pq + vTexCoordAM.st;
    surfaceDepth = currentStep;

    return coord;
}

float GetParallaxShadow(float surfaceDepth, float parallaxFade, vec2 coord, vec3 lightVec, mat3 tbn) {
    float parallaxshadow = 1.0;

    if (parallaxFade >= 1.0)
        return 1.0;

    float height = surfaceDepth;
    if (height > 1.0 - 0.5 / PARALLAX_QUALITY)
        return 1.0;

    vec3 parallaxdir = tbn * lightVec;
    parallaxdir.xy *= PARALLAX_DEPTH * SELF_SHADOW_ANGLE;
    vec2 newvTexCoord = (coord - vTexCoordAM.st) / vTexCoordAM.pq;
    float sampleStep = 0.32 / SELF_SHADOW_QUALITY;

    vec2 ptexCoord = fract(newvTexCoord + parallaxdir.xy * sampleStep) *
        vTexCoordAM.pq + vTexCoordAM.st;

    float texHeight = textureGrad(normals, coord, dcdx, dcdy).a;
    float texHeightOffset = textureGrad(normals, ptexCoord, dcdx, dcdy).a;

    float texFactor = clamp01((height - texHeightOffset) / sampleStep + 1.0);

    height = mix(height, texHeight, texFactor);

    for(int i = 0; i < SELF_SHADOW_QUALITY; i++) {
        float currentHeight = height + parallaxdir.z * sampleStep * i;
        vec2 parallaxCoord  = fract(newvTexCoord + parallaxdir.xy * i * sampleStep) *
                             vTexCoordAM.pq + vTexCoordAM.st;
        float offsetHeight  = textureGrad(normals, parallaxCoord, dcdx, dcdy).a;
        float sampleShadow  = clamp01(1.0 - (offsetHeight - currentHeight) * SELF_SHADOW_STRENGTH);

        parallaxshadow = min(parallaxshadow, sampleShadow);
        if (parallaxshadow < 0.001) break;
    }
    parallaxshadow *= parallaxshadow;

    parallaxshadow = mix(parallaxshadow, 1.0, parallaxFade);

    return parallaxshadow;
}