// -*- mode: c++ -*-
/*
  Copyright (c) 2010-2011, Intel Corporation
  All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.

    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.

    * Neither the name of Intel Corporation nor the names of its
      contributors may be used to endorse or promote products derived from
      this software without specific prior written permission.


   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
   IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
   PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
   OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  
*/
/*
  Based on Syoyo Fujita's aobench: http://code.google.com/p/aobench
*/

#define NAO_SAMPLES		8
#define M_PI 3.1415926535f

typedef float<3> vec;

struct Isect {
    float      t;
    vec        p;
    vec        n;
    int        hit; 
};

struct Sphere {
    vec        center;
    float      radius;

};

struct Plane {
    vec    p;
    vec    n;
};

struct Ray {
    vec org;
    vec dir;
};

static inline float dot(vec a, vec b) {
    return a.x * b.x + a.y * b.y + a.z * b.z;
}

static inline vec vcross(vec v0, vec v1) {
    vec ret;
    ret.x = v0.y * v1.z - v0.z * v1.y;
    ret.y = v0.z * v1.x - v0.x * v1.z;
    ret.z = v0.x * v1.y - v0.y * v1.x;
    return ret;
}

static inline void vnormalize(vec &v) {
    float len2 = dot(v, v);
    float invlen = rsqrt(len2);
    v *= invlen;
}


static inline void
ray_plane_intersect(Isect &isect, Ray &ray, Plane &plane) {
    float d = -dot(plane.p, plane.n);
    float v = dot(ray.dir, plane.n);

    cif (abs(v) < 1.0e-17) 
        return;
    else {
        float t = -(dot(ray.org, plane.n) + d) / v;

        cif ((t > 0.0) && (t < isect.t)) {
            isect.t = t;
            isect.hit = 1;
            isect.p = ray.org + ray.dir * t;
            isect.n = plane.n;
        }
    }
}


static inline void
ray_sphere_intersect(Isect &isect, Ray &ray, Sphere &sphere) {
    vec rs = ray.org - sphere.center;

    float B = dot(rs, ray.dir);
    float C = dot(rs, rs) - sphere.radius * sphere.radius;
    float D = B * B - C;

    cif (D > 0.) {
        float t = -B - sqrt(D);

        cif ((t > 0.0) && (t < isect.t)) {
            isect.t = t;
            isect.hit = 1;
            isect.p = ray.org + t * ray.dir;
            isect.n = isect.p - sphere.center;
            vnormalize(isect.n);
        }
    }
}


static inline void
orthoBasis(vec basis[3], vec n) {
    basis[2] = n;
    basis[1].x = 0.0; basis[1].y = 0.0; basis[1].z = 0.0;

    if ((n.x < 0.6) && (n.x > -0.6)) {
        basis[1].x = 1.0;
    } else if ((n.y < 0.6) && (n.y > -0.6)) {
        basis[1].y = 1.0;
    } else if ((n.z < 0.6) && (n.z > -0.6)) {
        basis[1].z = 1.0;
    } else {
        basis[1].x = 1.0;
    }

    basis[0] = vcross(basis[1], basis[2]);
    vnormalize(basis[0]);

    basis[1] = vcross(basis[2], basis[0]);
    vnormalize(basis[1]);
}


static inline float
ambient_occlusion(Isect &isect, Plane &plane, Sphere spheres[3], 
                  RNGState &rngstate) {
    float eps = 0.0001f;
    vec p, n;
    vec basis[3];
    float occlusion = 0.0;

    p = isect.p + eps * isect.n;

    orthoBasis(basis, isect.n);

    static const uniform int ntheta = NAO_SAMPLES;
    static const uniform int nphi   = NAO_SAMPLES;
    for (uniform int j = 0; j < ntheta; j++) {
        for (uniform int i = 0; i < nphi; i++) {
            Ray ray;
            Isect occIsect;

            float theta = sqrt(frandom(&rngstate));
            float phi   = 2.0f * M_PI * frandom(&rngstate);
            float x = cos(phi) * theta;
            float y = sin(phi) * theta;
            float z = sqrt(1.0 - theta * theta);

            // local . global
            float rx = x * basis[0].x + y * basis[1].x + z * basis[2].x;
            float ry = x * basis[0].y + y * basis[1].y + z * basis[2].y;
            float rz = x * basis[0].z + y * basis[1].z + z * basis[2].z;

            ray.org = p;
            ray.dir.x = rx;
            ray.dir.y = ry;
            ray.dir.z = rz;

            occIsect.t   = 1.0e+17;
            occIsect.hit = 0;

            for (uniform int snum = 0; snum < 3; ++snum)
                ray_sphere_intersect(occIsect, ray, spheres[snum]); 
            ray_plane_intersect (occIsect, ray, plane); 

            if (occIsect.hit) occlusion += 1.0;
        }
    }

    occlusion = (ntheta * nphi - occlusion) / (float)(ntheta * nphi);
    return occlusion;
}


/* Compute the image for the scanlines from [y0,y1), for an overall image
   of width w and height h.
 */
static void ao_scanlines(uniform int y0, uniform int y1, uniform int w, 
                         uniform int h,  uniform int nsubsamples, 
                         uniform float image[]) {
    static Plane plane = { { 0.0f, -0.5f, 0.0f }, { 0.f, 1.f, 0.f } };
    static Sphere spheres[3] = {
        { { -2.0f, 0.0f, -3.5f }, 0.5f },
        { { -0.5f, 0.0f, -3.0f }, 0.5f },
        { { 1.0f, 0.0f, -2.2f }, 0.5f } };
    RNGState rngstate;

    seed_rng(&rngstate, programIndex + (y0 << (programIndex & 15)));

    // Compute the mapping between the 'programCount'-wide program
    // instances running in parallel and samples in the image.  
    //
    // For now, we'll always take four samples per pixel, so start by
    // initializing du and dv with offsets into subpixel samples.  We'll
    // take care of further updating du and dv for the case where we're
    // doing more than 4 program instances in parallel shortly.
    uniform float uSteps[4] = { 0, 1, 0, 1 };
    uniform float vSteps[4] = { 0, 0, 1, 1 };
    float du = uSteps[programIndex % 4] / nsubsamples;
    float dv = vSteps[programIndex % 4] / nsubsamples;

    // Now handle the case where we are able to do more than one pixel's
    // worth of work at once.  nx records the number of pixels in the x
    // direction we do per iteration and ny the number in y.
    uniform int nx = 1, ny = 1;

    // FIXME: We actually need ny to be 1 regardless of the decomposition,
    // since the task decomposition is one scanline high.

    if (programCount == 8) {
        // Do two pixels at once in the x direction
        nx = 2;
        if (programIndex >= 4) 
            // And shift the offsets for the second pixel's worth of work
            ++du;
    }
    else if (programCount == 16) {
        nx = 4;
        ny = 1;
        if (programIndex >= 4 && programIndex < 8)
            ++du;
        if (programIndex >= 8 && programIndex < 12)
            du += 2;
        if (programIndex >= 12)
            du += 3;
    }

    // Now loop over all of the pixels, stepping in x and y as calculated
    // above.  (Assumes that ny divides y and nx divides x...)
    for (uniform int y = y0; y < y1; y += ny) {
        for (uniform int x = 0; x < w; x += nx)  {
            // Figure out x,y pixel in NDC
            float px =  (x + du - (w / 2.0f)) / (w / 2.0f);
            float py = -(y + dv - (h / 2.0f)) / (h / 2.0f);
            float ret = 0.f;
            Ray ray;
            Isect isect;

            ray.org = 0.f;

            // Poor man's perspective projection
            ray.dir.x = px;
            ray.dir.y = py;
            ray.dir.z = -1.0;
            vnormalize(ray.dir);

            isect.t   = 1.0e+17;
            isect.hit = 0;

            for (uniform int snum = 0; snum < 3; ++snum)
                ray_sphere_intersect(isect, ray, spheres[snum]);
            ray_plane_intersect(isect, ray, plane);

            // Note use of 'coherent' if statement; the set of rays we
            // trace will often all hit or all miss the scene
            cif (isect.hit)
                ret = ambient_occlusion(isect, plane, spheres, rngstate);

            // This is a little grungy; we have results for
            // programCount-worth of values.  Because we're doing 2x2
            // subsamples, we need to peel them off in groups of four,
            // average the four values for each pixel, and update the
            // output image.
            //
            // Store the varying value to a uniform array of the same size.
            // See the discussion about communication among program
            // instances in the ispc user's manual for more discussion on
            // this idiom.
            uniform float retArray[programCount];
            retArray[programIndex] = ret;

            // offset to the first pixel in the image
            uniform int offset = 3 * (y * w + x);
            for (uniform int p = 0; p < programCount; p += 4, offset += 3) {
                // Get the four sample values for this pixel
                uniform float sumret = retArray[p] + retArray[p+1] + retArray[p+2] +
                    retArray[p+3];

                // Normalize by number of samples taken
                sumret /= nsubsamples * nsubsamples; 
                
                // Store result in the image
                image[offset+0] = sumret;
                image[offset+1] = sumret;
                image[offset+2] = sumret;
            }
        }
    }
}


export void ao_ispc(uniform int w, uniform int h, uniform int nsubsamples, 
                    uniform float image[]) {
    ao_scanlines(0, h, w, h, nsubsamples, image);
}


static void task ao_task(uniform int width, uniform int height, 
                         uniform int nsubsamples, uniform float image[]) {
    ao_scanlines(taskIndex, taskIndex+1, width, height, nsubsamples, image);
}


export void ao_ispc_tasks(uniform int w, uniform int h, uniform int nsubsamples, 
                          uniform float image[]) {
    launch[h] ao_task(w, h, nsubsamples, image);
}
