/*
 * CS5600 University of Utah
 * Charles McGarvey
 * mcgarvey@eng.utah.edu
 */

#ifndef _TRI_H_
#define _TRI_H_

#include "aabb.h"
#include "mat.h"
#include "vert.h"


/*
 * A triangle is a polygon of three vertices.
 */
struct tri
{
    vert_t a;
    vert_t b;
    vert_t c;
};
typedef struct tri tri_t;

/*
 * Initialize a triangle.
 */
INLINE_MAYBE
void tri_init(tri_t* t, vert_t a, vert_t b, vert_t c)
{
    t->a = a;
    t->b = b;
    t->c = c;
}


/*
 * Create a new triangle.
 */
INLINE_MAYBE
tri_t tri_new(vert_t a, vert_t b, vert_t c)
{
    tri_t t;
    tri_init(&t, a, b, c);
    return t;
}

#define TRI_ZERO tri_new(VERT_ZERO, VERT_ZERO, VERT_ZERO)


/*
 * Create a new triangle on the heap.
 */
INLINE_MAYBE
tri_t* tri_alloc(vert_t a, vert_t b, vert_t c)
{
    tri_t* t = (tri_t*)mem_alloc(sizeof(tri_t));
    tri_init(t, a, b, c);
    return t;
}


/*
 * Apply a transformation matrix to alter the triangle geometry.
 */
INLINE_MAYBE
tri_t tri_transform(tri_t t, mat_t m)
{
    t.a.v = mat_apply(m, t.a.v);
    t.b.v = mat_apply(m, t.b.v);
    t.c.v = mat_apply(m, t.c.v);
    t.a.n.w = t.b.n.w = t.c.n.w = S(0.0);
    t.a.n = vec_normalize(mat_apply(m, t.a.n));
    t.b.n = vec_normalize(mat_apply(m, t.b.n));
    t.c.n = vec_normalize(mat_apply(m, t.c.n));
    return t;
}

/*
 * Perform a homogeneous divide on the geometry.
 */
INLINE_MAYBE
tri_t tri_homodiv(tri_t t)
{
    t.a.v = vec_homodiv(t.a.v);
    t.b.v = vec_homodiv(t.b.v);
    t.c.v = vec_homodiv(t.c.v);
    return t;
}


/*
 * Calculate a normal vector.
 */
INLINE_MAYBE
vec_t tri_normal(tri_t t)
{
    vec_t n = vec_cross(vec_sub(t.b.v, t.a.v), vec_sub(t.c.v, t.a.v));
    return n;
}


/*
 * Calculate the AABB for the triangle.
 */
INLINE_MAYBE
aabb_t tri_aabb(tri_t t)
{
    aabb_t b;
    b.min = vec_new(scal_min2(t.a.v.x, t.b.v.x, t.c.v.x),
                    scal_min2(t.a.v.y, t.b.v.y, t.c.v.y),
                    scal_min2(t.a.v.z, t.b.v.z, t.c.v.z));
    b.max = vec_new(scal_max2(t.a.v.x, t.b.v.x, t.c.v.x),
                    scal_max2(t.a.v.y, t.b.v.y, t.c.v.y),
                    scal_max2(t.a.v.z, t.b.v.z, t.c.v.z));
    return b;
}


/*
 * Get the barycentric coordinates of a vector against a triangle.  The
 * returned coordinates will be a linear combination, but they may not
 * actually be barycentric coordinates.  Use the function vec_is_barycentric
 * to check if they really are barycentric coordinates, meaning the point
 * vector v is inside the triangle, ignoring the Z components.
 */
INLINE_MAYBE
bool tri_barycentric(tri_t t, scal_t* b, vec_t v)
{
    scal_t denom = (t.b.v.y - t.c.v.y) * (t.a.v.x - t.c.v.x) + (t.c.v.x - t.b.v.x) * (t.a.v.y - t.c.v.y);
    b[0] = ((t.b.v.y - t.c.v.y) * (v.x - t.c.v.x) + (t.c.v.x - t.b.v.x) * (v.y - t.c.v.y)) / denom;
    b[1] = ((t.c.v.y - t.a.v.y) * (v.x - t.c.v.x) + (t.a.v.x - t.c.v.x) * (v.y - t.c.v.y)) / denom;
    b[2] = S(1.0) - b[0] - b[1];
    if (S(0.0) <= b[0] && b[0] <= S(1.0) &&
        S(0.0) <= b[1] && b[1] <= S(1.0) &&
        S(0.0) <= b[2] && b[2] <= S(1.0)) {
        return true;
    }
    return false;
}


/*
 * Find the midpoint of the triangle.
 */
INLINE_MAYBE
vec_t tri_midpoint(tri_t t)
{
    return vec_new((t.a.v.x + t.b.v.x + t.c.v.x) * S(0.333),
                   (t.a.v.y + t.b.v.y + t.c.v.y) * S(0.333),
                   (t.a.v.z + t.b.v.z + t.c.v.z) * S(0.333));
}

/*
 * Get the average color of the triangle.
 */
INLINE_MAYBE
color_t tri_color(tri_t t)
{
    scal_t b[] = {S(0.333), S(0.333), S(0.333)};
    return color_interp2(t.a.c, t.b.c, t.c.c, b);
}


/*
 * Get an interpolated z-value at the barycentric coordinates.
 */
INLINE_MAYBE
scal_t tri_z(tri_t t, scal_t b[3])
{
    return t.a.v.z * b[0] + t.b.v.z * b[1] + t.c.v.z * b[2];
}

/*
 * Calculate an interpolated point.
 */
INLINE_MAYBE
vec_t tri_point(tri_t t, scal_t b[3])
{
    return vec_interp(t.a.v, t.b.v, t.c.v, b);
}

/*
 * Calculate an interpolated normal.
 */
INLINE_MAYBE
vec_t tri_normal2(tri_t t, scal_t b[3])
{
    return vec_normalize(vec_interp(t.a.n, t.b.n, t.c.n, b));
}

/*
 * Calculate an entirely new vertex within the triangle based on barycentric
 * coordinates.
 */
INLINE_MAYBE
vert_t tri_interp(tri_t t, scal_t b[3])
{
    vert_t v = vert_new(tri_point(t, b));
    v.c = color_interp2(t.a.c, t.b.c, t.c.c, b);
    v.n = tri_normal2(t, b);
    return v;
}


#endif // _TRI_H_