/*
** Author: Eric Veach, July 1994.
**
*/

#include "gluos.h"
#include <assert.h>
#include <stddef.h>
#include "mesh.h"
#include "tess.h"
#include "render.h"

#ifndef TRUE
#define TRUE 1
#endif
#ifndef FALSE
#define FALSE 0
#endif

/* This structure remembers the information we need about a primitive
 * to be able to render it later, once we have determined which
 * primitive is able to use the most triangles.
 */
struct FaceCount
{
    long size;           /* number of triangles used */
    GLUhalfEdge *eStart; /* edge where this primitive starts */
    void (*render)(GLUtesselator *, GLUhalfEdge *, long);
    /* routine to render this primitive */
};

static struct FaceCount MaximumFan(GLUhalfEdge *eOrig);
static struct FaceCount MaximumStrip(GLUhalfEdge *eOrig);

static void RenderFan(GLUtesselator *tess, GLUhalfEdge *eStart, long size);
static void RenderStrip(GLUtesselator *tess, GLUhalfEdge *eStart, long size);
static void RenderTriangle(GLUtesselator *tess, GLUhalfEdge *eStart, long size);

static void RenderMaximumFaceGroup(GLUtesselator *tess, GLUface *fOrig);
static void RenderLonelyTriangles(GLUtesselator *tess, GLUface *head);

/************************ Strips and Fans decomposition ******************/

/* __gl_renderMesh( tess, mesh ) takes a mesh and breaks it into triangle
 * fans, strips, and separate triangles.  A substantial effort is made
 * to use as few rendering primitives as possible (ie. to make the fans
 * and strips as large as possible).
 *
 * The rendering output is provided as callbacks (see the api).
 */
void __gl_renderMesh(GLUtesselator *tess, GLUmesh *mesh)
{
    GLUface *f;

    /* Make a list of separate triangles so we can render them all at once */
    tess->lonelyTriList = NULL;

    for (f = mesh->fHead.next; f != &mesh->fHead; f = f->next)
    {
        f->marked = FALSE;
    }
    for (f = mesh->fHead.next; f != &mesh->fHead; f = f->next)
    {
        /* We examine all faces in an arbitrary order.  Whenever we find
        * an unprocessed face F, we output a group of faces including F
        * whose size is maximum.
        */
        if (f->inside && !f->marked)
        {
            RenderMaximumFaceGroup(tess, f);
            assert(f->marked);
        }
    }
    if (tess->lonelyTriList != NULL)
    {
        RenderLonelyTriangles(tess, tess->lonelyTriList);
        tess->lonelyTriList = NULL;
    }
}

static void RenderMaximumFaceGroup(GLUtesselator *tess, GLUface *fOrig)
{
    /* We want to find the largest triangle fan or strip of unmarked faces
    * which includes the given face fOrig.  There are 3 possible fans
    * passing through fOrig (one centered at each vertex), and 3 possible
    * strips (one for each CCW permutation of the vertices).  Our strategy
    * is to try all of these, and take the primitive which uses the most
    * triangles (a greedy approach).
    */
    GLUhalfEdge *e = fOrig->anEdge;
    struct FaceCount max, newFace;

    max.size   = 1;
    max.eStart = e;
    max.render = &RenderTriangle;

    if (!tess->flagBoundary)
    {
        newFace = MaximumFan(e);
        if (newFace.size > max.size)
        {
            max = newFace;
        }
        newFace = MaximumFan(e->Lnext);
        if (newFace.size > max.size)
        {
            max = newFace;
        }
        newFace = MaximumFan(e->Lprev);
        if (newFace.size > max.size)
        {
            max = newFace;
        }

        newFace = MaximumStrip(e);
        if (newFace.size > max.size)
        {
            max = newFace;
        }
        newFace = MaximumStrip(e->Lnext);
        if (newFace.size > max.size)
        {
            max = newFace;
        }
        newFace = MaximumStrip(e->Lprev);
        if (newFace.size > max.size)
        {
            max = newFace;
        }
    }
    (*(max.render))(tess, max.eStart, max.size);
}

/* Macros which keep track of faces we have marked temporarily, and allow
 * us to backtrack when necessary.  With triangle fans, this is not
 * really necessary, since the only awkward case is a loop of triangles
 * around a single origin vertex.  However with strips the situation is
 * more complicated, and we need a general tracking method like the
 * one here.
 */
#define Marked(f) (!(f)->inside || (f)->marked)

#define AddToTrail(f, t) ((f)->trail = (t), (t) = (f), (f)->marked = TRUE)

#define FreeTrail(t)                  \
    do                                \
    {                                 \
        while ((t) != NULL)           \
        {                             \
            (t)->marked = FALSE;      \
            t           = (t)->trail; \
        }                             \
    } while (0) /* absorb trailing semicolon */

static struct FaceCount MaximumFan(GLUhalfEdge *eOrig)
{
    /* eOrig->Lface is the face we want to render.  We want to find the size
    * of a maximal fan around eOrig->Org.  To do this we just walk around
    * the origin vertex as far as possible in both directions.
    */
    struct FaceCount newFace = { 0, NULL, &RenderFan };
    GLUface *trail           = NULL;
    GLUhalfEdge *e;

    for (e = eOrig; !Marked(e->Lface); e = e->Onext)
    {
        AddToTrail(e->Lface, trail);
        ++newFace.size;
    }
    for (e = eOrig; !Marked(e->Rface); e = e->Oprev)
    {
        AddToTrail(e->Rface, trail);
        ++newFace.size;
    }
    newFace.eStart = e;
    /*LINTED*/
    FreeTrail(trail);
    return newFace;
}

#define IsEven(n) (((n)&1) == 0)

static struct FaceCount MaximumStrip(GLUhalfEdge *eOrig)
{
    /* Here we are looking for a maximal strip that contains the vertices
    * eOrig->Org, eOrig->Dst, eOrig->Lnext->Dst (in that order or the
    * reverse, such that all triangles are oriented CCW).
    *
    * Again we walk forward and backward as far as possible.  However for
    * strips there is a twist: to get CCW orientations, there must be
    * an *even* number of triangles in the strip on one side of eOrig.
    * We walk the strip starting on a side with an even number of triangles;
    * if both side have an odd number, we are forced to shorten one side.
    */
    struct FaceCount newFace = { 0, NULL, &RenderStrip };
    long headSize = 0, tailSize = 0;
    GLUface *trail = NULL;
    GLUhalfEdge *e, *eTail, *eHead;

    for (e = eOrig; !Marked(e->Lface); ++tailSize, e = e->Onext)
    {
        AddToTrail(e->Lface, trail);
        ++tailSize;
        e = e->Dprev;
        if (Marked(e->Lface))
            break;
        AddToTrail(e->Lface, trail);
    }
    eTail = e;

    for (e = eOrig; !Marked(e->Rface); ++headSize, e = e->Dnext)
    {
        AddToTrail(e->Rface, trail);
        ++headSize;
        e = e->Oprev;
        if (Marked(e->Rface))
            break;
        AddToTrail(e->Rface, trail);
    }
    eHead = e;

    newFace.size = tailSize + headSize;
    if (IsEven(tailSize))
    {
        newFace.eStart = eTail->Sym;
    }
    else if (IsEven(headSize))
    {
        newFace.eStart = eHead;
    }
    else
    {
        /* Both sides have odd length, we must shorten one of them.  In fact,
        * we must start from eHead to guarantee inclusion of eOrig->Lface.
        */
        --newFace.size;
        newFace.eStart = eHead->Onext;
    }
    /*LINTED*/
    FreeTrail(trail);
    return newFace;
}

static void RenderTriangle(GLUtesselator *tess, GLUhalfEdge *e, long size)
{
    /* Just add the triangle to a triangle list, so we can render all
    * the separate triangles at once.
    */
    assert(size == 1);
    AddToTrail(e->Lface, tess->lonelyTriList);
}

static void RenderLonelyTriangles(GLUtesselator *tess, GLUface *f)
{
    /* Now we render all the separate triangles which could not be
    * grouped into a triangle fan or strip.
    */
    GLUhalfEdge *e;
    int newState;
    int edgeState = -1; /* force edge state output for first vertex */

    CALL_BEGIN_OR_BEGIN_DATA(GL_TRIANGLES);

    for (; f != NULL; f = f->trail)
    {
        /* Loop once for each edge (there will always be 3 edges) */

        e = f->anEdge;
        do
        {
            if (tess->flagBoundary)
            {
                /* Set the "edge state" to TRUE just before we output the
                * first vertex of each edge on the polygon boundary.
                 */
                newState = !e->Rface->inside;
                if (edgeState != newState)
                {
                    edgeState = newState;
                    CALL_EDGE_FLAG_OR_EDGE_FLAG_DATA(edgeState);
                }
            }
            CALL_VERTEX_OR_VERTEX_DATA(e->Org->data);

            e = e->Lnext;
        }
        while (e != f->anEdge);
    }
    CALL_END_OR_END_DATA();
}

static void RenderFan(GLUtesselator *tess, GLUhalfEdge *e, long size)
{
    /* Render as many CCW triangles as possible in a fan starting from
    * edge "e".  The fan *should* contain exactly "size" triangles
    * (otherwise we've goofed up somewhere).
    */
    CALL_BEGIN_OR_BEGIN_DATA(GL_TRIANGLE_FAN);
    CALL_VERTEX_OR_VERTEX_DATA(e->Org->data);
    CALL_VERTEX_OR_VERTEX_DATA(e->Dst->data);

    while (!Marked(e->Lface))
    {
        e->Lface->marked = TRUE;
        --size;
        e = e->Onext;
        CALL_VERTEX_OR_VERTEX_DATA(e->Dst->data);
    }

    assert(size == 0);
    CALL_END_OR_END_DATA();
}

static void RenderStrip(GLUtesselator *tess, GLUhalfEdge *e, long size)
{
    /* Render as many CCW triangles as possible in a strip starting from
    * edge "e".  The strip *should* contain exactly "size" triangles
    * (otherwise we've goofed up somewhere).
    */
    CALL_BEGIN_OR_BEGIN_DATA(GL_TRIANGLE_STRIP);
    CALL_VERTEX_OR_VERTEX_DATA(e->Org->data);
    CALL_VERTEX_OR_VERTEX_DATA(e->Dst->data);

    while (!Marked(e->Lface))
    {
        e->Lface->marked = TRUE;
        --size;
        e = e->Dprev;
        CALL_VERTEX_OR_VERTEX_DATA(e->Org->data);
        if (Marked(e->Lface))
            break;

        e->Lface->marked = TRUE;
        --size;
        e = e->Onext;
        CALL_VERTEX_OR_VERTEX_DATA(e->Dst->data);
    }

    assert(size == 0);
    CALL_END_OR_END_DATA();
}

/************************ Boundary contour decomposition ******************/

/* __gl_renderBoundary( tess, mesh ) takes a mesh, and outputs one
 * contour for each face marked "inside".  The rendering output is
 * provided as callbacks (see the api).
 */
void __gl_renderBoundary(GLUtesselator *tess, GLUmesh *mesh)
{
    GLUface *f;
    GLUhalfEdge *e;

    for (f = mesh->fHead.next; f != &mesh->fHead; f = f->next)
    {
        if (f->inside)
        {
            CALL_BEGIN_OR_BEGIN_DATA(GL_LINE_LOOP);
            e = f->anEdge;
            do
            {
                CALL_VERTEX_OR_VERTEX_DATA(e->Org->data);
                e = e->Lnext;
            }
            while (e != f->anEdge);
            CALL_END_OR_END_DATA();
        }
    }
}

/************************ Quick-and-dirty decomposition ******************/

#define SIGN_INCONSISTENT 2

static int ComputeNormal(GLUtesselator *tess, GLdouble norm[3], int check)
/*
 * If check==FALSE, we compute the polygon normal and place it in norm[].
 * If check==TRUE, we check that each triangle in the fan from v0 has a
 * consistent orientation with respect to norm[].  If triangles are
 * consistently oriented CCW, return 1; if CW, return -1; if all triangles
 * are degenerate return 0; otherwise (no consistent orientation) return
 * SIGN_INCONSISTENT.
 */
{
    CachedVertex *v0 = tess->cache;
    CachedVertex *vn = v0 + tess->cacheCount;
    CachedVertex *vc;
    GLdouble dot, xc, yc, zc, xp, yp, zp, n[3];
    int sign = 0;

    /* Find the polygon normal.  It is important to get a reasonable
    * normal even when the polygon is self-intersecting (eg. a bowtie).
    * Otherwise, the computed normal could be very tiny, but perpendicular
    * to the true plane of the polygon due to numerical noise.  Then all
    * the triangles would appear to be degenerate and we would incorrectly
    * decompose the polygon as a fan (or simply not render it at all).
    *
    * We use a sum-of-triangles normal algorithm rather than the more
    * efficient sum-of-trapezoids method (used in CheckOrientation()
    * in normal.c).  This lets us explicitly reverse the signed area
    * of some triangles to get a reasonable normal in the self-intersecting
    * case.
    */
    if (!check)
    {
        norm[0] = norm[1] = norm[2] = 0.0;
    }

    vc = v0 + 1;
    xc = vc->coords[0] - v0->coords[0];
    yc = vc->coords[1] - v0->coords[1];
    zc = vc->coords[2] - v0->coords[2];
    while (++vc < vn)
    {
        xp = xc;
        yp = yc;
        zp = zc;
        xc = vc->coords[0] - v0->coords[0];
        yc = vc->coords[1] - v0->coords[1];
        zc = vc->coords[2] - v0->coords[2];

        /* Compute (vp - v0) cross (vc - v0) */
        n[0] = yp * zc - zp * yc;
        n[1] = zp * xc - xp * zc;
        n[2] = xp * yc - yp * xc;

        dot = n[0] * norm[0] + n[1] * norm[1] + n[2] * norm[2];
        if (!check)
        {
            /* Reverse the contribution of back-facing triangles to get
            * a reasonable normal for self-intersecting polygons (see above)
            */
            if (dot >= 0)
            {
                norm[0] += n[0];
                norm[1] += n[1];
                norm[2] += n[2];
            }
            else
            {
                norm[0] -= n[0];
                norm[1] -= n[1];
                norm[2] -= n[2];
            }
        }
        else if (dot != 0)
        {
            /* Check the new orientation for consistency with previous triangles */
            if (dot > 0)
            {
                if (sign < 0)
                    return SIGN_INCONSISTENT;
                sign = 1;
            }
            else
            {
                if (sign > 0)
                    return SIGN_INCONSISTENT;
                sign = -1;
            }
        }
    }
    return sign;
}

/* __gl_renderCache( tess ) takes a single contour and tries to render it
 * as a triangle fan.  This handles convex polygons, as well as some
 * non-convex polygons if we get lucky.
 *
 * Returns TRUE if the polygon was successfully rendered.  The rendering
 * output is provided as callbacks (see the api).
 */
GLboolean __gl_renderCache(GLUtesselator *tess)
{
    CachedVertex *v0 = tess->cache;
    CachedVertex *vn = v0 + tess->cacheCount;
    CachedVertex *vc;
    GLdouble norm[3];
    int sign;

    if (tess->cacheCount < 3)
    {
        /* Degenerate contour -- no output */
        return TRUE;
    }

    norm[0] = tess->normal[0];
    norm[1] = tess->normal[1];
    norm[2] = tess->normal[2];
    if (norm[0] == 0 && norm[1] == 0 && norm[2] == 0)
    {
        ComputeNormal(tess, norm, FALSE);
    }

    sign = ComputeNormal(tess, norm, TRUE);
    if (sign == SIGN_INCONSISTENT)
    {
        /* Fan triangles did not have a consistent orientation */
        return FALSE;
    }
    if (sign == 0)
    {
        /* All triangles were degenerate */
        return TRUE;
    }

    /* Make sure we do the right thing for each winding rule */
    switch (tess->windingRule)
    {
        case GLU_TESS_WINDING_ODD:
        case GLU_TESS_WINDING_NONZERO:
            break;
        case GLU_TESS_WINDING_POSITIVE:
            if (sign < 0)
                return TRUE;
            break;
        case GLU_TESS_WINDING_NEGATIVE:
            if (sign > 0)
                return TRUE;
            break;
        case GLU_TESS_WINDING_ABS_GEQ_TWO:
            return TRUE;
    }

    CALL_BEGIN_OR_BEGIN_DATA(tess->boundaryOnly ? GL_LINE_LOOP :
                             (tess->cacheCount > 3) ? GL_TRIANGLE_FAN : GL_TRIANGLES);

    CALL_VERTEX_OR_VERTEX_DATA(v0->data);
    if (sign > 0)
    {
        for (vc = v0 + 1; vc < vn; ++vc)
        {
            CALL_VERTEX_OR_VERTEX_DATA(vc->data);
        }
    }
    else
    {
        for (vc = vn - 1; vc > v0; --vc)
        {
            CALL_VERTEX_OR_VERTEX_DATA(vc->data);
        }
    }
    CALL_END_OR_END_DATA();
    return TRUE;
}
