#include "engine.h"

VARP(grass, 0, 0, 1);
VAR(dbggrass, 0, 0, 1);
VARP(grassdist, 0, 256, 10000);
FVARP(grasstaper, 0, 0.2, 1);
FVARP(grassstep, 0.5, 2, 8);
VARP(grassheight, 1, 4, 64);

#define NUMGRASSWEDGES 8

static struct grasswedge
{
    vec dir, across, edge1, edge2;
    plane bound1, bound2;

    grasswedge(int i) :
      dir(2*M_PI*(i+0.5f)/float(NUMGRASSWEDGES), 0),
      across(2*M_PI*((i+0.5f)/float(NUMGRASSWEDGES) + 0.25f), 0),
      edge1(vec(2*M_PI*i/float(NUMGRASSWEDGES), 0).div(cos(M_PI/NUMGRASSWEDGES))),
      edge2(vec(2*M_PI*(i+1)/float(NUMGRASSWEDGES), 0).div(cos(M_PI/NUMGRASSWEDGES))),
      bound1(vec(2*M_PI*(i/float(NUMGRASSWEDGES) - 0.25f), 0), 0),
      bound2(vec(2*M_PI*((i+1)/float(NUMGRASSWEDGES) + 0.25f), 0), 0)
    {
        across.div(-across.dot(bound1));
    }
} grasswedges[NUMGRASSWEDGES] = { 0, 1, 2, 3, 4, 5, 6, 7 };

struct grassvert
{
    vec pos;
    uchar color[4];
    float u, v, lmu, lmv;
};

static vector<grassvert> grassverts;

struct grassgroup
{
    const grasstri *tri;
    float dist;
    int tex, lmtex, offset, numquads;
};

static vector<grassgroup> grassgroups;

#define NUMGRASSOFFSETS 32

static float grassoffsets[NUMGRASSOFFSETS] = { -1 }, grassanimoffsets[NUMGRASSOFFSETS];
static int lastgrassanim = -1;

VARR(grassanimmillis, 0, 3000, 60000);
FVARR(grassanimscale, 0, 0.03f, 1);

static void animategrass()
{
    loopi(NUMGRASSOFFSETS) grassanimoffsets[i] = grassanimscale*sinf(2*M_PI*(grassoffsets[i] + lastmillis/float(grassanimmillis)));
    lastgrassanim = lastmillis;
}

VARR(grassscale, 1, 2, 64);
bvec grasscolor(255, 255, 255);
HVARFR(grasscolour, 0, 0xFFFFFF, 0xFFFFFF,
{
    if(!grasscolour) grasscolour = 0xFFFFFF;
    grasscolor = bvec((grasscolour>>16)&0xFF, (grasscolour>>8)&0xFF, grasscolour&0xFF);
});
FVARR(grassalpha, 0, 1, 1);
 
static void gengrassquads(grassgroup *&group, const grasswedge &w, const grasstri &g, Texture *tex)
{
    float t = camera1->o.dot(w.dir);
    int tstep = int(ceil(t/grassstep));
    float tstart = tstep*grassstep,
          t0 = w.dir.dot(g.v[0]), t1 = w.dir.dot(g.v[1]), t2 = w.dir.dot(g.v[2]), t3 = w.dir.dot(g.v[3]),
          tmin = min(min(t0, t1), min(t2, t3)),
          tmax = max(max(t0, t1), max(t2, t3));
    if(tmax < tstart || tmin > t + grassdist) return;

    int minstep = max(int(ceil(tmin/grassstep)) - tstep, 1),
        maxstep = int(floor(min(tmax, t + grassdist)/grassstep)) - tstep,
        numsteps = maxstep - minstep + 1;
    
    float texscale = (grassscale*tex->ys)/float(grassheight*tex->xs), animscale = grassheight*texscale;
    vec tc;
    tc.cross(g.surface, w.dir).mul(texscale);

    int color = tstep + maxstep;
    if(color < 0) color = NUMGRASSOFFSETS - (-color)%NUMGRASSOFFSETS;
    color += numsteps + NUMGRASSOFFSETS - numsteps%NUMGRASSOFFSETS;

    float leftdist = t0;
    const vec *leftv = &g.v[0];
    if(t1 > leftdist) { leftv = &g.v[1]; leftdist = t1; }
    if(t2 > leftdist) { leftv = &g.v[2]; leftdist = t2; }
    if(t3 > leftdist) { leftv = &g.v[3]; leftdist = t3; }
    float rightdist = leftdist;
    const vec *rightv = leftv;

    vec across(w.across.x, w.across.y, g.surface.zdelta(w.across)), leftdir(0, 0, 0), rightdir(0, 0, 0), leftp = *leftv, rightp = *rightv;
    float taperdist = grassdist*grasstaper,
          taperscale = 1.0f / (grassdist - taperdist),
          dist = maxstep*grassstep + tstart,
          leftb = 0, rightb = 0, leftdb = 0, rightdb = 0;
    for(int i = maxstep; i >= minstep; i--, color--, leftp.add(leftdir), rightp.add(rightdir), leftb += leftdb, rightb += rightdb, dist -= grassstep)
    {
        if(dist <= leftdist)
        {
            const vec *prev = leftv;
            float prevdist = leftdist;
            if(--leftv < g.v) leftv += g.numv;
            leftdist = leftv->dot(w.dir);
            if(dist <= leftdist)
            {
                prev = leftv;
                prevdist = leftdist;
                if(--leftv < g.v) leftv += g.numv;
                leftdist = leftv->dot(w.dir);
            }
            leftdir = vec(*leftv).sub(*prev);
            leftdir.mul(grassstep/-w.dir.dot(leftdir));
            leftp = vec(leftdir).mul((prevdist - dist)/grassstep).add(*prev);
            leftb = w.bound1.dist(leftp);
            leftdb = w.bound1.dot(leftdir);
        }
        if(dist <= rightdist)
        {
            const vec *prev = rightv;
            float prevdist = rightdist;
            if(++rightv >= &g.v[g.numv]) rightv = g.v;
            rightdist = rightv->dot(w.dir);
            if(dist <= rightdist) 
            {
                prev = rightv;
                prevdist = rightdist;
                if(++rightv >= &g.v[g.numv]) rightv = g.v;
                rightdist = rightv->dot(w.dir);
            }
            rightdir = vec(*rightv).sub(*prev);
            rightdir.mul(grassstep/-w.dir.dot(rightdir));
            rightp = vec(rightdir).mul((prevdist - dist)/grassstep).add(*prev);
            rightb = w.bound2.dist(rightp);
            rightdb = w.bound2.dot(rightdir);
        }
        vec p1 = leftp, p2 = rightp;
        if(leftb > 0)
        {
            if(w.bound1.dist(p2) >= 0) continue;
            p1.add(vec(across).mul(leftb));
        } 
        if(rightb > 0)
        {
            if(w.bound2.dist(p1) >= 0) continue;
            p2.sub(vec(across).mul(rightb));
        }

        if(!group)
        {
            group = &grassgroups.add();
            group->tri = &g;
            group->tex = tex->id;
            extern bool brightengeom;
            extern int fullbright;
            int lmid = brightengeom && (g.lmid < LMID_RESERVED || (fullbright && editmode)) ? LMID_BRIGHT : g.lmid;
            group->lmtex = lightmaptexs.inrange(lmid) ? lightmaptexs[lmid].id : notexture->id;
            group->offset = grassverts.length();
            group->numquads = 0;
            if(lastgrassanim!=lastmillis) animategrass();
        }
  
        group->numquads++;
 
        float offset = grassoffsets[color%NUMGRASSOFFSETS],
              animoffset = animscale*grassanimoffsets[color%NUMGRASSOFFSETS],
              tc1 = tc.dot(p1) + offset, tc2 = tc.dot(p2) + offset,
              lm1u = g.tcu.dot(p1), lm1v = g.tcv.dot(p1),
              lm2u = g.tcu.dot(p2), lm2v = g.tcv.dot(p2),
              fade = dist - t > taperdist ? (grassdist - (dist - t))*taperscale : 1,
              height = grassheight * fade;
        uchar color[4] = { grasscolor.x, grasscolor.y, grasscolor.z, uchar(fade*grassalpha*255) };

        #define GRASSVERT(n, tcv, modify) { \
            grassvert &gv = grassverts.add(); \
            gv.pos = p##n; \
            memcpy(gv.color, color, sizeof(color)); \
            gv.u = tc##n; gv.v = tcv; \
            gv.lmu = lm##n##u; gv.lmv = lm##n##v; \
            modify; \
        }
    
        GRASSVERT(2, 0, { gv.pos.z += height; gv.u += animoffset; });
        GRASSVERT(1, 0, { gv.pos.z += height; gv.u += animoffset; });
        GRASSVERT(1, 1, );
        GRASSVERT(2, 1, );
    }
}             

static void gengrassquads(vtxarray *va)
{
    loopv(va->grasstris)
    {
        grasstri &g = va->grasstris[i];
        if(isfoggedsphere(g.radius, g.center)) continue;
        float dist = g.center.dist(camera1->o);
        if(dist - g.radius > grassdist) continue;
            
        Slot &s = *lookupvslot(g.texture, false).slot;
        if(!s.grasstex) 
        {
            if(!s.autograss) continue;
            s.grasstex = textureload(s.autograss, 2);
        }

        grassgroup *group = NULL;
        loopi(NUMGRASSWEDGES)
        {
            grasswedge &w = grasswedges[i];    
            if(w.bound1.dist(g.center) > g.radius || w.bound2.dist(g.center) > g.radius) continue;
            gengrassquads(group, w, g, s.grasstex);
        }
        if(group) group->dist = dist;
    }
}

static inline bool comparegrassgroups(const grassgroup &x, const grassgroup &y)
{
    return x.dist > y.dist;
}

void generategrass()
{
    if(!grass || !grassdist) return;

    grassgroups.setsize(0);
    grassverts.setsize(0);

    if(grassoffsets[0] < 0) loopi(NUMGRASSOFFSETS) grassoffsets[i] = rnd(0x1000000)/float(0x1000000);

    loopi(NUMGRASSWEDGES)
    {
        grasswedge &w = grasswedges[i];
        w.bound1.offset = -camera1->o.dot(w.bound1);
        w.bound2.offset = -camera1->o.dot(w.bound2);
    }

    extern vtxarray *visibleva;
    for(vtxarray *va = visibleva; va; va = va->next)
    {
        if(va->grasstris.empty() || va->occluded >= OCCLUDE_GEOM) continue;
        if(va->distance > grassdist) continue;
        if(reflecting || refracting>0 ? va->o.z+va->size<reflectz : va->o.z>=reflectz) continue;
        gengrassquads(va);
    }

    grassgroups.sort(comparegrassgroups);
}

void rendergrass()
{
    if(!grass || !grassdist || grassgroups.empty() || dbggrass) return;

    glDisable(GL_CULL_FACE);
    glEnable(GL_BLEND);
    glBlendFunc(renderpath==R_FIXEDFUNCTION ? GL_SRC_ALPHA : GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glDepthMask(GL_FALSE);

    SETSHADER(grass);

    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(3, GL_FLOAT, sizeof(grassvert), grassverts[0].pos.v);

    glEnableClientState(GL_COLOR_ARRAY);
    glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(grassvert), grassverts[0].color);

    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glTexCoordPointer(2, GL_FLOAT, sizeof(grassvert), &grassverts[0].u);

    if(renderpath!=R_FIXEDFUNCTION || maxtmus>=2)
    {
        glActiveTexture_(GL_TEXTURE1_ARB);
        glClientActiveTexture_(GL_TEXTURE1_ARB);
        glEnable(GL_TEXTURE_2D);
        glEnableClientState(GL_TEXTURE_COORD_ARRAY);
        glTexCoordPointer(2, GL_FLOAT, sizeof(grassvert), &grassverts[0].lmu);
        if(renderpath==R_FIXEDFUNCTION) setuptmu(1, "P * T x 2"); 
        glClientActiveTexture_(GL_TEXTURE0_ARB);
        glActiveTexture_(GL_TEXTURE0_ARB);
    }

    int texid = -1, lmtexid = -1;
    loopv(grassgroups)
    {
        grassgroup &g = grassgroups[i];

        if(reflecting || refracting)
        {
            if(refracting < 0 ? g.tri->minz > reflectz : g.tri->maxz + grassheight < reflectz) continue;
            if(isfoggedsphere(g.tri->radius, g.tri->center)) continue;
        }

        if(texid != g.tex)
        {
            glBindTexture(GL_TEXTURE_2D, g.tex);
            texid = g.tex;
        }
        if(lmtexid != g.lmtex)
        {
            if(renderpath!=R_FIXEDFUNCTION || maxtmus>=2)
            {
                glActiveTexture_(GL_TEXTURE1_ARB);
                glBindTexture(GL_TEXTURE_2D, g.lmtex);
                glActiveTexture_(GL_TEXTURE0_ARB);
            }
            lmtexid = g.lmtex;
        }

        glDrawArrays(GL_QUADS, g.offset, 4*g.numquads);
        xtravertsva += 4*g.numquads;
    }

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_COLOR_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);

    if(renderpath!=R_FIXEDFUNCTION || maxtmus>=2)
    {
        glActiveTexture_(GL_TEXTURE1_ARB);
        glClientActiveTexture_(GL_TEXTURE1_ARB);
        if(renderpath==R_FIXEDFUNCTION) resettmu(1);
        glDisableClientState(GL_TEXTURE_COORD_ARRAY);
        glDisable(GL_TEXTURE_2D);
        glClientActiveTexture_(GL_TEXTURE0_ARB);
        glActiveTexture_(GL_TEXTURE0_ARB);
    }

    glDisable(GL_BLEND);
    glDepthMask(GL_TRUE);
    glEnable(GL_CULL_FACE);
}

