Descent3/renderer/HardwareClipper.cpp

/*
* Descent 3 
* Copyright (C) 2024 Parallax Software
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "RendererConfig.h"
#ifndef USE_SOFTWARE_TNL

#include "pserror.h"
#include "3d.h"
#include "HardwareInternal.h"

static int free_point_num = -1;
static g3Point temp_points[MAX_POINTS_IN_POLY];
static g3Point *free_points[MAX_POINTS_IN_POLY];
vector Clip_plane_point;

void InitFreePoints(void) {
  int i;

  for (i = 0; i < MAX_POINTS_IN_POLY; i++) {
    free_points[i] = &temp_points[i];
  }
  free_point_num = 0;
}

g3Point *GetTempPoint(void) {
  ASSERT(free_point_num < MAX_POINTS_IN_POLY);

  g3Point *p = free_points[free_point_num++];
  p->p3_flags = PF_TEMP_POINT;
  return p;
}

void FreeTempPoint(g3Point *p) {
  if (free_point_num < 1) {
    mprintf((1, "clipper: no temp points to free\n"));
    free_point_num = 1;
    Int3();
  }
  ASSERT(p->p3_flags & PF_TEMP_POINT);

  free_points[--free_point_num] = p;

  p->p3_flags &= ~PF_TEMP_POINT;
}

// Verify that all the temp points are free, and free them it they are not.
#ifdef _DEBUG
void CheckTempPoints(void) {
  if (free_point_num) {
    Int3();
    InitFreePoints();
  }
}
#endif

// Free up any temp points (created by the clipper) in the given pointlist
// Parameters:	pointlist - pointer to list of pointers to points, returned by g3_ClipPolygon()
//				nv - the number of points in pointlist
void g3_FreeTempPoints(g3Point **pointlist, int nv) {
  // Go through list
  int i;
  for (i = 0; i < nv; i++) {
    if (pointlist[i]->p3_flags & PF_TEMP_POINT) {
      FreeTempPoint(pointlist[i]);
    }
  }

  // Make sure all temp points are freed
  CheckTempPoints();
}

// Clips an edge against the far plane
g3Point *ClipFarEdge(g3Point *on_pnt, g3Point *off_pnt) {
  float z_on = on_pnt->p3_z;
  float z_off = off_pnt->p3_z;

  float k = 1.0f - ((z_off - Far_clip_z) / (z_off - z_on));

  g3Point *tmp = GetTempPoint();
  tmp->p3_z = on_pnt->p3_z + ((off_pnt->p3_z - on_pnt->p3_z) * k);
  tmp->p3_x = on_pnt->p3_x + ((off_pnt->p3_x - on_pnt->p3_x) * k);
  tmp->p3_y = on_pnt->p3_y + ((off_pnt->p3_y - on_pnt->p3_y) * k);

  if (on_pnt->p3_flags & PF_UV) {
    tmp->p3_u = on_pnt->p3_u + ((off_pnt->p3_u - on_pnt->p3_u) * k);
    tmp->p3_v = on_pnt->p3_v + ((off_pnt->p3_v - on_pnt->p3_v) * k);
    tmp->p3_flags |= PF_UV;
  }

  if (on_pnt->p3_flags & PF_UV2) {
    tmp->p3_u2 = on_pnt->p3_u2 + ((off_pnt->p3_u2 - on_pnt->p3_u2) * k);
    tmp->p3_v2 = on_pnt->p3_v2 + ((off_pnt->p3_v2 - on_pnt->p3_v2) * k);
    tmp->p3_flags |= PF_UV2;
  }

  if (on_pnt->p3_flags & PF_L) {
    tmp->p3_l = on_pnt->p3_l + ((off_pnt->p3_l - on_pnt->p3_l) * k);
    tmp->p3_flags |= PF_L;
  }

  if (on_pnt->p3_flags & PF_RGBA) {
    tmp->p3_r = on_pnt->p3_r + ((off_pnt->p3_r - on_pnt->p3_r) * k);
    tmp->p3_g = on_pnt->p3_g + ((off_pnt->p3_g - on_pnt->p3_g) * k);
    tmp->p3_b = on_pnt->p3_b + ((off_pnt->p3_b - on_pnt->p3_b) * k);
    tmp->p3_a = on_pnt->p3_a + ((off_pnt->p3_a - on_pnt->p3_a) * k);
    tmp->p3_flags |= PF_RGBA;
  }

  g3_CodePoint(tmp);
  return tmp;
}

// Clips an edge against the far plane
g3Point *ClipCustomEdge(g3Point *on_pnt, g3Point *off_pnt) {
  g3Point *tmp = GetTempPoint();

  vector ray_direction = off_pnt->p3_vec - on_pnt->p3_vec;
  ray_direction.x /= Matrix_scale.x;
  ray_direction.y /= Matrix_scale.y;
  ray_direction.z /= Matrix_scale.z;

  vector w = on_pnt->p3_vec - Clip_plane_point;
  w.x /= Matrix_scale.x;
  w.y /= Matrix_scale.y;
  w.z /= Matrix_scale.z;

  float k, den = -(Clip_plane * ray_direction);
  if (den == 0.0f) {
    k = 1.0f;
  } else {
    float num = Clip_plane * w;
    k = num / den;
  }

  tmp->p3_vec = on_pnt->p3_vec + ((off_pnt->p3_vec - on_pnt->p3_vec) * k);

  if (on_pnt->p3_flags & PF_UV) {
    tmp->p3_u = on_pnt->p3_u + ((off_pnt->p3_u - on_pnt->p3_u) * k);
    tmp->p3_v = on_pnt->p3_v + ((off_pnt->p3_v - on_pnt->p3_v) * k);
    tmp->p3_flags |= PF_UV;
  }

  if (on_pnt->p3_flags & PF_UV2) {
    tmp->p3_u2 = on_pnt->p3_u2 + ((off_pnt->p3_u2 - on_pnt->p3_u2) * k);
    tmp->p3_v2 = on_pnt->p3_v2 + ((off_pnt->p3_v2 - on_pnt->p3_v2) * k);
    tmp->p3_flags |= PF_UV2;
  }

  if (on_pnt->p3_flags & PF_L) {
    tmp->p3_l = on_pnt->p3_l + ((off_pnt->p3_l - on_pnt->p3_l) * k);
    tmp->p3_flags |= PF_L;
  }

  if (on_pnt->p3_flags & PF_RGBA) {
    tmp->p3_r = on_pnt->p3_r + ((off_pnt->p3_r - on_pnt->p3_r) * k);
    tmp->p3_g = on_pnt->p3_g + ((off_pnt->p3_g - on_pnt->p3_g) * k);
    tmp->p3_b = on_pnt->p3_b + ((off_pnt->p3_b - on_pnt->p3_b) * k);
    tmp->p3_a = on_pnt->p3_a + ((off_pnt->p3_a - on_pnt->p3_a) * k);
    tmp->p3_flags |= PF_RGBA;
  }

  g3_CodePoint(tmp);
  return tmp;
}

// clips an edge against one plane.
g3Point *ClipEdge(int plane_flag, g3Point *on_pnt, g3Point *off_pnt) {
  float a, b, k;
  g3Point *tmp;

  // compute clipping value k = (xs-zs) / (xs-xe-zs+ze)
  // use x or y as appropriate, and negate x/y value as appropriate

  if (plane_flag & CC_OFF_FAR) {
    return ClipFarEdge(on_pnt, off_pnt);
  }

  if ((plane_flag & CC_OFF_CUSTOM) && Clip_custom) {
    return ClipCustomEdge(on_pnt, off_pnt);
  }

  if (plane_flag & (CC_OFF_RIGHT | CC_OFF_LEFT)) {
    a = on_pnt->p3_x;
    b = off_pnt->p3_x;
  } else {
    a = on_pnt->p3_y;
    b = off_pnt->p3_y;
  }

  if (plane_flag & (CC_OFF_LEFT | CC_OFF_BOT)) {
    a = -a;
    b = -b;
  }

  k = (a - on_pnt->p3_z) / ((a - on_pnt->p3_z) - b + off_pnt->p3_z); //(xs-zs) / (xs-zs-xe+ze)

  tmp = GetTempPoint();

  tmp->p3_x = on_pnt->p3_x + ((off_pnt->p3_x - on_pnt->p3_x) * k);
  tmp->p3_y = on_pnt->p3_y + ((off_pnt->p3_y - on_pnt->p3_y) * k);

  if (plane_flag & (CC_OFF_TOP | CC_OFF_BOT)) {
    tmp->p3_z = tmp->p3_y;
  } else {
    tmp->p3_z = tmp->p3_x;
  }

  if (plane_flag & (CC_OFF_LEFT | CC_OFF_BOT)) {
    tmp->p3_z = -tmp->p3_z;
  }

  if (on_pnt->p3_flags & PF_UV) {
    tmp->p3_u = on_pnt->p3_u + ((off_pnt->p3_u - on_pnt->p3_u) * k);
    tmp->p3_v = on_pnt->p3_v + ((off_pnt->p3_v - on_pnt->p3_v) * k);

    tmp->p3_flags |= PF_UV;
  }

  if (on_pnt->p3_flags & PF_UV2) {
    tmp->p3_u2 = on_pnt->p3_u2 + ((off_pnt->p3_u2 - on_pnt->p3_u2) * k);
    tmp->p3_v2 = on_pnt->p3_v2 + ((off_pnt->p3_v2 - on_pnt->p3_v2) * k);

    tmp->p3_flags |= PF_UV2;
  }

  if (on_pnt->p3_flags & PF_L) {
    tmp->p3_l = on_pnt->p3_l + ((off_pnt->p3_l - on_pnt->p3_l) * k);
    tmp->p3_flags |= PF_L;
  }

  if (on_pnt->p3_flags & PF_RGBA) {
    tmp->p3_r = on_pnt->p3_r + ((off_pnt->p3_r - on_pnt->p3_r) * k);
    tmp->p3_g = on_pnt->p3_g + ((off_pnt->p3_g - on_pnt->p3_g) * k);
    tmp->p3_b = on_pnt->p3_b + ((off_pnt->p3_b - on_pnt->p3_b) * k);
    tmp->p3_a = on_pnt->p3_a + ((off_pnt->p3_a - on_pnt->p3_a) * k);
    tmp->p3_flags |= PF_RGBA;
  }

  g3_CodePoint(tmp);

  return tmp;
}

// clips a line to the viewing pyramid.
void ClipLine(g3Point **p0, g3Point **p1, ubyte codes_or) {
  int plane_flag;
  g3Point *old_p1;

  // might have these left over
  //(*p0)->p3_flags &= ~(PF_UV|PF_L|PF_RGBA|PF_UV2);
  //(*p1)->p3_flags &= ~(PF_UV|PF_L|PF_RGBA|PF_UV2);

  for (plane_flag = 1; plane_flag <= 32; plane_flag <<= 1) {
    if (codes_or & plane_flag) {
      if ((*p0)->p3_codes & plane_flag) {
        // swap!
        g3Point *t = *p0;
        *p0 = *p1;
        *p1 = t;
      }

      old_p1 = *p1;

      *p1 = ClipEdge(plane_flag, *p0, *p1);

      codes_or = (*p0)->p3_codes | (*p1)->p3_codes; // get new codes

      if (old_p1->p3_flags & PF_TEMP_POINT) {
        FreeTempPoint(old_p1);
      }
    }
  }
}

int ClipPlane(int plane_flag, g3Point **src, g3Point **dest, int *nv, g3Codes *cc) {
  int i, prev, next;
  g3Point **save_dest = dest;

  // Init codes
  cc->cc_and = 0xff;
  cc->cc_or = 0;

  for (i = 0, prev = *nv - 1, next = 1; i < *nv; i++) {
    if (src[i]->p3_codes & plane_flag) {
      // cur point off?
      if (!(src[prev]->p3_codes & plane_flag)) {
        // prev not off?
        *dest = ClipEdge(plane_flag, src[prev], src[i]);
        cc->cc_or |= (*dest)->p3_codes;
        cc->cc_and &= (*dest)->p3_codes;
        dest++;
      }

      if (!(src[next]->p3_codes & plane_flag)) {
        *dest = ClipEdge(plane_flag, src[next], src[i]);
        cc->cc_or |= (*dest)->p3_codes;
        cc->cc_and &= (*dest)->p3_codes;
        dest++;
      }

      // see if must free discarded point
      if (src[i]->p3_flags & PF_TEMP_POINT) {
        FreeTempPoint(src[i]);
      }
    } else {
      // cur not off, copy to dest buffer
      *dest++ = src[i];

      cc->cc_or |= src[i]->p3_codes;
      cc->cc_and &= src[i]->p3_codes;
    }

    prev = i;
    if (++next == *nv) {
      next = 0;
    }
  }

  return (dest - save_dest);
}

// temp buffers for clipping
static g3Point *Vbuf0[MAX_POINTS_IN_POLY];
static g3Point *Vbuf1[MAX_POINTS_IN_POLY];

// Clips a polygon
// Parameters:	pointlist - pointer to a list of pointers to points
//					nv - the number of points in the polygon
//					cc - the clip codes for this polygon
// Returns:	a pointer to a list of pointer of points in the clipped polygon
// NOTE: You MUST call g3_FreeTempPoints() when you're done with the clipped polygon
g3Point **g3_ClipPolygon(g3Point **pointlist, int *nv, g3Codes *cc) {
  int plane_flag;
  g3Point **dest;

  dest = Vbuf0;

  //&	ASSERT(free_point_num == 0);	//DAJ UTB CMO
  if (free_point_num != 0) {
    mprintf((1, "clipper: leftover temp point\n"));
    free_point_num = 0;
    Int3();
  }

  for (plane_flag = 1; plane_flag <= 32; plane_flag <<= 1) {
    if (cc->cc_or & plane_flag) {

      *nv = ClipPlane(plane_flag, pointlist, dest, nv, cc);

      if (cc->cc_and) // clipped away
        return dest;

      pointlist = dest;
      dest = (pointlist == Vbuf0) ? Vbuf1 : Vbuf0;
    }
  }
  return pointlist; // we swapped after we copied
}

// sets the z distance of the far clipping plane
void g3_SetFarClipZ(float z) { Far_clip_z = z; }

// Sets up a custom clipping plane - g3_StartFrame must be called before this is called
void g3_SetCustomClipPlane(ubyte state, vector *pnt, vector *normal) {
  Clip_custom = state;
  if (state) {
    vector tempv;
    vector norm = *normal;

    tempv = *pnt - View_position;
    Clip_plane_point = tempv * View_matrix;

    Clip_plane = norm * Unscaled_matrix; // View_matrix;
    vm_NormalizeVector(&Clip_plane);
  }
}

#endif