Lephisto/src/collision.c

#include "lephisto.h"
#include "log.h"
#include "collision.h"

/**
 * @brief Collide sprite at (asx, asy) in 'at' at pos 'ap' with sprite at (bsx,bsy)
 * in 'bt' at 'bp'
 *
 * @param[in] at   - Texture a.
 * @param[in] asx  - Position of x of sprite a.
 * @param[in] asy  - Position of y of sprite a.
 * @param[in] ap   - Position in space of sprite a.
 * @param[in] bt   - Texture b.
 * @param[in] bsx  - Position of x of sprite b.
 * @param[in] bsy  - Position of y of sprite b.
 * @param[in] bp   - Position in space of sprite b.
 * @return 1 on collision, 0 else.
 */
int CollideSprite(const glTexture* at, const int asx, const int asy,
                  const Vec2* ap, const glTexture* bt,
                  const int bsx, const int bsy, const Vec2* bp) {

  int x,y;
  int ax1, ax2, ay1, ay2;
  int bx1, bx2, by1, by2;
  int inter_x0, inter_x1, inter_y0, inter_y1;
  int rasy, rbsy;
  int abx, aby, bbx, bby;

  /* a - cube coords. */
  ax1 = (int)VX(*ap) - (int)(at->sw)/2;
  ay1 = (int)VY(*ap) - (int)(at->sh)/2;
  ax2 = ax1 + (int)(at->sw) - 1;
  ay2 = ay1 + (int)(at->sh) - 1;

  /* b - cube coords. */
  bx1 = (int)VX(*bp) - (int)(bt->sw)/2;
  by1 = (int)VY(*bp) - (int)(bt->sh)/2;
  bx2 = bx1 + (int)(bt->sw) - 1;
  by2 = by1 + (int)(bt->sh) - 1;

  /* Check if bounding boxes intersect. */
  if((bx2 < ax1) || (ax2 < bx1)) return 0;
  if((by2 < ay1) || (ay2 < by1)) return 0;

  /* Define the remaining binding box. */
  inter_x0 = MAX(ax1, bx1);
  inter_x1 = MIN(ax2, bx2);
  inter_y0 = MAX(ay1, by1);
  inter_y1 = MIN(ay2, by2);

  /* Real vertical sprite value (flipped). */
  rasy = at->sy - asy - 1;
  rbsy = bt->sy - bsy - 1;

  /* Set up the base points. */
  abx = asx*(int)(at->sw)   - ax1;
  aby = rasy*(int)(at->sh)  - ay1;
  bbx = bsx*(int)(bt->sw)   - bx1;
  bby = rbsy*(int)(bt->sh)  - by1;

  for(y = inter_y0; y <= inter_y1; y++)
    for(x = inter_x0; x <= inter_x1; x++)
      /* Compute offsets for surface before passing to TransparentPixel test. */
      if((!gl_isTrans(at, abx + x, aby + y)) &&
         (!gl_isTrans(bt, bbx + x, bby + y)))
        return 1;

  return 0;
}

/**
 * @brief Calculate collision path corrections.
 *
 * @param[in] p     - Position of object that's trying to collide.
 * @param[in] v     - Velocity of object that's trying to collide.
 * @param[in] tp    - Position of the target to collide into.
 * @param[in] tv    - Velocity of the target to collide into.
 * @param[in] limit - Accuracy limit.
 * @return Direction object will need to adjust velocity to for collision.
 */
/*
 * Doesn't work as expected, needs to be fixed to allow missiles to use
 * the physics engine instead of hacking their velocities.
 */
#if 0
double CollidePath(const Vec2* p, Vec2* v,
    const Vec2* tp, Vec2* tv, double limit) {

  double mx, my;        /* Position modifiers. */
  double t, tt;         /* Time to target. */
  Vec2   test, ttest;   /* Test vector and target test vector. */
  double offset;        /* Direction to face and error it produces. */
  double mod, moddir;   /* Modifier for iteration. */
  int i;

  /* Test vector. */
  vect_cset(&test, tp->x - p->x, tp->y - p->y); /* Start byt straight line. */
  t = VMOD(test) / VMOD(*v);                    /* d=v*t ==> t=d/v. */

  /* Target test vector. */
  vectnull(&ttest); /* Starting from itself. */
  tt = VMOD(ttest) / VMOD(*tv);

  /* Special case object isn't moving. */
  if(VMOD(*v) < 1e-6)
    return VANGLE(test);

  /* Target faster than object. */
  if(VMOD(*v) < VMOD(*tv)) {
    vect_reflect(&test, v, tv);
    return VANGLE(test);
  }

  /* Loop until error is minimal. */
  offset = tt - t;
  moddir = 1.;    /* Start off by position increments. */
  mod    = 10.;   /* Start off by a 10 second jump. */
  i = 0;
  while(FABS(offset) > limit) {
    if(i > 100) break;

    /* Calculate position modifiers. */
    if(offset < -mod/2.)  /* tt>t ==> major overshot. */
      moddir = -1.;
    else if(offset < 0.) { /* tt>t ==> overshot. */
      /* Invert direction and half. */
      moddir = -1.;
      mod = mod/2.;
    }
    else if(offset > mod) /* tt<t ==> undershot. */
      moddir = 1.; /* Make sure it's positive. */
    else if(offset > 0.) { /* tt<t ==> minor undershot. */
      /* Positive and shrink step. */
      moddir = 1.;
      mod = FABS(mod)/2.;
    }
    mx = tv->x * mod * moddir;
    my = tv->y * mod * moddir;

    /* Increment test vectors. */
    vect_cadd(&test, mx, my);
    vect_cadd(&ttest, mx, my);

    /* Compare results. */
    t = VMOD(test) / VMOD(*v);
    tt = VMOD(ttest) / VMOD(*tv);
    offset = tt - t;

    i++;
  }
  return VANGLE(test);
}
#endif