util.h

/* Copyright (c) 2007 Scott Lembcke
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

// These are utility routines to use when creating custom constraints.
// I'm not sure if this should be part of the private API or not.
// I should probably clean up the naming conventions if it is...

#define CP_DefineClassGetter(t) const cpConstraintClass * t##GetClass(void){return (cpConstraintClass *)&klass;}

void cpConstraintInit(cpConstraint *constraint, const cpConstraintClass *klass, cpBody *a, cpBody *b);

static inline cpVect
relative_velocity(cpBody *a, cpBody *b, cpVect r1, cpVect r2){
  cpVect v1_sum = cpvadd(a->v, cpvmult(cpvperp(r1), a->w));
  cpVect v2_sum = cpvadd(b->v, cpvmult(cpvperp(r2), b->w));
  
  return cpvsub(v2_sum, v1_sum);
}

static inline cpFloat
normal_relative_velocity(cpBody *a, cpBody *b, cpVect r1, cpVect r2, cpVect n){
  return cpvdot(relative_velocity(a, b, r1, r2), n);
}

static inline void
apply_impulse(cpBody *body, cpVect j, cpVect r){
  body->v = cpvadd(body->v, cpvmult(j, body->m_inv));
  body->w += body->i_inv*cpvcross(r, j);
}

static inline void
apply_impulses(cpBody *a , cpBody *b, cpVect r1, cpVect r2, cpVect j)
{
  apply_impulse(a, cpvneg(j), r1);
  apply_impulse(b, j, r2);
}

static inline void
apply_bias_impulse(cpBody *body, cpVect j, cpVect r)
{
  body->CP_PRIVATE(v_bias) = cpvadd(body->CP_PRIVATE(v_bias), cpvmult(j, body->m_inv));
  body->CP_PRIVATE(w_bias) += body->i_inv*cpvcross(r, j);
}

static inline void
apply_bias_impulses(cpBody *a , cpBody *b, cpVect r1, cpVect r2, cpVect j)
{
  apply_bias_impulse(a, cpvneg(j), r1);
  apply_bias_impulse(b, j, r2);
}

static inline cpFloat
k_scalar_body(cpBody *body, cpVect r, cpVect n)
{
  cpFloat rcn = cpvcross(r, n);
  return body->m_inv + body->i_inv*rcn*rcn;
}

static inline cpFloat
k_scalar(cpBody *a, cpBody *b, cpVect r1, cpVect r2, cpVect n)
{
  cpFloat value = k_scalar_body(a, r1, n) + k_scalar_body(b, r2, n);
  cpAssertSoft(value != 0.0, "Unsolvable collision or constraint.");
  
  return value;
}

static inline cpMat2x2
k_tensor(cpBody *a, cpBody *b, cpVect r1, cpVect r2)
{
  cpFloat m_sum = a->m_inv + b->m_inv;
  
  // start with Identity*m_sum
  cpFloat k11 = m_sum, k12 = 0.0f;
  cpFloat k21 = 0.0f,  k22 = m_sum;
  
  // add the influence from r1
  cpFloat a_i_inv = a->i_inv;
  cpFloat r1xsq =  r1.x * r1.x * a_i_inv;
  cpFloat r1ysq =  r1.y * r1.y * a_i_inv;
  cpFloat r1nxy = -r1.x * r1.y * a_i_inv;
  k11 += r1ysq; k12 += r1nxy;
  k21 += r1nxy; k22 += r1xsq;
  
  // add the influnce from r2
  cpFloat b_i_inv = b->i_inv;
  cpFloat r2xsq =  r2.x * r2.x * b_i_inv;
  cpFloat r2ysq =  r2.y * r2.y * b_i_inv;
  cpFloat r2nxy = -r2.x * r2.y * b_i_inv;
  k11 += r2ysq; k12 += r2nxy;
  k21 += r2nxy; k22 += r2xsq;
  
  // invert
  cpFloat det = k11*k22 - k12*k21;
  cpAssertSoft(det != 0.0, "Unsolvable constraint.");
  
  cpFloat det_inv = 1.0f/det;
  return cpMat2x2New(
     k22*det_inv, -k12*det_inv,
    -k21*det_inv,  k11*det_inv
  );
}

static inline cpFloat
bias_coef(cpFloat errorBias, cpFloat dt)
{
  return 1.0f - cpfpow(errorBias, dt);
}