/*
    Geometry rendering.
*/

#ifndef COM_GEM_H
#define COM_GEM_H

#include "mat.h"
#include <stdint.h>

/* Projects vertex position to a clip space via reordered row-major MVP matrix.
   It skips calculation of z depth component, as we assume to never use it.
   Instead, 3rd returned component is w value, for future projection.

   We must never render from inside geometry, as it will break no Z clipping
   assumption (see com_gem_clip_vis_project()).
 */
static inline com_vec_t com_gem_vec_project_clip(com_mat_t a, com_vec_t b) {
  com_vec_t result;

#define CASE(m_c, m_n)                                                         \
  result.a[m_c] = (((int64_t)a.a[m_n * 4 + 0] * b.s.x) +                       \
                   ((int64_t)a.a[m_n * 4 + 1] * b.s.y) +                       \
                   ((int64_t)a.a[m_n * 4 + 2] * b.s.z) + a.a[m_n * 4 + 3]) >>  \
                  COM_FIX_FRACBITS;

  CASE(0, 0);
  CASE(1, 1);
  CASE(2, 3);

#undef CASE

  return result;
}

/* TODO: Move to separate render-specific file. */
/* TODO: If we clip test bounding volume of a model first we can skip
 * all clipping whatsoever, which might hold true more often, than the cost of
 * testing the volume. */

#define COM_GEM_VERTEX_UNCLIPPED (0 << 0)
#define COM_GEM_VERTEX_CLIPPED_X (1 << 0)
#define COM_GEM_VERTEX_CLIPPED_Y (1 << 1)
/* Attempt to project clip space vertex to NDC, reporting which component lies
 * outside of view. Bit test against those per component. This is needed for
 * determining new view-lying clipped triangles. */
static inline uint8_t com_gem_clip_vis_project(com_vec_t a, com_vec_t *out) {
  uint8_t mask;
  if (a.s.x < -a.s.z || a.s.x > a.s.z)
    mask ^= COM_GEM_VERTEX_CLIPPED_X;
  if (a.s.y < -a.s.z || a.s.y > a.s.z)
    mask ^= COM_GEM_VERTEX_CLIPPED_Y;
  out->a[0] = com_fix_div(a.a[0], a.a[2]);
  out->a[1] = com_fix_div(a.a[1], a.a[2]);
  return mask;
}

#endif