src/util/math.cpp


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#include "math.h"

#include "../render/gl_3d.h"

VEC2 m_screen_transform( const VEC3 &world ) {
  GL_DATA* gl          = gl_instance();
  MAT4* gl_proj_matrix = gl->proj_matrix;
  VEC2 screen          = gl->viewport_start;
  VEC3 clip;

  clip.x = world.x * gl_proj_matrix->m[0][0] + world.y * gl_proj_matrix->m[1][0] + world.z * gl_proj_matrix->m[2][0] + gl_proj_matrix->m[3][0];
  clip.y = world.x * gl_proj_matrix->m[0][1] + world.y * gl_proj_matrix->m[1][1] + world.z * gl_proj_matrix->m[2][1] + gl_proj_matrix->m[3][1];
  clip.z = world.x * gl_proj_matrix->m[0][3] + world.y * gl_proj_matrix->m[1][3] + world.z * gl_proj_matrix->m[2][3] + gl_proj_matrix->m[3][3];

  if( clip.z <= 0.f ) {
    screen.x = screen.y = SCREEN_INVALID_POS;
  }

  F32 ndcx = clip.x / clip.z;
  F32 ndcy = clip.y / clip.z;

  screen.x += ( ndcx * .5f + .5f ) * (F32)gl->viewport_dim.x;
  screen.y += ( 1.f - ( ndcy * .5f + .5f ) ) * (F32)gl->viewport_dim.y;

  return screen;
}