terrible_projector.asc

// I can't figure any good way that makes the sprite be properly positioned in place, so I am making a bad way.
// first thing, we are going to find the distance that the sprite is from the camera plane.
// this will give us a z distance
// Then we are going to use this z distance in the renderer algorithm we have for the voxel engine
// which should make it easier to find the point we are interested, in a way that moves just like the renderer we have
// this is wasteful, but we are probably not going to have many sprites anyway...

ScreenPoint* PositionBillboardX(Vec3* cam_pos, float cam_angle, float horizon, float scale_height, Vec3* obj_pos)
{
  int y_on_screen, x_on_screen; // intermediary
  ScreenPoint* p = new ScreenPoint;
  
  // just storing because we are using these values twice
  float sinphi = Maths.Sin(cam_angle);
  float cosphi = Maths.Cos(cam_angle);
  
  // relative position in x,y of the obj in relation to camera
  float bill_rel_x = obj_pos.x - cam_pos.x;
  float bill_rel_y = obj_pos.y - cam_pos.y;
  float bill_rel_z = obj_pos.z - cam_pos.z;
    
  //float rotd_x = bill_rel_x*cosphi - bill_rel_y*sinphi; // x axis in camera, but doesn't look good, discarding...
  float rotd_z = bill_rel_x*sinphi + bill_rel_y*cosphi; // distance from camera
  
  // positive means it's behind the player, so we return the position off the screen
  if(rotd_z > 0.0) {
    p.x = -2;
    p.y = -2;
    return p;
  }
  
  float z, invz_scaled;
  
  z = IntToFloat(FloatToInt(-rotd_z-1.0));
  float end_z = z + 3.0;
  
  for (;z<end_z;z+=1.0)
  {
    if(AbsF(z) <= 1.0) z = 1.0;
    invz_scaled = scale_height/z;
    
    // Find line on map. This calculation corresponds to a field of view of 90°
    float plx =  -cosphi * z - sinphi * z;
    float ply =   sinphi * z - cosphi * z;
    float prx =   cosphi * z - sinphi * z;
    float pry =  -sinphi * z - cosphi * z;
       
    // A little segment of line dx,dy that is normal to player angle, we will use to traverse from pl(x,y) to pr(x,y)
    float dx = (prx - plx) / ScreenWidth_AsFloat;
    float dy = (pry - ply) / ScreenWidth_AsFloat;
    float ddx = ClampF(2.0*AbsF(dx), 0.5, 32.0);
    float ddy = ClampF(2.0*AbsF(dy), 0.5, 32.0);
    
    // makes the camera coordinate in the same world space of the player
    plx+=cam_pos.x;
    ply+=cam_pos.y;
    
    float p_line_x = plx;
    float p_line_y = ply;
    
    y_on_screen = FloatToInt( (-bill_rel_z) * invz_scaled + horizon );
    
    for (int i=0; i<ScreenWidth; i+=1) {      
      if(p_line_x - ddx <= obj_pos.x && obj_pos.x <= p_line_x + ddx && 
        p_line_y - ddy <= obj_pos.y && obj_pos.y <= p_line_y + ddy) {
          x_on_screen = i;
          break;  
        }
      
      p_line_x = plx + dx*IntToFloat(i);
      p_line_y = ply + dy*IntToFloat(i);
    }
    if(x_on_screen != 0) break;
  } 
  
  if(x_on_screen != 0)
  {
    p.x = x_on_screen;
    p.y = y_on_screen;
    p.z = z;
    p.w = rotd_z;
  }
  else
  {
    p.x = -1;
    p.y = -1;
  }
  return p;
}