OpenGL渲染与自己的Phong照明实现

Question

我已经使用以(0,0,0)为中心并直接观察球体原始的相机实现了Phong照明方案.以下是场景文件的相关内容,用于使用OpenGL查看场景以及使用我自己的实现渲染场景:

ambient 0 1 0

dir_light  1 1 1       -3 -4 -5

# A red sphere with 0.5 green ambiance, centered at (0,0,0) with radius 1
material  0 0.5 0  1 0 0    1 0 0   0 0 0  0 0 0  10 1 0
sphere   0    0 0 0    1   

由OpenGL生成的结果图像.

我的渲染应用程序生成的图像.

如您所见,两者之间存在各种差异:

1. 我的图像上的镜面高光小于OpenGL中的镜面高光.
2. 漫反射表面似乎没有以正确的方式漫射,导致黄色区域在我的图像中不必要地变大,而在OpenGL中,有一个很好的深绿色区域更接近球体的底部
3. OpenGL生成的颜色比我图像中的颜色深得多.

这些是我看到的最突出的三个差异.以下是我对Phong照明的实现:

R3Rgb Phong(R3Scene *scene, R3Ray *ray, R3Intersection *intersection)
{
  R3Rgb radiance;
  if(intersection->hit == 0)
  {
    radiance = scene->background;
    return radiance;
  }

  R3Vector normal = intersection->normal;
  R3Rgb Kd = intersection->node->material->kd;
  R3Rgb Ks = intersection->node->material->ks;

  // obtain ambient term
  R3Rgb intensity_ambient = intersection->node->material->ka*scene->ambient;

  // obtain emissive term
  R3Rgb intensity_emission = intersection->node->material->emission;

  // for each light in the scene, obtain calculate the diffuse and specular terms
  R3Rgb intensity_diffuse(0,0,0,1);
  R3Rgb intensity_specular(0,0,0,1);
  for(unsigned int i = 0; i < scene->lights.size(); i++)
  {
    R3Light *light = scene->Light(i);
    R3Rgb light_color = LightIntensity(scene->Light(i), intersection->position);
    R3Vector light_vector = -LightDirection(scene->Light(i), intersection->position);

    // calculate diffuse reflection
    intensity_diffuse += Kd*normal.Dot(light_vector)*light_color;

    // calculate specular reflection
    R3Vector reflection_vector = 2.*normal.Dot(light_vector)*normal-light_vector;
    reflection_vector.Normalize();
    R3Vector viewing_vector = ray->Start() - intersection->position;
    viewing_vector.Normalize();
    double n = intersection->node->material->shininess;
    intensity_specular += Ks*pow(max(0.,viewing_vector.Dot(reflection_vector)),n)*light_color;

  }

  radiance = intensity_emission+intensity_ambient+intensity_diffuse+intensity_specular;
  return radiance;
}

以下是相关的LightIntensity(...)和LightDirection(...)函数:

R3Vector LightDirection(R3Light *light, R3Point position)
{
  R3Vector light_direction;
  switch(light->type)
  {
    case R3_DIRECTIONAL_LIGHT:
      light_direction = light->direction;
      break;

    case R3_POINT_LIGHT:
      light_direction = position-light->position;
      break;

    case R3_SPOT_LIGHT:
      light_direction = position-light->position;
      break;
  }
  light_direction.Normalize();
  return light_direction;
}

R3Rgb LightIntensity(R3Light *light, R3Point position)
{
  R3Rgb light_intensity; 
  double distance;
  double denominator;
  if(light->type != R3_DIRECTIONAL_LIGHT)
  {
    distance = (position-light->position).Length();
    denominator = light->constant_attenuation + 
                         light->linear_attenuation*distance + 
                         light->quadratic_attenuation*distance*distance;
  }   

  switch(light->type)
  {
    case R3_DIRECTIONAL_LIGHT:
      light_intensity = light->color;
      break;

    case R3_POINT_LIGHT:
      light_intensity = light->color/denominator;
      break;

    case R3_SPOT_LIGHT:
      R3Vector from_light_to_point = position - light->position;
      light_intensity = light->color*(
                        pow(light->direction.Dot(from_light_to_point),
                            light->angle_attenuation));
      break;
  }
  return light_intensity;
}

对于任何明显的实现错误,我都非常感谢.我想知道是否可能仅仅因为OpenGL显示的伽玛值和我的显示器的默认伽玛值而发生差异.我也知道OpenGL(或至少是我提供的部分)不能在对象上投射阴影.并不是说这与所讨论的问题相关,但它只是让我想知道它是否仅仅是OpenGL与我想要做的事情之间的显示和能力差异.

谢谢您的帮助.

Answer 1

就我而言，我对伽玛值差异的最初猜测是正确的。调用渲染算法的主程序通过调用来校正图像的每个像素的 RGB 值来执行伽玛校正image->TosRGB()。注释掉调用后，我获得了OpenGL生成的图像。