Ray Tracer Shadow Problems

Question

I am working on a ray tracer, but I am stuck for days on the shadow part. My shadow is acting really weird. Here is an image of the ray tracer:

The black part should be the shadow.

The origin of the ray is always (0.f, -10.f, -500.f), because this is a perspective projection and that is the eye of the camera. When the ray hits a plane, the hit point is always the origin of the ray, but with the sphere it is different. It is different because it is based on the position of the sphere. There is never an intersection between the plane and sphere because the origin is huge difference. I also tried to add shadow on a box, but this doesn't work either. The shadow between two spheres does work!

If someone wants to see the intersection code, let me know.

Thanks for taking the time to help me!

Camera

Camera::Camera(float a_fFov, const Dimension& a_viewDimension, vec3 a_v3Eye, vec3 a_v3Center, vec3 a_v3Up) :
m_fFov(a_fFov),
m_viewDimension(a_viewDimension),
m_v3Eye(a_v3Eye),
m_v3Center(a_v3Center),
m_v3Up(a_v3Up)
{
  // Calculate the x, y and z axis
  vec3 v3ViewDirection = (m_v3Eye - m_v3Center).normalize();
  vec3 v3U = m_v3Up.cross(v3ViewDirection).normalize();
  vec3 v3V = v3ViewDirection.cross(v3U);

  // Calculate the aspect ratio of the screen
  float fAspectRatio = static_cast<float>(m_viewDimension.m_iHeight) / 
                       static_cast<float>(m_viewDimension.m_iWidth);
  float fViewPlaneHalfWidth = tanf(m_fFov / 2.f);
  float fViewPlaneHalfHeight = fAspectRatio * fViewPlaneHalfWidth;

  // The bottom left of the plane
  m_v3ViewPlaneBottomLeft = m_v3Center - v3V * fViewPlaneHalfHeight - v3U * fViewPlaneHalfWidth;

  // The amount we need to increment to get the direction. The width and height are based on the field of view.
  m_v3IncrementX = (v3U * 2.f * fViewPlaneHalfWidth);
  m_v3IncrementY = (v3V * 2.f * fViewPlaneHalfHeight);
}

Camera::~Camera()
{
}

const Ray Camera::GetCameraRay(float iPixelX, float iPixelY) const
{
  vec3 v3Target = m_v3ViewPlaneBottomLeft + m_v3IncrementX * iPixelX + m_v3IncrementY * iPixelY;
  vec3 v3Direction = (v3Target - m_v3Eye).normalize();

  return Ray(m_v3Eye, v3Direction);
}

Camera setup

Scene::Scene(const Dimension& a_Dimension) :
m_Camera(1.22173f, a_Dimension, vec3(0.f, -10.f, -500.f), vec3(0.f, 0.f, 0.f), vec3(0.f, 1.f, 0.f))
{
  // Setup sky light
  Color ambientLightColor(0.2f, 0.1f, 0.1f);
  m_AmbientLight = new AmbientLight(0.1f, ambientLightColor);

  // Setup shapes
  CreateShapes();

  // Setup lights
  CreateLights();

  // Setup buas
  m_fBias = 1.f;
}

Scene objects

Sphere* sphere2 = new Sphere();
sphere2->SetRadius(50.f);
sphere2->SetCenter(vec3(0.f, 0.f, 0.f));
sphere2->SetMaterial(matte3);

Plane* plane = new Plane(true);
plane->SetNormal(vec3(0.f, 1.f, 0.f));
plane->SetPoint(vec3(0.f, 0.f, 0.f));
plane->SetMaterial(matte1);

Scene light

PointLight* pointLight1 = new PointLight(1.f, Color(0.1f, 0.5f, 0.7f), vec3(0.f, -200.f, 0.f), 1.f, 0.09f, 0.032f);

Shade function

for (const Light* light : a_Lights) {
    vec3 v3LightDirection = (light->m_v3Position - a_Contact.m_v3Hitpoint).normalized();

    light->CalcDiffuseLight(a_Contact.m_v3Point, a_Contact.m_v3Normal, m_fKd, lightColor);

    Ray lightRay(a_Contact.m_v3Point + a_Contact.m_v3Normal * a_fBias, v3LightDirection);

    bool test = a_RayTracer.ShadowTrace(lightRay, a_Shapes);

    vec3 normTest = a_Contact.m_v3Normal;
    float test2 = normTest.dot(v3LightDirection);

    // No shadow
    if (!test) {
        a_ResultColor += lightColor * !test * test2;
    }
    else {
        a_ResultColor = Color(); // Test code - change color to black.
    }
}

Answer 1

You have several bugs:

• in Sphere::Collides, m_fCollisionTime is not set, when t2>=t1
• in Sphere::Collides, if m_fCollisionTime is negative, then the ray actually doesn't intersect with the sphere (this causes the strange shadow on the top of the ball)
• put the plane lower, and you'll see the shadow of the ball
• you need to check for nearest collision, when shooting a ray from the eye (just try, swap the order of the objects, and the sphere suddenly becomes behind the plane)

With these fixed, you'll get this: