DalTXColtsFan

02-20-2004, 10:46 AM

Anyone ever experienced unpredictable results when using an OpenGL light that's perfectly perpendicular to a normal?

I'm rendering several rectangular prisms, and I have a light that I'm trying to simulate the sun and moon with like this:

float afAmbientLight[4];

if (m_fFactor >= 0.0f && m_fFactor <= 0.5f) {

//sun's out

afAmbientLight[0] = 0.1f + 0.9f * sin(3.14159 * m_fFactor * 2.0f);

afAmbientLight[1] = 0.1f + 0.9f * sin(3.14159 * m_fFactor * 2.0f);

afAmbientLight[2] = 0.1f + 0.9f * sin(3.14159 * m_fFactor * 2.0f);

afAmbientLight[3] = 1.0f; }

else {

//moon's out

afAmbientLight[0] = 0.1f + 0.1f * sin(3.14159 * (m_fFactor - 0.5f) * 2.0f);

afAmbientLight[1] = 0.1f + 0.1f * sin(3.14159 * (m_fFactor - 0.5f) * 2.0f);

afAmbientLight[2] = 0.1f + 0.1f * sin(3.14159 * (m_fFactor - 0.5f) * 2.0f);

afAmbientLight[3] = 1.0f;

} glLightModelfv(GL_LIGHT_MODEL_AMBIENT, afAmbientLight);

glLightf(GL_LIGHT0, GL_SPOT_EXPONENT, 1.0f);

glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 90.0f);

glLightf(GL_LIGHT0, GL_CONSTANT_ATTENUATION, 1.0f);

glLightf(GL_LIGHT0, GL_LINEAR_ATTENUATION, 0.0f);

glLightf(GL_LIGHT0, GL_QUADRATIC_ATTENUATION, 0.0f);

//I don't know why this works, but I have better luck

//getting the sun or moon effect I want if I let the

//global ambient take care of ambient and let the

//directional light take care of diffuse and specular

float fAmbient[4] = {0.0f, 0.0f, 0.0f, 0.0f};

glLightfv(GL_LIGHT0, GL_AMBIENT, fAmbient);

float fDifSpec[4];

if (m_fFactor >= 0.0f && m_fFactor <= 0.5f) {

fDifSpec[0] = 1.0f;

fDifSpec[1] = 1.0f;

fDifSpec[2] = 0.0f;

fDifSpec[3] = 1.0f;

}

else

{

fDifSpec[0] = 1.0f;

fDifSpec[1] = 1.0f;

fDifSpec[2] = 1.0f;

fDifSpec[3] = 1.0f;

}

glLightfv(GL_LIGHT0, GL_DIFFUSE, fDifSpec);

glLightfv(GL_LIGHT0, GL_SPECULAR, fDifSpec);

//for all practical purposes, a directional light

//shines in the direction opposite its position

//and spot direction is ignored float

fPosition[4];

if (m_fFactor >= 0.0f && m_fFactor <= 0.5f) {

fPosition[0] = (float)cos(m_fFactor * 2 * 3.14159);

fPosition[1] = (float)sin(m_fFactor * 2 * 3.14159);

fPosition[2] = 0.0f;

fPosition[3] = 0.0f; }

else

{

fPosition[0] = (float)cos((m_fFactor - 0.5f) * 2 * 3.14159);

fPosition[1] = (float)sin((m_fFactor - 0.5f) * 2 * 3.14159);

fPosition[2] = 0.0f;

fPosition[3] = 0.0f; }

glLightfv(GL_LIGHT0, GL_POSITION, fPosition);

The normals on the prism sides facing front and back are (0, 0, 1) and (0, 0, -1).

What I'm seeing is these two sides "flicker" - and they flicker at exactly the same time each "cycle". Are there certain angles that light up the surface?

[This message has been edited by DalTXColtsFan (edited 02-20-2004).]

I'm rendering several rectangular prisms, and I have a light that I'm trying to simulate the sun and moon with like this:

float afAmbientLight[4];

if (m_fFactor >= 0.0f && m_fFactor <= 0.5f) {

//sun's out

afAmbientLight[0] = 0.1f + 0.9f * sin(3.14159 * m_fFactor * 2.0f);

afAmbientLight[1] = 0.1f + 0.9f * sin(3.14159 * m_fFactor * 2.0f);

afAmbientLight[2] = 0.1f + 0.9f * sin(3.14159 * m_fFactor * 2.0f);

afAmbientLight[3] = 1.0f; }

else {

//moon's out

afAmbientLight[0] = 0.1f + 0.1f * sin(3.14159 * (m_fFactor - 0.5f) * 2.0f);

afAmbientLight[1] = 0.1f + 0.1f * sin(3.14159 * (m_fFactor - 0.5f) * 2.0f);

afAmbientLight[2] = 0.1f + 0.1f * sin(3.14159 * (m_fFactor - 0.5f) * 2.0f);

afAmbientLight[3] = 1.0f;

} glLightModelfv(GL_LIGHT_MODEL_AMBIENT, afAmbientLight);

glLightf(GL_LIGHT0, GL_SPOT_EXPONENT, 1.0f);

glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 90.0f);

glLightf(GL_LIGHT0, GL_CONSTANT_ATTENUATION, 1.0f);

glLightf(GL_LIGHT0, GL_LINEAR_ATTENUATION, 0.0f);

glLightf(GL_LIGHT0, GL_QUADRATIC_ATTENUATION, 0.0f);

//I don't know why this works, but I have better luck

//getting the sun or moon effect I want if I let the

//global ambient take care of ambient and let the

//directional light take care of diffuse and specular

float fAmbient[4] = {0.0f, 0.0f, 0.0f, 0.0f};

glLightfv(GL_LIGHT0, GL_AMBIENT, fAmbient);

float fDifSpec[4];

if (m_fFactor >= 0.0f && m_fFactor <= 0.5f) {

fDifSpec[0] = 1.0f;

fDifSpec[1] = 1.0f;

fDifSpec[2] = 0.0f;

fDifSpec[3] = 1.0f;

}

else

{

fDifSpec[0] = 1.0f;

fDifSpec[1] = 1.0f;

fDifSpec[2] = 1.0f;

fDifSpec[3] = 1.0f;

}

glLightfv(GL_LIGHT0, GL_DIFFUSE, fDifSpec);

glLightfv(GL_LIGHT0, GL_SPECULAR, fDifSpec);

//for all practical purposes, a directional light

//shines in the direction opposite its position

//and spot direction is ignored float

fPosition[4];

if (m_fFactor >= 0.0f && m_fFactor <= 0.5f) {

fPosition[0] = (float)cos(m_fFactor * 2 * 3.14159);

fPosition[1] = (float)sin(m_fFactor * 2 * 3.14159);

fPosition[2] = 0.0f;

fPosition[3] = 0.0f; }

else

{

fPosition[0] = (float)cos((m_fFactor - 0.5f) * 2 * 3.14159);

fPosition[1] = (float)sin((m_fFactor - 0.5f) * 2 * 3.14159);

fPosition[2] = 0.0f;

fPosition[3] = 0.0f; }

glLightfv(GL_LIGHT0, GL_POSITION, fPosition);

The normals on the prism sides facing front and back are (0, 0, 1) and (0, 0, -1).

What I'm seeing is these two sides "flicker" - and they flicker at exactly the same time each "cycle". Are there certain angles that light up the surface?

[This message has been edited by DalTXColtsFan (edited 02-20-2004).]