Light attributes in OpenGL ES 1.1

  • There is bug in the file TrainingCourse/06_IntroducingPOD/OGLES/OGLESIntroducingPOD.cpp in the Khronos OpenGL ES 1.1 SDKs (OGLES_WINDOWS_X86EMULATION_2.08.28.0634, the download file is OGLES_WINDOWS_X86EMULATION_2.08.28.0634.msi):

    (from line 432 to line 444):
    == BEIGN ==
    m_Scene.GetLight(vPos, *(PVRTVec3*)&vLightDirection, 0);
    // Specify the light direction in world space
    glLightfv(GL_LIGHT0, GL_POSITION, (float*)&vLightDirection);
  • We can get light attribute about the position, direction from POD file with class CPVRTModelPOD, how about others like type(point, spot, direct), angle & exponent for spot? Thanks.

I think I got the answer about the second point(how about the attributes of light) – we can get the attributes from the class SPODLight, normally we access the lights from POD from the array pLight in class CPVRTModelPOD.

Hi Yiwen.

The issue which you describe isn’t actually a bug. To specify a directional light in OpenGL you pass in a directional vector with the w component set to 0 to glLightfv with the enum GL_POSITION. As per OpenGL documentation:

"If the w component of the position is 0, the light is treated as a directional source. Diffuse and specular lighting calculations take the light’s direction, but not its actual position, into account, and attenuation is disabled."

If you take a look at the code again you’ll see the line …


vLightDirection.w = 0;

... before the call to glLightfv.


            Arron2011-08-31 12:22:05

Hi Arron:

  I see now – the codes in SDK are for the directional light(w = 0.0). If we want to setup attributes for other types such as point light or spot light, we have to put the variable “vPos” as the parameter(w = 1.0 to point out that is position vector) for GL_POSITION.

That it exactly right, yes. Point lights need only GL_POSITION to be set (with w component = 1.0) and spot lights require GL_POSITION (with the previous requirements) and GL_SPOT_DIRECTION with a directional vector. Of course spot lights have more parameters too (such as exponent and cutoff) but these are the enums associated with position and direction.

Best regards.

Arron, late thanks Smile