OpenGL ES 1.1: Culling versus near clip plane -- performance

Question

I'm writing an app in OpenGL ES 1.1. I'm rendering a textured sphere around the viewer, i.e. the eye viewpoint is in the centre of the sphere. Because I don't need any lighting effects, there's no need at present to have surface normals for each vertex. However, I'd need those to turn on backface culling. Is there any benefit in turning on backface culling though? Because my eye is at the centre of the sphere, any faces that got culled (i.e. behind the eye) would be dealt with by the near z plane clipping anyway. So would adding surface normals and turning on backface culling get me any performance benefit, in this situation? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

First of all, surface normals don't have anything to do with back-face culling, at least for OpenGL's part. The front or back-sidedness of a face is determined by the ordering of its vertices when projected into screen space, which by default (which can be changed using glFrontFace) is front-facing when the vertices are ordered counter-clockwise and back-facing when ordered clockwise. So you don't need any normals. These are only used for lighting computation and nothing else. How should the normal of a single vertex influence the surrounding faces orientation? Take the average of the vertex normals? What if these are completely opposite or something more weird (since the user can specify any normals he wants)? That said you also don't need back-face culling for your sphere, since from the inside you always see the front-side anyway. But it also doesn't hurt to turn it on, since you also don't see any back-faces (and you can assume face-culling to be for free). But in this case pay attention to the orientation or your faces, it may be that you need to enable front-face culling (glCullFace(GL_FRONT)) instead of back-face culling when you are in the inside of the sphere, since most objects are tessellated to have their triangles facing outside. Or you could just switch to glFrontFace(GL_CW).