Culling faces

OpenGL Development
#1

So I’m debating this right now. Should I let OpenGL let its magic choose what face to cull, or should I use the normal to calculate if a face should be drawn.

Vertex Shader:


	out bool shouldDraw;
	
	void main(void) {
		vec3 fdx = dFdx(pass_position);
		vec3 fdy = dFdy(pass_position);
		vec3 faceNormal = normalize(cross(fdx,fdy));
		shouldDraw = dot(pass_surfaceNormal, faceNormal) > 0.0 // backface
	}

and discard; any pixels with shouldDraw be to true

or


GL11.glEnable(GL11.GL_CULL_FACE);
GL11.glCulLFace(GL11.GL_BACK);

I find it awarding doing the first one because you can control cull settings in the shader when you have a transparent object. But there might be this large overhead due to me not knowing if OpenGL does some per-frame lengthy determination which might be true because of how it renders.