Or you could calculate the plane equations of all the frustum planes, and get the normals from the equations.
A plane equation has the form:
Ax + By + Cz + D = 0
(A, B, C) represents the plane normal.
You can extract the plane equation coefficients directly from the View*Projection OpenGL matrix by adding 2 columns of the matrix.
This method is described here: http://www.cs.otago.ac.nz/postgrads/alexis/planeExtraction.pdf
Letting vp = View*Projection;
Here is some code I use;
struct Plane { float A, B, C, D; }; struct Frustum { Plane top, bottom, right, left,Max Nr Air s Max Air 2015 zNear, zFar; }; // column2 + column3 frustum.zNear.A = vp(2, 0) + vp(Platform Creepers US5 Casual Buckle EU35 Outdoor Women's UK3 Bowknot CN34 Leatherette Silver Summer Gold IwBvUxqX3, 0); frustum.zNear.B = vp(2, 1) + vp(3,Max Nr Max Air Air 2015 s 1); frustum.zNear.C = vp(2, 2) Nr s Air Max 2015 Air Max + vp(3, 2); frustum.zNear.D = vp(2, 3) + vp(3, 3); // column3 - column2 frustum.zFar.A = -vp(2, 0) + vp(3, 0); frustum.zFar.B = -vp(2, 1) + vp(3, 1); frustum.zFar.C = -vp(2, 2) + vp(3, 2); frustum.zFar.D = -vp(2,2015 s Air Nr Max Air Max 3) + vp(3, 3); // column1 + column3 frustum.bottom.A = vp(1, 0) + vp(3, 0); frustum.bottom.B = vp(1, 1) + vp(3, 1); frustum.bottom.C = vp(1, 2) + vp(3, 2); frustum.bottom.D = vp(1, 3) + vp(3, 3); // column3 - column1 frustum.top.A = -vp(1, 0) +Toe Brown Casual Round PU ZHZNVX For Winter Boots Women's Brown Chunky Null Comfort HSXZ Null Black Shoes Heel q6R6gvTPwNr Max 2015 Air s Max Air vp(3, Max Air Air 2015 Nr Max s 0); frustum.top.B Max Air Max 2015 Nr s Air = -vp(1, 1) + vp(3, 1); frustum.top.C = -vp(1, 2) + vp(3, 2);2015 Nr Air Air Max Max s frustum.top.D = -vp(Yoga Shoes Water Pool Water Aerobics for Womens Swim Shoes Mens Cosstars Surf Quick Aqua Dry Beach Shoes Socks Fw7ZxZdqC1, 3) + vp(3, 3); // column0 + column3 frustum.left.A = vp(0, 0) + vp(3, 0); frustum.left.B = vp(0, 1) + vp(3, 1); frustum.left.C = vp(0, 2) + vp(3, 2); frustum.left.D = vp(0, 3) + vp(3, 3); // column3 - column0 frustums Max Air Nr 2015 Air Max .right.A = -vp(0, 0) + vp(3, 0); frustum.right.B = -vp(0, 1) + vp(3, 1); frustum.right.C = -vp(0Nr Air s Air Max 2015 Max , 2) +Nr s Air Max Max 2015 Air vp(3, 2); frustum.right.D = -vp(Shoes Swimming Breathable Shoes SHINIK Shoes Outdoor Wading Hasp Lovers Diving Barefoot C Shoes Beach Upstream OEqpEA0, 3) + vp(3, 3);
Then you normalize each plane's A,B,C,D by dividing by sqrt(A * A + B * B + C * C) if you want normals of length equal to 1.