Question

I’m trying to read some OpenGL tutorials on the net. the problem is that I found some old ones that use gluPerspective(). gluPerspective was deprecated in OpenGL 3.0 and removed in 3.1.

What function can I use instead?

I’m using C++ with latest FreeGlut installed.

Answer 1

You have to compute the matrix manually and then pass it to OpenGL.

Computing the matrix

This snippet of code is based on the gluPerspective documentation.

 void BuildPerspProjMat(float *m, float fov, float aspect,
 float znear, float zfar)
 {
  float f = 1/tan(fov * PI_OVER_360);

  m[0]  = f/aspect;
  m[1]  = 0;
  m[2]  = 0;
  m[3]  = 0;

  m[4]  = 0;
  m[5]  = f;
  m[6]  = 0;
  m[7]  = 0;

  m[8]  = 0;
  m[9]  = 0;
  m[10] = (zfar + znear) / (znear - zfar);
  m[11] = -1;

  m[12] = 0;
  m[13] = 0;
  m[14] = 2*zfar*znear / (znear - zfar);
  m[15] = 0;
 }

There is a C++ library called OpenGL Mathematics that may be useful.

Loading the Matrix in OpenGL 3.1

I am still new to the OpenGL 3.1 API, but you need to update a matrix on the GPU and then make use of it in your vertex shader to get the proper perspective. The following code just loads the matrix using glUniformMatrix4fv onto the video card.

{
  glUseProgram(shaderId);
  glUniformMatrix4fv(glGetUniformLocation(shaderId, "u_proj_matrix"),
                     1, GL_FALSE, theProjectionMatrix);
  RenderObject();
  glUseProgram(0);
}

A simple vertex shader from a random blog (found through stack overflow).

attribute vec4      a_position;
attribute vec4      a_color;

varying vec4        v_color;

uniform mat4 u_proj_matrix;
uniform mat4 u_model_matrix;

void main() {
  mat4 mvp_matrix = u_proj_matrix * u_model_matrix;
  v_color = a_color;
  gl_Position = mvp_matrix * a_position;
}