How to use the gl-matrix-mat4.perspective function in gl-matrix-mat4

function render() {
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
  gl.enable(gl.DEPTH_TEST);
  clear();


  characterPos = [0, 0, 0];
  shader.bind();

  shader.uniforms.unitsPerEm = unitsPerEm;
  shader.uniforms.model = mat4.identity(m4scratch);
  shader.uniforms.projection = mat4.perspective(
    m4scratch,
    Math.PI/4,
    gl.canvas.width/gl.canvas.height,
    0.1,
    1000.00
  );

  shader.uniforms.view = camera.view(m4scratch);
  var now = Date.now();

  letters.forEach(function(letter) {
    letter.geometry.bind(shader);
    shader.uniforms.characterPos = characterPos;
    shader.uniforms.time = now - start;
    letter.geometry.draw(gl.TRIANGLES);
    letter.geometry.bind(shader);