(*
  This code comes from:
    http://gpwiki.org/index.php/OpenGL:Codes:Simple_GLSL_example
  which is under GNU::FDL license
  (ported to OCaml/glMLite by Florent Monnier)
*)
open GL
open Glu
open Glut

let waveTime = ref 0.0
let waveWidth = ref 0.1
let waveHeight = ref 3.0
let waveFreq = ref 0.1

let waveTimeLoc = ref 0
let waveWidthLoc = ref 0
let waveHeightLoc = ref 0


let ( += ) a b =
  a := !a +. b;
;;

let ( -= ) a b =
  a := !a -. b;
;;


let display() = 
  glClear [GL_COLOR_BUFFER_BIT];
  glLoadIdentity();
 
  glTranslate 0.0 0.0 (-150.0);
  glRotate (-45.0) 1.0 0.0 0.0;
 
  (* Change time *)
  glUniform1f !waveTimeLoc !waveTime;
  glUniform1f !waveWidthLoc !waveWidth;
  glUniform1f !waveHeightLoc !waveHeight;
 
  (* Draw here a plain surface *)
  glBegin GL_QUADS;
  for i = -50 to pred 50 do
    for j = -50 to pred 50 do
      let glVertex2i a b = glVertex2 (float a) (float b) in
      glVertex2i i j;
      glVertex2i (i + 1) j;
      glVertex2i (i + 1) (j + 1);
      glVertex2i i (j + 1);
    done;
  done;
  glEnd();
 
  waveTime += !waveFreq;
 
  glFlush();
  glutSwapBuffers();
  glutPostRedisplay();
;;


let setShaders() =
  (* The vertex shader *)
  let vsSource = "
/* Vertex shader */
uniform float waveTime;
uniform float waveWidth;
uniform float waveHeight;
 
void main(void)
{
        vec4 v = vec4(gl_Vertex);
        
        v.z = sin(waveWidth * v.x + waveTime) * cos(waveWidth * v.y + waveTime) * waveHeight;
        
        gl_Position = gl_ModelViewProjectionMatrix * v;
}
  " in
  let fsSource = "
/* Vertex shader */
uniform float waveTime;
uniform float waveWidth;
uniform float waveHeight;
 
void main(void)
{
        vec4 v = vec4(gl_Vertex);
        
        v.z = sin(waveWidth * v.x + waveTime) * cos(waveWidth * v.y + waveTime) * waveHeight;
        
        gl_Position = gl_ModelViewProjectionMatrix * v;
}
  " in
 
  (* Compile and load the program *)
 
  let vs = glCreateShader GL_VERTEX_SHADER in
  glShaderSource vs vsSource;
  glCompileShader vs;
  print_string(glGetShaderInfoLog vs);
 
  let fs = glCreateShader GL_FRAGMENT_SHADER in
  glShaderSource fs fsSource;
  glCompileShader fs;
  print_string(glGetShaderInfoLog fs);
 
  let sp = glCreateProgram() in
  glAttachShader sp vs;
  glAttachShader sp fs;
  glLinkProgram sp;
  print_string(glGetProgramInfoLog sp);
 
  glUseProgram sp;

  waveTimeLoc := glGetUniformLocation sp "waveTime";
  waveWidthLoc := glGetUniformLocation sp "waveWidth";
  waveHeightLoc := glGetUniformLocation sp "waveHeight";
  print_string(glGetProgramInfoLog sp);
 
  Printf.printf "wave parameters location: %d %d %d\n%!" !waveTimeLoc !waveWidthLoc !waveHeightLoc;
;;


let keyboard ~key ~x ~y =
  match key with
  | '\027' ->
      (*
      glDeleteShader vs;
      glDeleteShader fs;
      glDeleteProgram sp;
      *)
      exit(0)

  | '+' ->
      waveFreq += 0.1;
      Printf.printf "Modified time waveFreq + 0.1: %f\n%!" !waveFreq;
 
  | '-' ->
      waveFreq -= 0.1;
      Printf.printf "Modified time waveFreq - 0.1: %f\n%!" !waveFreq;
 
  | 'w' ->
      waveWidth += 0.1;
      Printf.printf "Modified width waveWidth + 0.1: %f\n%!" !waveWidth;
 
  | 'q' ->
      waveWidth -= 0.1;
      Printf.printf "Modified width waveWidth - 0.1: %f\n%!" !waveWidth;
 
  | 'h' ->
      waveHeight += 0.1;
      Printf.printf "Modified width waveWidth + 0.1: %f\n%!" !waveHeight;
 
  | 'g' ->
      waveHeight -= 0.1;
      Printf.printf "Modified width waveWidth - 0.1: %f\n%!" !waveHeight;

  | _ -> ()
;;


let reshape ~width ~height =
  glViewport 0 0 width height;
  glMatrixMode GL_PROJECTION;
  glLoadIdentity();
  gluPerspective 40. 1. 0.0001 1000.0;
  glMatrixMode GL_MODELVIEW;
  glutPostRedisplay();
;;


let init_gl ~width ~height =
  glShadeModel GL_SMOOTH;
  glViewport 0 0 width height;
 
  glMatrixMode GL_PROJECTION;
  glLoadIdentity();
  gluPerspective 40. 1. 0.0001 1000.0;
  glMatrixMode GL_MODELVIEW;
 
  glPolygonMode GL_FRONT_AND_BACK GL_LINE;
;;


let () =
  ignore(glutInit Sys.argv);
  let width, height = 400, 400 in

  glutInitDisplayMode[GLUT_RGBA; GLUT_DOUBLE; GLUT_DEPTH];
  glutInitWindowPosition ~x:100 ~y:100;
  glutInitWindowSize ~width ~height;

  ignore(glutCreateWindow ~title:"GLSL demo");

  (* init openGL *)
  glEnable GL_DEPTH_TEST;

  setShaders();
  init_gl ~width ~height;

  (* callback functions *)
  glutDisplayFunc ~display;
  glutKeyboardFunc ~keyboard;
  (*
  glutReshapeFunc ~reshape;
  *)

  (* enter the main loop *)
  glutMainLoop();
;;