/*
 * Copyright 2018 The Emscripten Authors.  All rights reserved.
 * Emscripten is available under two separate licenses, the MIT license and the
 * University of Illinois/NCSA Open Source License.  Both these licenses can be
 * found in the LICENSE file.
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <emscripten/emscripten.h>
#include <emscripten/html5.h>
#include <GLES3/gl3.h>

GLuint compile_shader(GLenum shaderType, const char *src)
{
  GLuint shader = glCreateShader(shaderType);
  glShaderSource(shader, 1, &src, NULL);
  glCompileShader(shader);

  GLint isCompiled = 0;
  glGetShaderiv(shader, GL_COMPILE_STATUS, &isCompiled);
  if (!isCompiled)
  {
    GLint maxLength = 0;
    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &maxLength);
    char *buf = (char*)malloc(maxLength+1);
    glGetShaderInfoLog(shader, maxLength, &maxLength, buf);
    printf("%s\n", buf);
    free(buf);
    return 0;
  }

   return shader;
}

GLuint create_program(GLuint vertexShader, GLuint fragmentShader)
{
   GLuint program = glCreateProgram();
   glAttachShader(program, vertexShader);
   glAttachShader(program, fragmentShader);
   glBindAttribLocation(program, 0, "apos");
   glBindAttribLocation(program, 1, "acolor");
   glLinkProgram(program);
   return program;
}

int main()
{
  EmscriptenWebGLContextAttributes attr;
  emscripten_webgl_init_context_attributes(&attr);
#ifdef EXPLICIT_SWAP
  attr.explicitSwapControl = 1;
#endif
  attr.majorVersion = 2;
  EMSCRIPTEN_WEBGL_CONTEXT_HANDLE ctx = emscripten_webgl_create_context("#canvas", &attr);
  assert(ctx && "Failed to create WebGL2 context");
  emscripten_webgl_make_context_current(ctx);

  static const char vertex_shader[] =
    "#version 100\n"
    "attribute vec4 apos;"
    "attribute vec4 acolor;"
    "varying vec4 color;"
    "void main() {"
      "color = acolor;"
      "gl_Position = apos;"
    "}";
  GLuint vs = compile_shader(GL_VERTEX_SHADER, vertex_shader);

  static const char fragment_shader[] =
    "#version 100\n"
    "precision lowp float;"
    "varying vec4 color;"
    "void main() {"
      "gl_FragColor = color;"
    "}";
  GLuint fs = compile_shader(GL_FRAGMENT_SHADER, fragment_shader);

  GLuint program = create_program(vs, fs);
  glUseProgram(program);

  static const uint32_t pos_and_color[] = {
  //  1,0,y,x,    a,b,g,r
    0x400b36cd, 0xc00003ff,
    0x400b3533, 0xc00ffc00,
    0x4004cc00, 0xfff00000,
  };

  GLuint vbo;
  glGenBuffers(1, &vbo);
  glBindBuffer(GL_ARRAY_BUFFER, vbo);
  glBufferData(GL_ARRAY_BUFFER, sizeof(pos_and_color), pos_and_color, GL_STATIC_DRAW);
  glVertexAttribPointer(0, 4, GL_INT_2_10_10_10_REV, GL_TRUE, 8, 0);
  assert(glGetError() == GL_NO_ERROR && "glVertexAttribPointer with GL_INT_2_10_10_10_REV failed");
  glVertexAttribPointer(1, 4, GL_UNSIGNED_INT_2_10_10_10_REV, GL_TRUE, 8, (void*)4);
  assert(glGetError() == GL_NO_ERROR && "glVertexAttribPointer with GL_UNSIGNED_INT_2_10_10_10_REV failed");

  glEnableVertexAttribArray(0);
  glEnableVertexAttribArray(1);

  glClearColor(0.3f,0.3f,0.3f,1);
  glClear(GL_COLOR_BUFFER_BIT);
  glDrawArrays(GL_TRIANGLES, 0, 3);

#ifdef EXPLICIT_SWAP
  emscripten_webgl_commit_frame();
#endif

  return 0;
}