import 'dart:html';
import 'dart:web_gl';
import 'dart:typed_data';

void main() {
  CanvasElement canvas = querySelector('#game_canvas');
  RenderingContext gl = canvas.getContext('experimental-webgl');

  /*======== Defining and storing the geometry ===========*/

  Float32List vertices = Float32List.fromList([
    -0.5,
    0.5,
    0.0,
    -0.5,
    -0.5,
    0.0,
    0.5,
    -0.5,
    0.0,
  ]);

  Uint32List indices = Uint32List.fromList([0, 1, 2]);

  // Create an empty buffer object to store vertex buffer
  var vertex_buffer = gl.createBuffer();

  // Bind appropriate array buffer to it
  gl.bindBuffer(WebGL.ARRAY_BUFFER, vertex_buffer);

  // Pass the vertex data to the buffer
  gl.bufferData(WebGL.ARRAY_BUFFER, vertices, WebGL.STATIC_DRAW);

  // Unbind the buffer
  gl.bindBuffer(WebGL.ARRAY_BUFFER, null);

  // Create an empty buffer object to store Index buffer
  var Index_Buffer = gl.createBuffer();

  // Bind appropriate array buffer to it
  gl.bindBuffer(WebGL.ELEMENT_ARRAY_BUFFER, Index_Buffer);

  // Pass the vertex data to the buffer
  gl.bufferData(
      WebGL.ELEMENT_ARRAY_BUFFER, indices, WebGL.STATIC_DRAW);

  // Unbind the buffer
  gl.bindBuffer(WebGL.ELEMENT_ARRAY_BUFFER, null);

  /*================ Shaders ====================*/

  // Vertex shader source code
  var vertCode = 'attribute vec3 coordinates;' +
      'void main(void) {' +
      ' gl_Position = vec4(coordinates, 1.0);' +
      '}';

  // Create a vertex shader object
  var vertShader = gl.createShader(WebGL.VERTEX_SHADER);

  // Attach vertex shader source code
  gl.shaderSource(vertShader, vertCode);

  // Compile the vertex shader
  gl.compileShader(vertShader);

  //fragment shader source code
  var fragCode =
      'void main(void) {' + ' gl_FragColor = vec4(0.0, 0.0, 0.0, 0.1);' + '}';

  // Create fragment shader object
  var fragShader = gl.createShader(WebGL.FRAGMENT_SHADER);

  // Attach fragment shader source code
  gl.shaderSource(fragShader, fragCode);

  // Compile the fragmentt shader
  gl.compileShader(fragShader);

  // Create a shader program object to store
  // the combined shader program
  var shaderProgram = gl.createProgram();

  // Attach a vertex shader
  gl.attachShader(shaderProgram, vertShader);

  // Attach a fragment shader
  gl.attachShader(shaderProgram, fragShader);

  // Link both the programs
  gl.linkProgram(shaderProgram);

  // Use the combined shader program object
  gl.useProgram(shaderProgram);

  /*======= Associating shaders to buffer objects =======*/

  // Bind vertex buffer object
  gl.bindBuffer(WebGL.ARRAY_BUFFER, vertex_buffer);

  // Bind index buffer object
  gl.bindBuffer(WebGL.ELEMENT_ARRAY_BUFFER, Index_Buffer);

  // Get the attribute location
  var coord = gl.getAttribLocation(shaderProgram, "coordinates");

  // Point an attribute to the currently bound VBO
  gl.vertexAttribPointer(coord, 3, WebGL.FLOAT, false, 0, 0);

  // Enable the attribute
  gl.enableVertexAttribArray(coord);

  /*=========Drawing the triangle===========*/

  // Clear the canvas
  gl.clearColor(0.5, 0.5, 0.5, 0.9);

  // Enable the depth test
  gl.enable(WebGL.DEPTH_TEST);

  // Clear the color buffer bit
  gl.clear(WebGL.COLOR_BUFFER_BIT);

  // Set the view port
  gl.viewport(0, 0, canvas.width, canvas.height);

  // Draw the triangle
  gl.drawElements(WebGL.TRIANGLES, indices.length, WebGL.UNSIGNED_SHORT, 0);
}