Triangle

From: https://www.cs.unm.edu/~angel/WebGL/7E/CLASS/triangle.html

by asterix77

HTML

<!DOCTYPE html>
<html>

  <head>
    <script id="vertex-shader" type="x-shader/x-vertex">
    attribute vec4 vPosition;
		attribute vec4 vColor;
		varying vec4 fColor;
		void main()
		{
			gl_Position = vPosition;
			fColor = vColor;
		}
		</script>
    <script id="fragment-shader" type="x-shader/x-fragment">
		precision mediump float;
		varying vec4 fColor;
		void main()
		{
			gl_FragColor = fColor;
		}
    </script>
    <script type="text/javascript" src="https://www.cs.unm.edu/~angel/WebGL/7E/Common/webgl-utils.js"></script>
    <script type="text/javascript" src="https://www.cs.unm.edu/~angel/WebGL/7E/Common/initShaders.js"></script>
    <script type="text/javascript" src="https://www.cs.unm.edu/~angel/WebGL/7E/Common/MV.js"></script>
  </head>

  <body>
    <canvas id="gl-canvas" width="256" height="256">
Oops ... your browser doesn't support the HTML5 canvas element
</canvas>
  </body>

</html>

JavaScript

var gl;
var points;


function init() {
  var canvas = document.getElementById("gl-canvas");
  gl = WebGLUtils.setupWebGL(canvas);
  if (!gl) {
    alert("WebGL isn't available");
  }

  // Three Vertices 
  var vertices = [
    vec2(-1, -1),
    vec2(0, 1),
    vec2(1, -1)
  ];
  
  var colors = [
  	vec3(1, 0, 0),
    vec3(0, 1, 0),
    vec3(1, 1, 0)
  ];


  //  Configure WebGL
  gl.viewport(0, 0, canvas.width, canvas.height);
  gl.clearColor(1.0, 1.0, 1.0, 1.0);

  //  Load shaders and initialize attribute buffers
  var program = initShaders(gl, "vertex-shader", "fragment-shader");
  gl.useProgram(program);

  // Load the data into the GPU
  var bufferId = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, bufferId);
  gl.bufferData(gl.ARRAY_BUFFER, flatten(vertices), gl.STATIC_DRAW);

  // Associate out shader variables with our data buffer
  var vPosition = gl.getAttribLocation(program, "vPosition");
  gl.vertexAttribPointer(vPosition, 2, gl.FLOAT, false, 0, 0);
  gl.enableVertexAttribArray(vPosition);
  
  var cBuffer = gl.createBuffer();
  gl.bindBuffer( gl.ARRAY_BUFFER, cBuffer );
  gl.bufferData( gl.ARRAY_BUFFER,   flatten(colors), gl.STATIC_DRAW );

  var vColor = gl.getAttribLocation( program, "vColor" );
  gl.vertexAttribPointer( vColor, 3, gl.FLOAT, false, 0, 0 );
  gl.enableVertexAttribArray( vColor );  
  
  render();
};

function render() {
  gl.clear(gl.COLOR_BUFFER_BIT);
  gl.drawArrays(gl.TRIANGLES, 0, 3);
}

init();