<!doctype html>
<html>
<body>
<canvas width = "300" height = "300" id = "my_Canvas"></canvas>
<script>
/* Step1: Prepare the canvas and get WebGL context */
var canvas = document.getElementById('my_Canvas');
var gl = canvas.getContext('experimental-webgl');
/* Step2: Define the geometry and store it in buffer objects */
var vertices = [-0.5, 0.5, -0.5, -0.5, 0.0, -0.5,];
// Create a new buffer object
var vertex_buffer = gl.createBuffer();
// Bind an empty array buffer to it
gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);
// Pass the vertices data to the buffer
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
// Unbind the buffer
gl.bindBuffer(gl.ARRAY_BUFFER, null);
/* Step3: Create and compile Shader programs */
// Vertex shader source code
var vertCode =
'attribute vec2 coordinates;' +
'void main(void) {' + ' gl_Position = vec4(coordinates,0.0, 1.0);' + '}';
//Create a vertex shader object
var vertShader = gl.createShader(gl.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(gl.FRAGMENT_SHADER);
// Attach fragment shader source code
gl.shaderSource(fragShader, fragCode);
// Compile the fragment shader
gl.compileShader(fragShader);
// Create a shader program object to store 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 programs
gl.linkProgram(shaderProgram);
// Use the combined shader program object
gl.useProgram(shaderProgram);
/* Step 4: Associate the shader programs to buffer objects */
//Bind vertex buffer object
gl.bindBuffer(gl.ARRAY_BUFFER, vertex_buffer);
//Get the attribute location
var coord = gl.getAttribLocation(shaderProgram, "coordinates");
//point an attribute to the currently bound VBO
gl.vertexAttribPointer(coord, 2, gl.FLOAT, false, 0, 0);
//Enable the attribute
gl.enableVertexAttribArray(coord);
/* Step5: Drawing the required object (triangle) */
// Clear the canvas
gl.clearColor(0.5, 0.5, 0.5, 0.9);
// Enable the depth test
gl.enable(gl.DEPTH_TEST);
// Clear the color buffer bit
gl.clear(gl.COLOR_BUFFER_BIT);
// Set the view port
gl.viewport(0,0,canvas.width,canvas.height);
// Draw the triangle
gl.drawArrays(gl.TRIANGLES, 0, 3);
</script>
</body>
</html>
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