Drawing a Polygon

This JavaScript WebGL program demonstrates how draw a simple polygon using a triangle fan.

DrawPolygon.html

<!DOCTYPE html>
<html>
  <head>
    <title>XoaX.net's WebGL</title>
    <script  id="idVertexShader" type="c">
      attribute vec2 qCoordXY;

      void main() {
        gl_Position = vec4(qCoordXY, 0.0, 1.0);
      }
    </script>

    <script  id="idFragmantShader" type="c">
      void main() {
        gl_FragColor = vec4(0.5, 0.3, 0.3, 1.0);
      }
    </script>

    <script type="text/javascript">
    var gqGL = null;
    var gqProgram = null;
    function CreateProgramAndContext() {
      // Get the WebGL Context
      var qCanvas = document.querySelector("#idCanvas");
      gqGL = qCanvas.getContext("webgl");

      // Compile the vertex shader
      var sVertexShaderCode = document.querySelector("#idVertexShader").text;
      var qVertexShader = gqGL.createShader(gqGL.VERTEX_SHADER);
      gqGL.shaderSource(qVertexShader, sVertexShaderCode);
      gqGL.compileShader(qVertexShader);

      // Compile the fragment shader
      var sFragmentShaderCode = document.querySelector("#idFragmantShader").text;
      var qFragmentShader = gqGL.createShader(gqGL.FRAGMENT_SHADER);
      gqGL.shaderSource(qFragmentShader, sFragmentShaderCode);
      gqGL.compileShader(qFragmentShader);

      // Compile and link the program
      gqProgram = gqGL.createProgram();
      gqGL.attachShader(gqProgram, qVertexShader);
      gqGL.attachShader(gqProgram, qFragmentShader);
      gqGL.linkProgram(gqProgram);
      gqGL.useProgram(gqProgram);
    }

    function Initialization() {
      CreateProgramAndContext();
      var faVertices = [0.0, 0.46, 0.55, 0.1, 0.32, -0.41, -0.32, -0.41, -0.55, 0.1];
      var iVerticesBuffer = gqGL.createBuffer();
      gqGL.bindBuffer(gqGL.ARRAY_BUFFER, iVerticesBuffer);
      gqGL.bufferData(gqGL.ARRAY_BUFFER, new Float32Array(faVertices), gqGL.STATIC_DRAW);

      var iCoordXY = gqGL.getAttribLocation(gqProgram, "qCoordXY");
      gqGL.vertexAttribPointer(iCoordXY, 2, gqGL.FLOAT, false, 0, 0);
      gqGL.enableVertexAttribArray(iCoordXY);

      gqGL.clearColor(0.5, 0.5, 0.3, 1.0);
      gqGL.enable(gqGL.DEPTH_TEST);
      gqGL.clear(gqGL.COLOR_BUFFER_BIT);
      gqGL.drawArrays(gqGL.TRIANGLE_FAN, 0, 5);
    }
    </script>
  </head>
  <body onload="Initialization()">
    <canvas id="idCanvas" width="400", height="400" style="border:1px solid lightgray"></canvas>
  </body>
</html>

WebGL JavaScript

Drawing a Polygon

DrawPolygon.html

Output