Draw a Line Segment

This JavaScript program demonstrates how to draw a line segment in a WebGL program.

DrawALineSegment.html

<!DOCTYPE html>
<html>
  <head>
    <title>XoaX.net's WebGL</title>

    <script  id="idVertexShader" type="c">
      // The attribute receives data from the buffer
      attribute vec2 afEndPoints;

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

    <script  id="idFragmantShader" type="c">
      precision mediump float;

      void main() {
        gl_FragColor = vec4(.5, 1, 1, 1);
      }
    </script>

    <script type="text/javascript">
    function Render() {
      // Get the WebGL Context
      var qCanvas = document.querySelector("#idCanvasWebGL");
      var qGL = qCanvas.getContext("webgl");

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

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

      // Compile and link the program
      var qProgram = qGL.createProgram();
      qGL.attachShader(qProgram, qVertexShader);
      qGL.attachShader(qProgram, qFragmentShader);
      qGL.linkProgram(qProgram);

      // Set up the buffer for the endpoints
      var qEndpointAttributeLocation = qGL.getAttribLocation(qProgram, "afEndPoints");
      var qEndpointBuffer = qGL.createBuffer();
      qGL.bindBuffer(qGL.ARRAY_BUFFER, qEndpointBuffer);
      qGL.bufferData(qGL.ARRAY_BUFFER, new Float32Array([ -.5, -.8, .7, .8]), qGL.STATIC_DRAW);
      qGL.enableVertexAttribArray(qEndpointAttributeLocation);
      qGL.vertexAttribPointer(qEndpointAttributeLocation, 2, qGL.FLOAT, false, 0, 0);

      qGL.useProgram(qProgram);

      qGL.clearColor(0, 0.7, 0.8, 1.0);
      qGL.clear(qGL.COLOR_BUFFER_BIT);
      qGL.drawArrays(qGL.LINES, 0, 2);
    }
    </script>
  </head>
  <body onload="Render();">
    <canvas id="idCanvasWebGL" width="400", height="400" style="border:1px solid red"></canvas>
  </body>
</html>

WebGL JavaScript

Draw a Line Segment

DrawALineSegment.html

Output