shader.js

/**
 * Creates and compiles a shader.
 *
 * @param {!WebGLRenderingContext} gl The WebGL Context.
 * @param {string} shaderSource The GLSL source code for the shader.
 * @param {number} shaderType The type of shader, VERTEX_SHADER or
 *     FRAGMENT_SHADER.
 * @return {!WebGLShader} The shader.
 */
function compileShader(gl, shaderSource, shaderType) {
  // Create the shader object
  var shader = gl.createShader(shaderType);
 
  // Set the shader source code.
  gl.shaderSource(shader, shaderSource);
 
  // Compile the shader
  gl.compileShader(shader);
 
  // Check if it compiled
  var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
  if (!success) {
    // Something went wrong during compilation; get the error
    throw "could not compile shader:" + gl.getShaderInfoLog(shader);
  }
 
  return shader;
}


/**
 * Creates a shader from the content of a script tag.
 *
 * @param {!WebGLRenderingContext} gl The WebGL Context.
 * @param {string} scriptId The id of the script tag.
 * @param {string} opt_shaderType. The type of shader to create.
 *     If not passed in will use the type attribute from the
 *     script tag.
 * @return {!WebGLShader} A shader.
 */
function createShaderFromScript(gl, scriptId, opt_shaderType) {
  // look up the script tag by id.
  var shaderScript = document.getElementById(scriptId);
  if (!shaderScript) {
    throw("*** Error: unknown script element" + scriptId);
  }
 
  // extract the contents of the script tag.
  var shaderSource = shaderScript.text;
 
  // If we didn't pass in a type, use the 'type' from
  // the script tag.
  if (!opt_shaderType) {
    if (shaderScript.type == "x-shader/x-vertex") {
      opt_shaderType = gl.VERTEX_SHADER;
    } else if (shaderScript.type == "x-shader/x-fragment") {
      opt_shaderType = gl.FRAGMENT_SHADER;
    } else if (!opt_shaderType) {
      throw("*** Error: shader type not set");
    }
  }
 
  return compileShader(gl, shaderSource, opt_shaderType);
};

/**
 * Creates a program from 2 shaders.
 *
 * @param {!WebGLRenderingContext) gl The WebGL context.
 * @param {!WebGLShader} vertexShader A vertex shader.
 * @param {!WebGLShader} fragmentShader A fragment shader.
 * @return {!WebGLProgram} A program.
 */
function createProgram(gl, vertexShader, fragmentShader) {
  // create a program.
  var program = gl.createProgram();
 
  // attach the shaders.
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
 
  // link the program.
  gl.linkProgram(program);
 
  // Check if it linked.
  var success = gl.getProgramParameter(program, gl.LINK_STATUS);
  if (!success) {
      // something went wrong with the link
      throw ("program filed to link:" + gl.getProgramInfoLog (program));
  }
 
  return program;
};

/**
 * Creates a program from 2 script tags.
 *
 * @param {!WebGLRenderingContext} gl The WebGL Context.
 * @param {string} vertexShaderId The id of the vertex shader script tag.
 * @param {string} fragmentShaderId The id of the fragment shader script tag.
 * @return {!WebGLProgram} A program
 */
function createProgramFromScripts(
    gl, vertexShaderId, fragmentShaderId) {
  var vertexShader = createShaderFromScriptTag(gl, vertexShaderId, gl.VERTEX_SHADER);
  var fragmentShader = createShaderFromScriptTag(gl, fragmentShaderId, gl.FRAGMENT_SHADER);
  return createProgram(gl, vertexShader, fragmentShader);
}