framebuffer.js Example File

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  ** This file is part of the QtCanvas3D module of the Qt Toolkit.
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  Qt.include("gl-matrix.js")

  //
  // Draws a cube that has the Qt logo as decal texture on each face in to a texture.
  // That texture is used as the texture for drawing another cube on the screen.
  //

  var gl;

  var rttFramebuffer;
  var rttTexture;
  var rttWidth = 512;
  var rttHeight = 512;

  var cubeTexture = 0;

  var vertexPositionAttribute;
  var textureCoordAttribute;
  var vertexNormalAttribute;
  var vertexColorAttribute;
  var mvMatrix = mat4.create();
  var pMatrix  = mat4.create();
  var nMatrix  = mat4.create();
  var pMatrixUniform;
  var mvMatrixUniform;
  var nUniform;

  var canvas3d;
  var isLogEnabled = false;

  function log(message) {
      if (isLogEnabled)
          console.log(message)
  }

  function initializeGL(canvas, textureLoader) {
      canvas3d = canvas
      try {
          // Get the OpenGL context object that represents the API we call
          gl = canvas.getContext("canvas3d", {depth:true, antialias:true, alpha:false});

          // Setup the OpenGL state
          gl.enable(gl.DEPTH_TEST);
          gl.enable(gl.CULL_FACE);
          gl.cullFace(gl.BACK);
          gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);

          // Initialize the shader program
          initShaders();

          // Initialize vertex and color buffers
          initBuffers();

          // Load the Qt logo as texture
          var qtLogoImage = TextureImageFactory.newTexImage();
          qtLogoImage.imageLoaded.connect(function() {
              cubeTexture = gl.createTexture();
              cubeTexture.name = "CubeTexture";
              gl.bindTexture(gl.TEXTURE_2D, cubeTexture);
              gl.texImage2D(gl.TEXTURE_2D,    // target
                            0,                // level
                            gl.RGBA,          // internalformat
                            gl.RGBA,          // format
                            gl.UNSIGNED_BYTE, // type
                            qtLogoImage);    // pixels

              gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
              gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);
              gl.generateMipmap(gl.TEXTURE_2D);
          });
          qtLogoImage.imageLoadingFailed.connect(function() {
              console.log("Texture load FAILED, "+qtLogoImage.errorString);
          });
          qtLogoImage.src = "qrc:/qtlogo.png";

          // Create the framebuffer object
          rttFramebuffer = gl.createFramebuffer();
          rttFramebuffer.name = "OffscreenRenderTarget";
          gl.bindFramebuffer(gl.FRAMEBUFFER, rttFramebuffer);

          // Create the texture
          rttTexture = gl.createTexture();
          rttTexture.name = "OffscreenRenderTargetTexture";
          gl.bindTexture(gl.TEXTURE_2D, rttTexture);
          gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
          gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);
          gl.texImage2D(gl.TEXTURE_2D, 0,
                        gl.RGBA, rttWidth, rttHeight,
                        0, gl.RGBA, gl.UNSIGNED_BYTE,
                        null);
          gl.generateMipmap(gl.TEXTURE_2D);

          // Bind the texture as color attachment, create and bind a depth buffer
          gl.framebufferTexture2D(gl.FRAMEBUFFER,
                                  gl.COLOR_ATTACHMENT0,
                                  gl.TEXTURE_2D, rttTexture, 0);
          var renderbuffer = gl.createRenderbuffer();
          gl.bindRenderbuffer(gl.RENDERBUFFER, renderbuffer);
          gl.renderbufferStorage(gl.RENDERBUFFER,
                                 gl.DEPTH_COMPONENT16,
                                 rttWidth, rttHeight);
          gl.framebufferRenderbuffer(gl.FRAMEBUFFER,
                                     gl.DEPTH_ATTACHMENT,
                                     gl.RENDERBUFFER, renderbuffer);
          gl.bindTexture(gl.TEXTURE_2D, 0);
          gl.bindRenderbuffer(gl.RENDERBUFFER, 0);
          gl.bindFramebuffer(gl.FRAMEBUFFER, 0);
      } catch(e) {
          console.log("initializeGL FAILURE!");
          console.log(""+e);
          console.log(""+e.message);
      }
  }

  function degToRad(degrees) {
      return degrees * Math.PI / 180;
  }

  function paintGL(canvas) {
      // bind the FBO and setup viewport
      gl.bindFramebuffer(gl.FRAMEBUFFER, rttFramebuffer);
      gl.viewport(0, 0, rttWidth, rttHeight);

      gl.clearColor(0.95, 0.95, 0.95, 1.0);
      gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

      // Bind the loaded texture
      gl.bindTexture(gl.TEXTURE_2D, cubeTexture);

      // Calculate and set matrix uniforms
      mat4.perspective(pMatrix, degToRad(45), rttWidth / rttHeight, 0.1, 100.0);
      gl.uniformMatrix4fv(pMatrixUniform, false, pMatrix);

      mat4.identity(mvMatrix);
      mat4.translate(mvMatrix, mvMatrix, [0, 0, -5.0]);
      mat4.rotate(mvMatrix, mvMatrix, degToRad(canvas.xRotSlider), [0, 1, 0]);
      mat4.rotate(mvMatrix, mvMatrix, degToRad(canvas.yRotSlider), [1, 0, 0]);
      mat4.rotate(mvMatrix, mvMatrix, degToRad(canvas.zRotSlider), [0, 0, 1]);
      gl.uniformMatrix4fv(mvMatrixUniform, false, mvMatrix);

      mat4.invert(nMatrix, mvMatrix);
      mat4.transpose(nMatrix, nMatrix);
      gl.uniformMatrix4fv(nUniform, false, nMatrix);

      // Draw the cube to the FBO
      gl.drawElements(gl.TRIANGLES, 36, gl.UNSIGNED_SHORT, 0);

      // Bind the render-to-texture and generate mipmaps
      gl.bindTexture(gl.TEXTURE_2D, rttTexture);
      gl.generateMipmap(gl.TEXTURE_2D);

      // Bind default framebuffer and setup viewport accordingly
      gl.bindFramebuffer(gl.FRAMEBUFFER, 0);
      gl.viewport(0, 0,
                  canvas.width * canvas.devicePixelRatio,
                  canvas.height * canvas.devicePixelRatio);
      gl.clearColor(0.98, 0.98, 0.98, 1.0);
      gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

      // Calculate and set matrix uniforms
      mat4.perspective(pMatrix, degToRad(45), canvas.width / canvas.height, 0.1, 100.0);
      gl.uniformMatrix4fv(pMatrixUniform, false, pMatrix);

      mat4.identity(mvMatrix);
      mat4.translate(mvMatrix, mvMatrix, [(canvas.yRotAnim - 120.0) / 120.0,
                                          (canvas.xRotAnim -  60.0) / 50.0,
                                          -10.0]);
      mat4.rotate(mvMatrix, mvMatrix, degToRad(canvas.xRotAnim), [0, 1, 0]);
      gl.uniformMatrix4fv(mvMatrixUniform, false, mvMatrix);

      mat4.invert(nMatrix, mvMatrix);
      mat4.transpose(nMatrix, nMatrix);
      gl.uniformMatrix4fv(nUniform, false, nMatrix);

      // Draw the on-screen cube
      gl.drawElements(gl.TRIANGLES, 36, gl.UNSIGNED_SHORT, 0);
  }

  function resizeGL(canvas)
  {
      var pixelRatio = canvas.devicePixelRatio;
      canvas.pixelSize = Qt.size(canvas.width * pixelRatio,
                                 canvas.height * pixelRatio);
  }

  function initBuffers()
  {
      log("        cubeVertexPositionBuffer");
      var cubeVertexPositionBuffer = gl.createBuffer();
      cubeVertexPositionBuffer.name = "cubeVertexPositionBuffer";
      gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
      gl.bufferData(
                  gl.ARRAY_BUFFER,
                  new Float32Array([// Front face
                                          -1.0, -1.0,  1.0,
                                          1.0, -1.0,  1.0,
                                          1.0,  1.0,  1.0,
                                          -1.0,  1.0,  1.0,

                                          // Back face
                                          -1.0, -1.0, -1.0,
                                          -1.0,  1.0, -1.0,
                                          1.0,  1.0, -1.0,
                                          1.0, -1.0, -1.0,

                                          // Top face
                                          -1.0,  1.0, -1.0,
                                          -1.0,  1.0,  1.0,
                                          1.0,  1.0,  1.0,
                                          1.0,  1.0, -1.0,

                                          // Bottom face
                                          -1.0, -1.0, -1.0,
                                          1.0, -1.0, -1.0,
                                          1.0, -1.0,  1.0,
                                          -1.0, -1.0,  1.0,

                                          // Right face
                                          1.0, -1.0, -1.0,
                                          1.0,  1.0, -1.0,
                                          1.0,  1.0,  1.0,
                                          1.0, -1.0,  1.0,

                                          // Left face
                                          -1.0, -1.0, -1.0,
                                          -1.0, -1.0,  1.0,
                                          -1.0,  1.0,  1.0,
                                          -1.0,  1.0, -1.0
                                         ]),
                  gl.STATIC_DRAW);

      gl.enableVertexAttribArray(vertexPositionAttribute);
      gl.vertexAttribPointer(vertexPositionAttribute, 3, gl.FLOAT, false, 0, 0);

      log("        cubeVertexIndexBuffer");
      var cubeVertexIndexBuffer = gl.createBuffer();
      cubeVertexIndexBuffer.name = "cubeVertexIndexBuffer";
      gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
      gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,
                    new Uint16Array([
                                              0,  1,  2,      0,  2,  3,    // front
                                              4,  5,  6,      4,  6,  7,    // back
                                              8,  9,  10,     8,  10, 11,   // top
                                              12, 13, 14,     12, 14, 15,   // bottom
                                              16, 17, 18,     16, 18, 19,   // right
                                              20, 21, 22,     20, 22, 23    // left
                                          ]),
                    gl.STATIC_DRAW);
      gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);

      log("        cubeVerticesTextureCoordBuffer");
      var cubeVerticesTextureCoordBuffer = gl.createBuffer();
      cubeVerticesTextureCoordBuffer.name = "cubeVerticesTextureCoordBuffer";
      gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesTextureCoordBuffer);
      var textureCoordinates = [
                  // Front
                  1.0,  0.0,
                  0.0,  0.0,
                  0.0,  1.0,
                  1.0,  1.0,
                  // Back
                  1.0,  0.0,
                  0.0,  0.0,
                  0.0,  1.0,
                  1.0,  1.0,
                  // Top
                  1.0,  0.0,
                  0.0,  0.0,
                  0.0,  1.0,
                  1.0,  1.0,
                  // Bottom
                  1.0,  0.0,
                  0.0,  0.0,
                  0.0,  1.0,
                  1.0,  1.0,
                  // Right
                  1.0,  0.0,
                  0.0,  0.0,
                  0.0,  1.0,
                  1.0,  1.0,
                  // Left
                  1.0,  0.0,
                  0.0,  0.0,
                  0.0,  1.0,
                  1.0,  1.0
              ];
      gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoordinates),
                    gl.STATIC_DRAW);
      gl.enableVertexAttribArray(textureCoordAttribute);
      gl.vertexAttribPointer(textureCoordAttribute, 2, gl.FLOAT, false, 0, 0);

      var cubeVerticesNormalBuffer = gl.createBuffer();
      cubeVerticesNormalBuffer.name = "cubeVerticesNormalBuffer";
      gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesNormalBuffer);
      gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
                                                                // Front
                                                                0.0,  0.0,  1.0,
                                                                0.0,  0.0,  1.0,
                                                                0.0,  0.0,  1.0,
                                                                0.0,  0.0,  1.0,

                                                                // Back
                                                                0.0,  0.0, -1.0,
                                                                0.0,  0.0, -1.0,
                                                                0.0,  0.0, -1.0,
                                                                0.0,  0.0, -1.0,

                                                                // Top
                                                                0.0,  1.0,  0.0,
                                                                0.0,  1.0,  0.0,
                                                                0.0,  1.0,  0.0,
                                                                0.0,  1.0,  0.0,

                                                                // Bottom
                                                                0.0, -1.0,  0.0,
                                                                0.0, -1.0,  0.0,
                                                                0.0, -1.0,  0.0,
                                                                0.0, -1.0,  0.0,

                                                                // Right
                                                                1.0,  0.0,  0.0,
                                                                1.0,  0.0,  0.0,
                                                                1.0,  0.0,  0.0,
                                                                1.0,  0.0,  0.0,

                                                                // Left
                                                                -1.0,  0.0,  0.0,
                                                                -1.0,  0.0,  0.0,
                                                                -1.0,  0.0,  0.0,
                                                                -1.0,  0.0,  0.0
                                                            ]), gl.STATIC_DRAW);
      gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesNormalBuffer);
      gl.vertexAttribPointer(vertexNormalAttribute, 3, gl.FLOAT, false, 0, 0);
  }

  function initShaders()
  {
      var vertexShader = getShader(gl,
                                   "attribute highp vec3 aVertexNormal;   \
                                    attribute highp vec3 aVertexPosition; \
                                    attribute highp vec2 aTextureCoord;   \

                                    uniform highp mat4 uNormalMatrix;     \
                                    uniform mat4 uMVMatrix;               \
                                    uniform mat4 uPMatrix;                \

                                    varying mediump vec4 vColor;          \
                                    varying highp vec2 vTextureCoord;     \
                                    varying highp vec3 vLighting;         \

                                    void main(void) {                     \
                                        gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);                      \
                                        vTextureCoord = aTextureCoord;                                                        \
                                        highp vec3 ambientLight = vec3(0.5, 0.5, 0.5);                                        \
                                        highp vec3 directionalLightColor = vec3(0.75, 0.75, 0.75);                             \
                                        highp vec3 directionalVector = vec3(0.85, 0.8, 0.75);                                 \
                                        highp vec4 transformedNormal = uNormalMatrix * vec4(aVertexNormal, 1.0);              \
                                        highp float directional = max(dot(transformedNormal.xyz, directionalVector), 0.0);    \
                                        vLighting = ambientLight + (directionalLightColor * directional);                     \
                                    }", gl.VERTEX_SHADER);
      var fragmentShader = getShader(gl,
                                     "varying highp vec2 vTextureCoord;   \
                                      varying highp vec3 vLighting;       \

                                      uniform sampler2D uSampler;         \

                                      void main(void) {                   \
                                          mediump vec3 texelColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t)).rgb;  \
                                          gl_FragColor = vec4(texelColor * vLighting, 1.0);                                       \
                                      }", gl.FRAGMENT_SHADER);

      var shaderProgram = gl.createProgram();
      gl.attachShader(shaderProgram, vertexShader);
      gl.attachShader(shaderProgram, fragmentShader);
      gl.linkProgram(shaderProgram);

      if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
          console.log("Could not initialise shaders");
          console.log(gl.getProgramInfoLog(shaderProgram));
      }

      gl.useProgram(shaderProgram);

      // look up where the vertex data needs to go.
      vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
      gl.enableVertexAttribArray(vertexPositionAttribute);
      textureCoordAttribute = gl.getAttribLocation(shaderProgram, "aTextureCoord");
      gl.enableVertexAttribArray(textureCoordAttribute);
      vertexNormalAttribute =gl.getAttribLocation(shaderProgram, "aVertexNormal");
      gl.enableVertexAttribArray(vertexNormalAttribute);

      pMatrixUniform  = gl.getUniformLocation(shaderProgram, "uPMatrix");
      mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
      nUniform = gl.getUniformLocation(shaderProgram, "uNormalMatrix");

      var textureSamplerUniform = gl.getUniformLocation(shaderProgram, "uSampler")
      gl.activeTexture(gl.TEXTURE0);
      gl.uniform1i(textureSamplerUniform, 0);
  }

  function getShader(gl, str, type) {
      var shader = gl.createShader(type);
      gl.shaderSource(shader, str);
      gl.compileShader(shader);

      if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
          console.log("JS:Shader compile failed");
          console.log(gl.getShaderInfoLog(shader));
          return null;
      }

      return shader;
  }