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<td >Qt 5.9</td><td ><a href="qtcanvas3d-index.html">Qt Canvas 3D</a></td><td ><a href="qtcanvas3d-examples.html">Qt Canvas 3D Examples</a></td><td >Framebuffer Example</td></tr></table><table class="buildversion"><tr>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#preparing-the-framebuffer">Preparing the Framebuffer</a></li>
<li class="level1"><a href="#creating-the-texture">Creating the Texture</a></li>
<li class="level1"><a href="#rendering-into-the-framebuffer">Rendering into the Framebuffer</a></li>
<li class="level1"><a href="#using-the-framebuffer-as-a-texture">Using the Framebuffer as a Texture</a></li>
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<h1 class="title">Framebuffer Example</h1>
<span class="subtitle"></span>
<!-- $$$framebuffer-description -->
<div class="descr"> <a name="details"></a>
<p>The Framebuffer Example shows how to render into a framebuffer, create a texture of it, and apply the texture to an object in normal on-screen rendering.</p>
<p>The example has a moving and rotating cube, which has another textured cube drawn into it via the framebuffer object. The cube in the framebuffer can be rotated using Sliders from Qt Quick Controls.</p>
<p class="centerAlign"><img src="images/framebuffer-example.png" alt="" /></p><a name="preparing-the-framebuffer"></a>
<h2 id="preparing-the-framebuffer">Preparing the Framebuffer</h2>
<p>We first define the variables we need for the render-to-texture framebuffer:</p>
<pre class="js">
var <span class="name">rttFramebuffer</span>;
var <span class="name">rttTexture</span>;
var <span class="name">rttWidth</span> = <span class="number">512</span>;
var <span class="name">rttHeight</span> = <span class="number">512</span>;
</pre>
<p>Then, in the <code>initializeGL</code> function, we create the framebuffer object:</p>
<pre class="js">
<span class="comment">// Create the framebuffer object</span>
<span class="name">rttFramebuffer</span> <span class="operator">=</span> <span class="name">gl</span>.<span class="name">createFramebuffer</span>();
<span class="name">rttFramebuffer</span>.<span class="name">name</span> <span class="operator">=</span> <span class="string">"OffscreenRenderTarget"</span>;
<span class="name">gl</span>.<span class="name">bindFramebuffer</span>(<span class="name">gl</span>.<span class="name">FRAMEBUFFER</span>, <span class="name">rttFramebuffer</span>);
</pre>
<a name="creating-the-texture"></a>
<h2 id="creating-the-texture">Creating the Texture</h2>
<p>After the creation of the framebuffer, we create the texture:</p>
<pre class="js">
<span class="comment">// Create the texture</span>
<span class="name">rttTexture</span> <span class="operator">=</span> <span class="name">gl</span>.<span class="name">createTexture</span>();
<span class="name">rttTexture</span>.<span class="name">name</span> <span class="operator">=</span> <span class="string">"OffscreenRenderTargetTexture"</span>;
<span class="name">gl</span>.<span class="name">bindTexture</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>, <span class="name">rttTexture</span>);
<span class="name">gl</span>.<span class="name">texParameteri</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>, <span class="name">gl</span>.<span class="name">TEXTURE_MAG_FILTER</span>, <span class="name">gl</span>.<span class="name">LINEAR</span>);
<span class="name">gl</span>.<span class="name">texParameteri</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>, <span class="name">gl</span>.<span class="name">TEXTURE_MIN_FILTER</span>, <span class="name">gl</span>.<span class="name">LINEAR_MIPMAP_NEAREST</span>);
<span class="name">gl</span>.<span class="name">texImage2D</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>, <span class="number">0</span>,
<span class="name">gl</span>.<span class="name">RGBA</span>, <span class="name">rttWidth</span>, <span class="name">rttHeight</span>,
<span class="number">0</span>, <span class="name">gl</span>.<span class="name">RGBA</span>, <span class="name">gl</span>.<span class="name">UNSIGNED_BYTE</span>,
<span class="number">null</span>);
<span class="name">gl</span>.<span class="name">generateMipmap</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>);
</pre>
<p>Then we need to bind the texture as a color attachment, create and bind a render buffer, and bind the depth attachment:</p>
<pre class="js">
<span class="comment">// Bind the texture as color attachment, create and bind a depth buffer</span>
<span class="name">gl</span>.<span class="name">framebufferTexture2D</span>(<span class="name">gl</span>.<span class="name">FRAMEBUFFER</span>,
<span class="name">gl</span>.<span class="name">COLOR_ATTACHMENT0</span>,
<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>, <span class="name">rttTexture</span>, <span class="number">0</span>);
var <span class="name">renderbuffer</span> = <span class="name">gl</span>.<span class="name">createRenderbuffer</span>();
<span class="name">gl</span>.<span class="name">bindRenderbuffer</span>(<span class="name">gl</span>.<span class="name">RENDERBUFFER</span>, <span class="name">renderbuffer</span>);
<span class="name">gl</span>.<span class="name">renderbufferStorage</span>(<span class="name">gl</span>.<span class="name">RENDERBUFFER</span>,
<span class="name">gl</span>.<span class="name">DEPTH_COMPONENT16</span>,
<span class="name">rttWidth</span>, <span class="name">rttHeight</span>);
<span class="name">gl</span>.<span class="name">framebufferRenderbuffer</span>(<span class="name">gl</span>.<span class="name">FRAMEBUFFER</span>,
<span class="name">gl</span>.<span class="name">DEPTH_ATTACHMENT</span>,
<span class="name">gl</span>.<span class="name">RENDERBUFFER</span>, <span class="name">renderbuffer</span>);
</pre>
<a name="rendering-into-the-framebuffer"></a>
<h2 id="rendering-into-the-framebuffer">Rendering into the Framebuffer</h2>
<p>In <code>paintGL</code> function, we first need to draw the scene into the framebuffer. We start by binding the framebuffer object and setting a viewport:</p>
<pre class="js">
<span class="comment">// bind the FBO and setup viewport</span>
<span class="name">gl</span>.<span class="name">bindFramebuffer</span>(<span class="name">gl</span>.<span class="name">FRAMEBUFFER</span>, <span class="name">rttFramebuffer</span>);
<span class="name">gl</span>.<span class="name">viewport</span>(<span class="number">0</span>, <span class="number">0</span>, <span class="name">rttWidth</span>, <span class="name">rttHeight</span>);
</pre>
<p>Then, we need to bind the loaded texture we want to use in rendering into the framebuffer object:</p>
<pre class="js">
<span class="comment">// Bind the loaded texture</span>
<span class="name">gl</span>.<span class="name">bindTexture</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>, <span class="name">cubeTexture</span>);
</pre>
<p>And then we can draw the textured cube into the framebuffer:</p>
<pre class="js">
<span class="comment">// Draw the cube to the FBO</span>
<span class="name">gl</span>.<span class="name">drawElements</span>(<span class="name">gl</span>.<span class="name">TRIANGLES</span>, <span class="number">36</span>, <span class="name">gl</span>.<span class="name">UNSIGNED_SHORT</span>, <span class="number">0</span>);
</pre>
<a name="using-the-framebuffer-as-a-texture"></a>
<h2 id="using-the-framebuffer-as-a-texture">Using the Framebuffer as a Texture</h2>
<p>First, we bind the render-to-texture right after drawing, and generate mipmaps:</p>
<pre class="js">
<span class="comment">// Bind the render-to-texture and generate mipmaps</span>
<span class="name">gl</span>.<span class="name">bindTexture</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>, <span class="name">rttTexture</span>);
<span class="name">gl</span>.<span class="name">generateMipmap</span>(<span class="name">gl</span>.<span class="name">TEXTURE_2D</span>);
</pre>
<p>Then we need to bind the default framebuffer (screen), and set up the viewport:</p>
<pre class="js">
<span class="comment">// Bind default framebuffer and setup viewport accordingly</span>
<span class="name">gl</span>.<span class="name">bindFramebuffer</span>(<span class="name">gl</span>.<span class="name">FRAMEBUFFER</span>, <span class="number">0</span>);
<span class="name">gl</span>.<span class="name">viewport</span>(<span class="number">0</span>, <span class="number">0</span>,
<span class="name">canvas</span>.<span class="name">width</span> <span class="operator">*</span> <span class="name">canvas</span>.<span class="name">devicePixelRatio</span>,
<span class="name">canvas</span>.<span class="name">height</span> <span class="operator">*</span> <span class="name">canvas</span>.<span class="name">devicePixelRatio</span>);
</pre>
<p>And finally, we draw the on-screen view:</p>
<pre class="js">
<span class="comment">// Draw the on-screen cube</span>
<span class="name">gl</span>.<span class="name">drawElements</span>(<span class="name">gl</span>.<span class="name">TRIANGLES</span>, <span class="number">36</span>, <span class="name">gl</span>.<span class="name">UNSIGNED_SHORT</span>, <span class="number">0</span>);
</pre>
<p>Files:</p>
<ul>
<li><a href="qtcanvas3d-framebuffer-qml-framebuffer-framebuffer-js.html">framebuffer/qml/framebuffer/framebuffer.js</a></li>
<li><a href="qtcanvas3d-framebuffer-qml-framebuffer-main-qml.html">framebuffer/qml/framebuffer/main.qml</a></li>
<li><a href="qtcanvas3d-framebuffer-main-cpp.html">framebuffer/main.cpp</a></li>
<li><a href="qtcanvas3d-framebuffer-framebuffer-pro.html">framebuffer/framebuffer.pro</a></li>
<li><a href="qtcanvas3d-framebuffer-framebuffer-qrc.html">framebuffer/framebuffer.qrc</a></li>
</ul>
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