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<td >Qt 5.12</td><td ><a href="qtgui-index.html">Qt GUI</a></td><td >Hello Vulkan Window Example</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtgui-index.html">Qt 5.12.6 Reference Documentation</a></td>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#startup">Startup</a></li>
<li class="level1"><a href="#the-qvulkanwindow-subclass">The QVulkanWindow Subclass</a></li>
<li class="level1"><a href="#the-actual-rendering">The Actual Rendering</a></li>
<li class="level1"><a href="#running-the-example">Running the Example</a></li>
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<h1 class="title">Hello Vulkan Window Example</h1>
<span class="subtitle"></span>
<!-- $$$hellovulkanwindow-brief -->
<p>Shows the basics of using <a href="qvulkanwindow.html">QVulkanWindow</a>.</p>
<!-- @@@hellovulkanwindow -->
<!-- $$$hellovulkanwindow-description -->
<div class="descr"> <a name="details"></a>
<p>The <i>Hello Vulkan Window Example</i> shows the basics of using <a href="qvulkanwindow.html">QVulkanWindow</a> in order to display rendering with the Vulkan graphics API on systems that support this.</p>
<p class="centerAlign"><img src="images/hellovulkanwindow.png" alt="" /></p><p>In this example there will be no actual rendering: it simply begins and ends a render pass, which results in clearing the buffers to a fixed value. The color buffer clear value changes on every frame.</p>
<a name="startup"></a>
<h2 id="startup">Startup</h2>
<p>Each Qt application using Vulkan will have to have a <code>Vulkan instance</code> which encapsulates application-level state and initializes a Vulkan library.</p>
<p>A <a href="qvulkanwindow.html">QVulkanWindow</a> must always be associated with a <a href="qvulkaninstance.html">QVulkanInstance</a> and hence the example performs instance creation before the window. The <a href="qvulkaninstance.html">QVulkanInstance</a> object must also outlive the window.</p>
<pre class="cpp">
<span class="type"><a href="qvulkaninstance.html">QVulkanInstance</a></span> inst;
<span class="preprocessor">#ifndef Q_OS_ANDROID</span>
inst<span class="operator">.</span>setLayers(<span class="type"><a href="../qtcore/qbytearraylist.html">QByteArrayList</a></span>() <span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_LUNARG_standard_validation"</span>);
<span class="preprocessor">#else</span>
inst<span class="operator">.</span>setLayers(<span class="type"><a href="../qtcore/qbytearraylist.html">QByteArrayList</a></span>()
<span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_GOOGLE_threading"</span>
<span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_LUNARG_parameter_validation"</span>
<span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_LUNARG_object_tracker"</span>
<span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_LUNARG_core_validation"</span>
<span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_LUNARG_image"</span>
<span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_LUNARG_swapchain"</span>
<span class="operator"><</span><span class="operator"><</span> <span class="string">"VK_LAYER_GOOGLE_unique_objects"</span>);
<span class="preprocessor">#endif</span>
<span class="keyword">if</span> (<span class="operator">!</span>inst<span class="operator">.</span>create())
<a href="../qtcore/qtglobal.html#qFatal">qFatal</a>(<span class="string">"Failed to create Vulkan instance: %d"</span><span class="operator">,</span> inst<span class="operator">.</span>errorCode());
</pre>
<p>The example enables validation layers, when supported. When the requested layers are not present, the request will be ignored. Additional layers and extensions can be enabled in a similar manner.</p>
<pre class="cpp">
VulkanWindow w;
w<span class="operator">.</span>setVulkanInstance(<span class="operator">&</span>inst);
w<span class="operator">.</span>resize(<span class="number">1024</span><span class="operator">,</span> <span class="number">768</span>);
w<span class="operator">.</span>show();
</pre>
<p>Once the instance is ready, it is time to create a window. Note that <code>w</code> lives on the stack and is declared after <code>inst</code>.</p>
<a name="the-qvulkanwindow-subclass"></a>
<h2 id="the-qvulkanwindow-subclass">The QVulkanWindow Subclass</h2>
<p>To add custom functionality to a <a href="qvulkanwindow.html">QVulkanWindow</a>, subclassing is used. This follows the existing patterns from <a href="qopenglwindow.html">QOpenGLWindow</a> and <a href="../qtwidgets/qopenglwidget.html">QOpenGLWidget</a>. However, <a href="qvulkanwindow.html">QVulkanWindow</a> utilizes a separate <a href="qvulkanwindowrenderer.html">QVulkanWindowRenderer</a> object. This resembles QQuickFramebufferObject, and allows better separation of the functions that are supposed to be reimplemented.</p>
<pre class="cpp">
<span class="keyword">class</span> VulkanRenderer : <span class="keyword">public</span> <span class="type"><a href="qvulkanwindowrenderer.html">QVulkanWindowRenderer</a></span>
{
<span class="keyword">public</span>:
VulkanRenderer(<span class="type"><a href="qvulkanwindow.html">QVulkanWindow</a></span> <span class="operator">*</span>w);
<span class="type">void</span> initResources() override;
<span class="type">void</span> initSwapChainResources() override;
<span class="type">void</span> releaseSwapChainResources() override;
<span class="type">void</span> releaseResources() override;
<span class="type">void</span> startNextFrame() override;
<span class="keyword">private</span>:
<span class="type"><a href="qvulkanwindow.html">QVulkanWindow</a></span> <span class="operator">*</span>m_window;
<span class="type"><a href="qvulkandevicefunctions.html">QVulkanDeviceFunctions</a></span> <span class="operator">*</span>m_devFuncs;
<span class="type">float</span> m_green <span class="operator">=</span> <span class="number">0</span>;
};
<span class="keyword">class</span> VulkanWindow : <span class="keyword">public</span> <span class="type"><a href="qvulkanwindow.html">QVulkanWindow</a></span>
{
<span class="keyword">public</span>:
<span class="type"><a href="qvulkanwindowrenderer.html">QVulkanWindowRenderer</a></span> <span class="operator">*</span>createRenderer() override;
};
</pre>
<p>The <a href="qvulkanwindow.html">QVulkanWindow</a> subclass reimplements the factory function <a href="qvulkanwindow.html#createRenderer">QVulkanWindow::createRenderer</a>(). This simply returns a new instance of the <a href="qvulkanwindowrenderer.html">QVulkanWindowRenderer</a> subclass. In order to be able to access various Vulkan resources via the window object, a pointer to the window is passed and stored via the constructor.</p>
<pre class="cpp">
<span class="type"><a href="qvulkanwindowrenderer.html">QVulkanWindowRenderer</a></span> <span class="operator">*</span>VulkanWindow<span class="operator">::</span>createRenderer()
{
<span class="keyword">return</span> <span class="keyword">new</span> VulkanRenderer(<span class="keyword">this</span>);
}
VulkanRenderer<span class="operator">::</span>VulkanRenderer(<span class="type"><a href="qvulkanwindow.html">QVulkanWindow</a></span> <span class="operator">*</span>w)
: m_window(w)
{
}
</pre>
<p>Graphics resource creation and destruction is typically done in one of the init - resource functions.</p>
<pre class="cpp">
<span class="type">void</span> VulkanRenderer<span class="operator">::</span>initResources()
{
<a href="../qtcore/qtglobal.html#qDebug">qDebug</a>(<span class="string">"initResources"</span>);
m_devFuncs <span class="operator">=</span> m_window<span class="operator">-</span><span class="operator">></span>vulkanInstance()<span class="operator">-</span><span class="operator">></span>deviceFunctions(m_window<span class="operator">-</span><span class="operator">></span>device());
}
</pre>
<a name="the-actual-rendering"></a>
<h2 id="the-actual-rendering">The Actual Rendering</h2>
<p><a href="qvulkanwindow.html">QVulkanWindow</a> subclasses queue their draw calls in their reimplementation of <a href="qvulkanwindowrenderer.html#startNextFrame">QVulkanWindowRenderer::startNextFrame</a>(). Once done, they are required to call back <a href="qvulkanwindow.html#frameReady">QVulkanWindow::frameReady</a>(). The example has no asynchronous command generation, so the frameReady() call is made directly from startNextFrame().</p>
<pre class="cpp">
<span class="type">void</span> VulkanRenderer<span class="operator">::</span>startNextFrame()
{
m_green <span class="operator">+</span><span class="operator">=</span> <span class="number">0.005f</span>;
<span class="keyword">if</span> (m_green <span class="operator">></span> <span class="number">1.0f</span>)
m_green <span class="operator">=</span> <span class="number">0.0f</span>;
VkClearColorValue clearColor <span class="operator">=</span> {{ <span class="number">0.0f</span><span class="operator">,</span> m_green<span class="operator">,</span> <span class="number">0.0f</span><span class="operator">,</span> <span class="number">1.0f</span> }};
VkClearDepthStencilValue clearDS <span class="operator">=</span> { <span class="number">1.0f</span><span class="operator">,</span> <span class="number">0</span> };
VkClearValue clearValues<span class="operator">[</span><span class="number">2</span><span class="operator">]</span>;
memset(clearValues<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="keyword">sizeof</span>(clearValues));
clearValues<span class="operator">[</span><span class="number">0</span><span class="operator">]</span><span class="operator">.</span>color <span class="operator">=</span> clearColor;
clearValues<span class="operator">[</span><span class="number">1</span><span class="operator">]</span><span class="operator">.</span>depthStencil <span class="operator">=</span> clearDS;
VkRenderPassBeginInfo rpBeginInfo;
memset(<span class="operator">&</span>rpBeginInfo<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="keyword">sizeof</span>(rpBeginInfo));
rpBeginInfo<span class="operator">.</span>sType <span class="operator">=</span> VK_STRUCTURE_TYPE_RENDER_PASS_BEGIN_INFO;
rpBeginInfo<span class="operator">.</span>renderPass <span class="operator">=</span> m_window<span class="operator">-</span><span class="operator">></span>defaultRenderPass();
rpBeginInfo<span class="operator">.</span>framebuffer <span class="operator">=</span> m_window<span class="operator">-</span><span class="operator">></span>currentFramebuffer();
<span class="keyword">const</span> <span class="type"><a href="../qtcore/qsize.html">QSize</a></span> sz <span class="operator">=</span> m_window<span class="operator">-</span><span class="operator">></span>swapChainImageSize();
rpBeginInfo<span class="operator">.</span>renderArea<span class="operator">.</span>extent<span class="operator">.</span>width <span class="operator">=</span> sz<span class="operator">.</span>width();
rpBeginInfo<span class="operator">.</span>renderArea<span class="operator">.</span>extent<span class="operator">.</span>height <span class="operator">=</span> sz<span class="operator">.</span>height();
rpBeginInfo<span class="operator">.</span>clearValueCount <span class="operator">=</span> <span class="number">2</span>;
rpBeginInfo<span class="operator">.</span>pClearValues <span class="operator">=</span> clearValues;
VkCommandBuffer cmdBuf <span class="operator">=</span> m_window<span class="operator">-</span><span class="operator">></span>currentCommandBuffer();
m_devFuncs<span class="operator">-</span><span class="operator">></span>vkCmdBeginRenderPass(cmdBuf<span class="operator">,</span> <span class="operator">&</span>rpBeginInfo<span class="operator">,</span> VK_SUBPASS_CONTENTS_INLINE);
<span class="comment">// Do nothing else. We will just clear to green, changing the component on</span>
<span class="comment">// every invocation. This also helps verifying the rate to which the thread</span>
<span class="comment">// is throttled to. (The elapsed time between startNextFrame calls should</span>
<span class="comment">// typically be around 16 ms. Note that rendering is 2 frames ahead of what</span>
<span class="comment">// is displayed.)</span>
m_devFuncs<span class="operator">-</span><span class="operator">></span>vkCmdEndRenderPass(cmdBuf);
m_window<span class="operator">-</span><span class="operator">></span>frameReady();
m_window<span class="operator">-</span><span class="operator">></span>requestUpdate(); <span class="comment">// render continuously, throttled by the presentation rate</span>
}
</pre>
<p>To get continuous updates, the example simply invokes <a href="qwindow.html#requestUpdate">QWindow::requestUpdate</a>() in order to schedule a repaint.</p>
<a name="running-the-example"></a>
<h2 id="running-the-example">Running the Example</h2>
<p>To run the example from Qt Creator, open the <b>Welcome</b> mode and select the example from <b>Examples</b>. For more information, visit Building and Running an Example.</p>
<p>Files:</p>
<ul>
<li><a href="qtgui-hellovulkanwindow-hellovulkanwindow-cpp.html">hellovulkanwindow/hellovulkanwindow.cpp</a></li>
<li><a href="qtgui-hellovulkanwindow-hellovulkanwindow-h.html">hellovulkanwindow/hellovulkanwindow.h</a></li>
<li><a href="qtgui-hellovulkanwindow-hellovulkanwindow-pro.html">hellovulkanwindow/hellovulkanwindow.pro</a></li>
<li><a href="qtgui-hellovulkanwindow-main-cpp.html">hellovulkanwindow/main.cpp</a></li>
</ul>
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<!-- @@@hellovulkanwindow -->
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