- Qt 6.9
- Qt GUI
- Hello Vulkan Triangle Example
- Qt 6.9.2 Reference Documentation

# Hello Vulkan Triangle Example

Shows the basics of rendering with QVulkanWindow and the Vulkan API.

The Hello Vulkan Triangle Example creates a full graphics pipeline, including a vertex and fragment shader, to render a triangle.

#### Startup

Each Qt application using Vulkan will have to have a `Vulkan instance` which encapsulates application-level state and initializes a Vulkan library.

A QVulkanWindow must always be associated with a QVulkanInstance and hence the example performs instance creation before the window. The QVulkanInstance object must also outlive the window.

         QVulkanInstance inst;
         inst.setLayers({ "VK_LAYER_KHRONOS_validation" });
         if (!inst.create())
             qFatal("Failed to create Vulkan instance: %d", inst.errorCode());

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.

         VulkanWindow w;
         w.setVulkanInstance(&inst);

         w.resize(1024, 768);
         w.show();

Once the instance is ready, it is time to create a window. Note that `w` lives on the stack and is declared after `inst`.

#### The QVulkanWindow Subclass

To add custom functionality to a QVulkanWindow, subclassing is used. This follows the existing patterns from QOpenGLWindow and QOpenGLWidget. However, QVulkanWindow utilizes a separate QVulkanWindowRenderer object.

The QVulkanWindow subclass reimplements the factory function QVulkanWindow::createRenderer(). This simply returns a new instance of the QVulkanWindowRenderer 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.

     class VulkanWindow : public QVulkanWindow
     {
     public:
         QVulkanWindowRenderer *createRenderer() override;
     };

#### The Actual Rendering

QVulkanWindow subclasses queue their draw calls in their reimplementation of QVulkanWindowRenderer::startNextFrame(). Once done, they are required to call back QVulkanWindow::frameReady(). The example has no asynchronous command generation, so the frameReady() call is made directly from startNextFrame(). To get continuous updates, the example simply invokes QWindow::requestUpdate() in order to schedule a repaint.

The example also demonstrates multisample antialiasing. Based on the supported sample counts reported by QVulkanWindow::supportedSampleCounts() the example chooses between 8x, 4x, or no multisampling. Once configured via QVulkanWindow::setSamples(), QVulkanWindow takes care of the rest: the additional multisample color buffers are created automatically, and resolving into the swapchain buffers is performed at the end of the default render pass for each frame.

#### Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, see Qt Creator: Tutorial: Build and run.

Example project @ code.qt.io