Make it possible to specify device extensions in a future proof manner

Follow the pattern of QQuickRenderTarget and QQuickGraphicsDevice.

This makes it possible to integrate with real world frameworks, such as
OpenXR, that, especially with Vulkan, expect this level of
configurability. (i.e. one pulls the list of extensions to be enabled on
the device, that then needs to be taken into account by Quick, otherwise
it will end up with a VkDevice that is not usable by OpenXR)

Same goes when integrating native Vulkan rendering into an application:
if certain extensions need to be enabled on the VkDevice, today that can
only be done with an environment variable which is not entirely ideal.

These issues are now solved by a new simple (and extensible) container
QQuickGraphicsConfiguration, which is associated with the QQuickWindow.
When applicable, the scene graph will then pick up the relevant settings.

Expand the related docs everywhere. Also rename the vulkanInstance() to
defaultVulkanInstance() to emphasize that it is the instance that is
used for normal QQuickWindows, and is not provided when redirecting
via QQuickRenderControl.

While we are at it, include another obvious candidate: the use-depth-buffer
flag. It turns out that Quick3D's Overlay render mode can be pretty
problematic if Quick writes to the depth buffer. In order to avoid
relying on environment variables (QSG_NO_DEPTH_BUFFER), we now provide
a proper API for controlling that as well.

Change-Id: Iefdb62c1f53de8bd34e3f0d393b00c5020d6188a
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/quick/items/qquickrendercontrol.cpp b/src/quick/items/qquickrendercontrol.cpp
index 51483bce57..c2adc2ef10 100644
--- a/src/quick/items/qquickrendercontrol.cpp
+++ b/src/quick/items/qquickrendercontrol.cpp
@@ -270,6 +270,14 @@ int QQuickRenderControl::samples() const
     specify an appropriate QQuickGraphicsDevice, wrapping existing graphics
     objects, by calling QQuickWindow::setGraphicsDevice().
 
+    To configure which device extensions to enable (for example, for Vulkan),
+    call QQuickWindow::setGraphicsConfiguration() before this function.
+
+    \note When using Vulkan, QQuickRenderControl does not create a
+    QVulkanInstance automatically. Rather, it is the application's
+    responsibility to create a suitable QVulkanInstance and
+    \l{QWindow::setVulkanInstance()}{associate it} with the QQuickWindow.
+
     \note This function does not need to be, and must not be, called when using
     the \c software adaptation of Qt Quick.