[Interest] Porting Qt5 OpenGL app to Qt6 - QQuickRenderTarget and OpenGL frame buffer object

[Nuno Santos]

Hi,

I have an application that was heavily written on top of OpenGL. Right now I want to port it to Qt 6 with the minimum effort trying to stick to the OpenGL backend until I get the grip on the new things of Qt 6 Graphics API abstraction.

I used to do this in order to assign a target FBO to a QuickWindow:

_quickWindow->setRenderTarget(_fboRender);

This is no longer possible and it requires a QQuickRenderTarget to be created and I seem to have three options:

(since 6.2) QQuickRenderTarget	fromOpenGLRenderBuffer(uint renderbufferId, const QSize &pixelSize, int sampleCount = 1)
(since 6.4) QQuickRenderTarget	fromOpenGLTexture(uint textureId, uint format, const QSize &pixelSize, int sampleCount = 1)
QQuickRenderTarget	fromOpenGLTexture(uint textureId, const QSize &pixelSize, int sampleCount = 1)

I’m trying this:

_renderTarget = QQuickRenderTarget::fromOpenGLRenderBuffer(0, QSize(_renderResolution.width(), _renderResolution.height()));
_quickWindow->setRenderTarget(_renderTarget);

But nothing appears on the screen and I get a warning:

QQuickWindow: No render target (neither swapchain nor custom target was provided)

Can anyone tell me what am I failing here?

Any ideas suggestions are very welcome.

With my best regards,

Nuno