QQuickFramebufferObject::Renderer::render() not even being called

kaixoo

Hi, I created a small Qt app that demosntrates a basic use case of QQuickFramebufferObject (OpenGL rendering).

I am calling update() but nothing is being rendered:

Repo: https://gitlab.com/kaixoo/app-repro-qml-ogl

You'll need meson to run the project, you can get it like this:

Windows: winget install --id=mesonbuild.meson -e
Debian: sudo apt install meson ninja-build
MacOS: brew install meson

kaixoo

Issue "solved" by calling update() once in the constructor and after every render, although I would prefer more manual control, that can be worked on later.

kaixoo

This is a repro of an issue I'm having with my app, where the FBO only renders when getting resized, and all calls to update() are ignored. In the repro app, I'm not even getting it to render at all.

SGaist

Hi,

Change Canvas by MyCanvas (or something else) in the type registration and QML.

It worked fine after that.

kaixoo

ooooohhh :((
It also worked fine for me after that, which is weird. In my actual application, the canvas is only rendering when it's resized.
I'm subclassing QQuickFramebufferObject::Renderer, do you think the issue could be related to that?

P.S: Actual code is here, all contained in the src/canvas folder: https://gitlab.com/advanced-effects/Advanced-Effects/-/blob/ui/canvas-interactions/src/canvas/view/application_canvas.h?ref_type=heads

SGaist

No, I don't think so.
You just choose to use the same name as an already existing QtQuick type: Canvas

kaixoo

@SGaist No, the name I gave it is ApplicationCanvas, and it renders correctly, so it's not that.

Might it be related to how I'm using Skia? I'm not flushing after every frame because it was causing glitches.
The important skia code is:

	auto fbo = framebufferObject();
        if (!fbo) return;

        m_skia_canvas = obtain_skia_canvas(fbo);

        if (!m_skia_canvas) return;
        draw_to_screen(m_skia_canvas);

kaixoo

Issue "solved" by calling update() once in the constructor and after every render, although I would prefer more manual control, that can be worked on later.

SGaist

@kaixoo said in QQuickFramebufferObject::Renderer::render() not even being called:

@SGaist No, the name I gave it is ApplicationCanvas, and it renders correctly, so it's not that.

Might it be related to how I'm using Skia? I'm not flushing after every frame because it was causing glitches.
The important skia code is:
	auto fbo = framebufferObject();
        if (!fbo) return;

        m_skia_canvas = obtain_skia_canvas(fbo);

        if (!m_skia_canvas) return;
        draw_to_screen(m_skia_canvas);

Sorry, I thought you were still asking about your example !

kaixoo

No problem. By chance, do you know if it's possible to receive input events from a QQuickFramebufferObject? It seems like I'm not getting those: e.g. mousePressEvent, touchEvent, etc.

The methods exist (as it derives from QQuickWidget) and can be overridden but it doesn't seem like they are implemented. Are they?

SGaist

Where are you trying to get these events in your project ?