Sunday, March 12, 2017

QNanoPainter with Qt 5.8 (and QSGRenderNode)

QNanoPainter recently gained initial support for QSGRenderNode which is a new public class available starting from Qt 5.8. What this means is that instead of rendering through FBO using QQuickFramebufferObject so, OpenGL drawing is done directly into Qt Quick Scene Graph. And as a QQuickItem somewhere in the middle of scene, not just underlay/overlay for the scene which was already possible before Qt 5.8 using beforeRendering & afterRendering.

Below is a video running QNanoPainter tester app on MacBook Pro with 16 unique QQuickItems using QSGRenderNode mode:

So should you enable QNANO_USE_RENDERNODE with your custom QNanoPainter items?

  • There is a potential performance gain for not rendering through FBO. Especially if your UI contains many custom items and/or you resize items, QSGRenderNode may give more gains as FBO resizing can be costly.
  • However, based on my testing with few different Android devices the performance difference seems pretty small, just few percentages. Maybe with some less performant embedded platforms which are bad with FBOs there is a bigger difference.
  • With QQuickFramebufferObject, rendering is always clipped to FBO size, so item clip true/false property doesn’t have any effect. With QSGRenderNode such clipping doesn’t automatically happen, instead each item can freely paint anywhere outside its rect. Whether this is pros or cons is up to your use case, but good to note anyway.
  • With QSGRenderNode, standard QQuickItem features (position, rotation, clipping, scaling etc.) need to be implemented customly. QNanoPainter doesn’t (yet) fully support clipping of QML item tree so if you have several clip regions and/or rotate these items, clipping doesn’t necessarily behave as expected when using QNANO_USE_RENDERNODE.
  • When your item doesn’t need to be repainted, just re-rendered, it’s more performant to render the FBO. So if your items don’t change often it might be better not to enable QNANO_USE_RENDERNODE.

So with all above said, QNANO_USE_RENDERNODE is not currently enabled by default even when building with Qt 5.8. But that might change somewhere in future if gains seem worth it. For now please upgrade your QNanoPainter library and test how it works for you.

Sunday, January 24, 2016

QNanoPainter - a brief update

QNanoPainter has been now publicly available for about a month and during this time has seen some nice improvements.

Gunnar first added Windows support, then worked on reducing QNanoQuickItemPainter creation time and memory consumption with multiple items. Niels and Jean-Michaƫl did some performance testing on Linux & NVIDIA shield, results discussed in issue 6. Examples Gallery was restructured and now contains 3 examples: QNanoPainter Features, Mouse Event Boxes, and Freehand Painting.

Here’s what they look on Nexus 6:

(best viewed in HD)

So, if you are working with Qt5 and have a need for custom QQuickItems, I warmly recommend checking out QNanoPainter. Thanks to everyone involved!

Friday, December 25, 2015

QNanoPainter Available!

About 2.5 months ago I introduced QNanoPainter project for implementing custom QQuickItems. We’ve been really busy (and continue to be so) with other things but took now the time to push QNanoPainter publicly available for wider audience in here:

It’s not ready (as software never is), but already quite capable for serious kicking of tires. Just clone it, build with Qt Creator / qmake and run the provided examples. And when you want to try implementing own items, straightforward instructions to get started are available at front-page README.

If you dig it and want to assist in improving QNanoPainter, here are few ideas for patches:

  • We have tested QNanoPainter on OS X, Linux, Android and iOS. What’s missing at least is making it work on Windows (with dynamic OpenGL build of Qt).
  • Documentation with QDoc has been started but it’s not complete. There are plenty of ”TODO: Write more documentation here” comments in classes and documentation could overall be improved and styled.
  • Current NanoVG version used is from fork at bfbac9a35e, with some additions. Custom additions are marked with ”// ### Added”. Some reasons to go with this fork for now instead of upstream are discussed in What should be done is to update NanoVG to some latest version, apply additions and test properly. Maybe own NanoVG fork with additions should be maintained?
  • Instead of stb_truetype and stb_image code could be ported to use Qt for images and texts. I think at least text rendering would require private Qt headers and additions in Qt side, so may not be that straightforward.
  • Bugfixes!

We received some good comments already and hopefully now more & patches when sources are publicly available. I’ll write some more blog posts later, but now.. Clone!

Sunday, October 4, 2015

Introducing QNanoPainter

Qt World Summit is just about to start! I’m not participating this time, but wanted to contribute one-more-thing to discuss in UI groups at the heart of Berlin ;)

During the past about six months we at QUIt Coding have had a side-side-project called QNanoPainter. This library is designed for implementing custom QQuickItems into Qt5 scene graph. Currently if you want to implement custom Qt Quick item, options are at least:

  • QQuickItem: Offers best performance due to Qt5 scene graph integration. But QSG* classes are relatively low-level with vertices, indices & materials. Painting more complicated things requires quite an expert and even then productivity is not very high.
  • QQuickFramebufferObject: This is a good option if you want to draw with OpenGL into QQuickItem. But as we all know, OpenGL is also quite low-level API so no productivity wins here.
  • QQuickPaintedItem: This means painting with good old QPainter C++ API. Weakness of QPainter with modern graphics accelerated hardware is that you either get good antialiased quality (QImage rendering target) or fast OpenGL painting (FBO rendering target) but not both. Qt raster engine is very good CPU backend but GPUs are ruling the world these days. And QPainter OpenGL backend doesn’t itself support antialiasing, it requires multisampling with GL_EXT_framebuffer_multisample and GL_EXT_framebuffer_blit extensions as explained here by Laszlo. In case you set FBO target and antialiasing on with hardware that doesn’t support these (e.g. Nexus6 and iPhone6), target with automatically switch back to QImage & raster with performance dipping on most devices.
  • QtQuick Canvas: Canvas item is implemented on top of QPainter so it has mostly same cons and pros as QQuickPaintedItem. HTML5 Canvas API is nice and popular but there is some overhead from (QPainter) API mismatch and JavaScript especially if more drawing data needs to be exported from C++ side.
  • QML ShaderEffect: As you can’t really mess with the mesh, this approach suits for simple cases where fragment shader is enough. But we are now thinking a bit more complicated items where this option isn’t enough or at least becomes complicated and slow.

So isn’t these options enough, still need something else? Yes, I think so.

QNanoPainter is our novel approach for trying to offer performance, productivity and rendering quality all in one. In a nutshell QNanoPainter is:

  • Excellent NanoVG OpenGL library as a drawing backend with some patches for performance & features.
  • QNanoPainter C++ API on top of NanoVG (which is written with C). This API is mixture of QPainter and HTML5 canvas APIs. Offers vector drawing, images and text rendering with classes such as QNanoPainter, QNanoFont, QNanoImagePattern, QNanoLinearGradient etc.
  • QNanoQuickItem to implement items into Qt Quick scene graph. Basically it’s like QQuickPaintedItem, but instead of QPainter offers QNanoPainter API for drawing.
  • Some examples like QNanoPainter vs. QPainter demo and Gallery, more to come.

One thing we have tried is to implement demo with same painting result using QPainter (QQuickPaintedItem) and QNanoPainter (QNanoQuickItem). Performance comparison is always tricky (and it’s not just about performance), but with comparable antialiased painting we are seeing 3-10 times better performance with QNanoPainter depending on hardware, content, item sizes etc. Here’s a short video showing this demo running on iPhone6 and Nexus6 with all tests on (iPhone6 in fact painting everything twice to get more juice out of it):

(best viewed in HD)

QNanoPainter is still work-in-progress and not ready for releasing. But we would like to hear what others think: Which (of the above) options do you use for custom QML items? Have you had issues finding suitable option for some use-cases? If yes, what features have you missed and would like to have?

Just comment here, tweet with #qnanopainter or email to info{at}, thanks!

Sunday, March 9, 2014

QML and Recursive Shaders

Let's say that you want your Qt5/QML UI to contain sort of a graph. Instead of presenting just the current value, your want user to see few seconds into history how the value has changed. Something like this:

To implement the above component with Qt5 & QML, there are at least 3 possibilities:
1) Use QML Canvas and draw the graph using JavaScript.
2) Use QQuickPaintedItem and draw the graph using C++ QPainter APIs.
3) Use QQuickItem and draw using OpenGL and QSG* helpers.

First of these is "easiest", no C++ is required but performance and features go along HTML5 canvas API. Second one is good for those familiar with QPainter, but it also has a small performance cost as rendering goes either through QImage or FBO. Third QQuickItem option performs the best and is optimal for Qt5 scene graph, but working with scene graph QSG* classes and OpenGL can feel a bit too low level.

As the title of this blog post suggest, there is also a candidate number 4: Use a recursive shader.

QML ShaderEffectSource provides a property "recursive" which doesn't seem to be widely known. Story goes that Kim #1 asked Kim #2 to provide this feature and it was implemented during summer 11' with this commit. But none of the Qt examples (even now at Qt 5.2.1) demonstrate the usage so it got lost somehow... until now, my precious *gollum* *gollum*.

When setting the recursive property to true, ShaderEffectSource allocates an extra texture to store the rendering result and this texture can then be used as a source for ShaderEffect. Effectively this means that instead of rendering into a clean sheet, ShaderEffect can utilize the previous frame. And this of course opens up many possibilities.

Our component which demonstrates recursive shader usage is called 'QUItMeterComponent'. As explained, recursive ShaderEffectSource needs to allocate an extra texture of its size. Keeping the texture small increases performance and reduces graphics memory usage, so this sounds like a perfect opportunity to utilize modified LedScreen component presented earlier. As each pixel equals to a led, it allows presenting small source (left) as a nice ledscreen (right).

Now we just add a bit sugar with a mirror effect and feed our QUItMeterComponent with QtSensors accelerometer data. Outcome is G-force app which looks in Nexus4 like this:

If you think this component might suit your needs and/or want get a small example of using recursive ShaderEffectSource, sources of this G-force app are available from:

Thursday, October 24, 2013

QUIt demos on Android

Qt 5.2 Beta was released on yesterday, whey! As many of us know already, Qt 5.2 will be the first Qt version with an official Android support. Qt 5.2 will also contain quite a big changes on the UI side, with the new V4 JavaScript engine and the Scene Graph renderer. So how well does this beta run existing Qt Quick 2.0 applications on Android?

We have made numerous UI demos in the past so I decided to install Qt 5.2 beta into Nexus 7 (2013) and put it into test! Here's video:

Overall I'm impressed by the quality. Qt Creator is able to setup Android projects with ease, things work and performance is very good. What more could one ask?

I encourage everyone to test this beta and report bugs so we'll get things close to perfection before 5.2.0 release, due by the end of November. Keep calm and hack on!

Monday, May 13, 2013

Qt5 Battery Component

After the QUItIndicator trilogy which introduced idea, design and performance of a specific Qt5 QML component there's room for more, right?! Something like this:

This time we have a dynamic QML component for showing the remaining power of your mobile device battery. As a recap, with "Dynamic QML component" I mean someting which utilizes not only basic QML animation properties (position, opacity, scale etc.) but also new Qt5 features (shaders, particles, scenegraph powa!) to appear "more dynamic". Maybe it's just me, but I would love to see UIs really utilizing modern GPUs... and accelerating this progress is one of the reasons why I code these examples and blog about them. Another reason being to rule-the-world, obviously ;-P

Instead of explaining design & features of QUItBattery component I'll let this video to do that:

If you want to use this liquid battery component in your UI: Download the sources from here, copy QUItBatteryComponent directory, import it in your QML and off you go. Happy hacking!