Qt for Device Creation

Nils Christian Roscher-Nielsen

Product Manager, The Qt Company

© 20152

Overview

• Problems facing device creators• How Qt for Device Creation addresses those problems

• Boot to Qt pre-built reference stack

• Demonstrations

• Performance improvement tools• Qt Quick 2D renderer

• Qt Quick compiler

• QML Profiler

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Problems facing Device Creators (Software)

• Finding an Software Development Kit

• Interfacing with Hardware

• Finding Middleware to accelerate development

• Tooling that enables rapid iterative development

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Software Development Kits for Device Creation

• System Images• Software that runs on the hardware

• Toolchain• Compilers

• Tools

• Sysroot• Development files for system image

Operating System SDKLinux

• Yocto

• Buildroot

• Ubuntu/Debian

• Board Support Packages (BSP)• Linux kernel (patches)

• Graphics Drivers

• Radio hardware firmware

• Wi-Fi

• Bluetooth

• NFC

• GSM

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Operating System SDKOther

• AOSP (Android Open Source Project)• Linux/Android Kernel

• Standardized platform

• Windows Embedded• Pre built images from the HW vendor

• Microsoft provides and controls the SDK and tooling

• QNX

• VxWorks• Need to go through the OS vendor to get image and SDK

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Interfacing with Device Hardware

• Camera and Sensors

• GPU • OpenGL

• OpenCL/CUDA

• Radio (Wi-Fi, Bluetooth, NFC)

• Serial, CAN, i2c

• Audio

• Display

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Application

Qt Libraries

Platform Native Interfaces

Linux AndroidWindows

EmbeddedQNX VxWorks

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Accelerating Development with Qt Middleware

• User Interface Primitives • Buttons, Checkboxes, Radio Buttons

• Views

• Easily converting designer’s vision into a User Interface • Look and Feel

• Internationalization Support

• Input methods (Virtual Keyboards, remote controls)

• Integrated Web Browser

• Multimedia playback

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Qt Developer Offering, Cross-Platform APIs

GUI

non-GUI

Essentials

Add-onsWidgets

C++Native LAFLayoutsStylesOpenGL

Qt Quick

QMLControlsLayoutsStylesOpenGL

WebEngine+ WebView

HTML 5Hybrid UIs SVG

Canvas 3D

Serial PortCore

ProcessesThreadsIPCContainersI/OStringsEtc.

Multimedia

AudioVideoRadioCamera

Sql

SQL and Oracle databases

Network

HTTPFTPTCP/UDPSSL

Qt Test

Bluetooth

Positioning Concurrency

Printing Scripting

NFC Platform Extras

XML Sensors

Image formats

Charts

In-App Purchasing

Data Visualization

Virtual Keyboard

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Tooling for Rapid Iterative Development

• IDE (Integrated Development Environment)

• Ease of deployment to devices

• Remote debugging and profiling

• Simulation/Emulation of devices

Qt Creator

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Qt UI Offering – Choose the Best of All Worlds

Qt Quick

C++ on the back, declarative UI design

(QML) in the front for beautiful,

modern touch-based User

Experiences.

Qt Widgets

Customizable C++ UI controls for

traditional desktop look-and-feel. Also

good for more static embedded UIs

for more limited devices / operating

systems.

Web / Hybrid

Use HTML5 for dynamic web

documents, Qt Quick for native

interaction.

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Rapid Workflow with Qt Quick

Developer

Declarative UI Design

Modern User Interfaces, written with QML. Ideal for rapid UI prototyping.

Imperative Logic

Power of Cross-Platform Native Qt/C++

Core

Processes, Threads,IPC, Containers,I/O, Strings,etc.

Network

HTTPFTPSSL

Sql

SQL &OracleDatabases

XM

L

Blu

eto

oth

Po

siti

on

ing

NFC

Se

ria

l Po

rt

Designer

+ Direct Hardware Access

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Boot to Qt Pre-built Reference Stack

• Lightweight Linux stack• Without X11 (targets fbdev)

• Minimum dependencies to enable most Qt features

• Images and full development environment available for reference hardware

• Build scripts to further customize the image and SDK for your needs

Immediate Prototyping with a

Reference Stack: Boot to Qt

Demo Time!

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Embedded Linux: Building your own Qt

• Toolchain

• Sysroot• Yocto/Buildroot

• Existing image

• Host machine vs Target Image

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Qt Configure Arguments for Cross-Compilation

• -prefix /usr/local• Intended install directory on device

• -extprefix $SYSROOT/usr/local• Location installed on host machine by “make install”

• -host prefix ~/Qt-build/• Location to install host tools (qmake, moc, uic…)

• -sysroot $SYSROOT

• -device rasp-pi• Name of the devices mkspec you are targeting

• -device-option CROSS_COMPILE=${location_of_toolchain}

Improving the performance

of your applications

Qt Quick Profiler

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Why do you need a Profiler

• Classic optimization• Minimize the total time a program takes

• Instrument your binary to count and time function calls

• Run in an emulator to keep track of function calls

• Create Call statistics to see

• Which functions took the most time

• Which functions are called most often

• Go back and optimize

• This is not always very helpful in a Qt Quick application

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Challenges

• JIT compiled QML makes little sense in tools like Valgrind• Which functions are called?

• No symbolic information available

• Stack unwinding only with emulating profilers

• Mainly statistical information

• 40 ms event handler• No big deal statistically

• When it happens is important

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Challenges “Many” Calls

• Time for each object creation is not very important

• Number of calls a bit more interesting, but …

• Their distribution over the time frames is most important

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The QML Profiler

• Analyze modein Qt Creator1. Start/Stop profiling

2. Control execution directly or profile external process

3. Switch recording on and off while the application is running

4. Select event types to be recorded

5. Clear current trace

• Save and load traces from the context menu

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• Pixmap Cache• Slow loading or large pictures

• Scene Graph, Animations• Composition of the Scene Graph

• Memory usage• JavaScript heap and garbage collector

• Binding, Signal Handling, JavaScript, etc.• QML and JavaScript execution time

Timeline View

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• Statistical profile of QML/JavaScript

• For problems that lend themselves to the classical workflow

• Optimize the overall most expensive parts of the application to get a general speedup

Events View

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• Too much JavaScript in each frame

• All JavaScript must return before GUI thread advances

• Frames delayed/dropped if GUI thread not ready

• Result: Unresponsive, stuttering UI

• Creating/Painting/Updating invisible items?

• Takes time in GUI thread

• Same effect as “Too much JavaScript”

• Triggering long running C++ functions?

• Paint methods, signal handlers, etc. triggered from QML

• Also takes time in GUI thread

• Harder to see in the QML profiler as C++ isn’t profiled

My application is slowWhat is wrong?

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• Watch frame rate in Animations and Scene Graph

• Gaps and orange animation events are bad

• JavaScript category shows functions and run time

• Stay under 1000/60 ≈ 16ms per frame

Too much JavaScript

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• Check again for dropped frames

• Check for many short bindings or signal handlers => Too many items updated per frame

• QSG_VISUALIZE=overdraw shows scene layout

• Are items outside the screen or underneath visible elements

Invisible Items

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• Dropped frames, but no JavaScript running?

• Large unexplained gaps in the timeline?

• Check your custom QQuickItem implementations

• Use general purpose profiler to explore the details

Long Running C++ functions

Qt Quick 2D Renderer

Qt Quick 2D renderer

• Renders Qt Quick without OpenGL

• Can render fully in Software

• Makes use of 2D Hardware acceleration

• DirectFB (Linux)

• Direct 2D (Windows)

• Others possible

Qt Quick 2

Scene Graph

OpenGL QPainter

Direct2D DirectFb LinuxFb

Qt Quick 2D Renderer

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What is the Qt Quick 2D Renderer?

Qt Quick 2

QML SceneGraph

SceneGraph Adaptation Layer

Qt Quick 2D Render

QPainter QBackingStore

OpenGL Batch Render

OpenGL (ES) 2.0

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Problems Qt Quick 2D Renderer Addresses

• No GPU, or no OpenGL 2.0 support

• No requirement for:• Particles

• 60 FPS animations

• “Eye Candy”

• Same UI across device portfolio

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Simple to use

• export QMLSCENE_DEVICE=softwarecontext

• But make sure you are not using unsupported features.

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2D Hardware Acceleration with QBlittable

QBackingStore

QPixmap

fillRect

alphaFillRect

drawPixmap

drawPixmapOpacity

drawCachedGlyphs

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Qt Quick 2 Limitations with the 2D Renderer

• ShaderEffect

• Particles

• Sprites

• Custom Items with OpenGL

• RenderControls

© 2015

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Not Just for Embedded

• Works anywhere QWidget works• Uses the same rendering path as QWidgets

• No dependency on QWidgets Module

• Desktop Platforms• Windows (remove OpenGL dependency)

• Linux (X11 Forwarding)

• Remote Desktop

© 2015

Future of 2D renderer

• OpenVG• Possible to add support

• Not planned at the moment

• Let us know if you are interested

• New Hardware• Moving beyond DirectFB

• Partnering with HW vendors

• Customer requests

• Many improvements to come• Close collaboration with users

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Qt Quick Compiler

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Background

• Qt Quick applications consist traditionally of a mixture of• C++ code

• Declarative QML files with embedded, imperative JavaScript code

• Additional resources such as PNG image files

• C++ code gets compiled to native code in target architecture

• PNG image files and other resource get embedded into the resulting binary through the Qt Resource System

• QML source files need to be deployed verbatim to the target device

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Introducing Qt Quick Compiler

• Allows for compilation of .qml and .js files in Qt Quick applications ahead of time

• Output is portable C++ code that is compiled alongside the application C++ code

• Embedded in the final application binary

• Requires a commercial Qt license

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Memory Consumption: Example Samegame

• Environment: Linux, armv7, release build

• Without Qt Quick Compiler:• smaps reports:

• Private_Clean: 4076 kB

• Private_Dirty: 12744 kB

• With Qt Quick Compiler:• Private_Clean: 4652 kB

• Private_Dirty: 11976 kB

• ~600 kB memory became mmap()’able from disk

• Merely by flipping a switch in the build system

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Start-up time: Same game example

• Platform: Linux, x86-64

• Counting instructions with callgrind (stable)

• Without Qt Quick Compiler:• ~461 Million Instructions for startup

• With Qt Quick Compiler:• ~339 Million Instructions for startup

• 27% instructions saved, merely by flipping a switch in the build system

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Run-time Performance Implications

• Qt Quick Compiler generated code is about as fast as Just-In-Time compiler in average• Where JIT is available

• Just-In-Time compilation not supported on all platforms

• Fallback to byte-code interpreter on PowerPC, MIPS, etc.

• Qt Quick Compiler gives ~2x speed-up• Where JIT not available

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Summary

• Port your Qt Quick application to use the Qt Resource system

• Easily toggle use of Qt Quick Compiler in your project

• The more binding expressions and JavaScript code, the greater the benefits of using the compiler

• Safer deployment of closed binaries, rather than collection of open and readable files.

• Qt Quick 2D renderer• Target more devices, and low-power hardware

• Qt Quick Profiler• Improve code performance

• Ensure smooth animations at all time

• Qt Quick Compiler• Shorter application start up time

• Faster application execution

• Lower application binary size

• More secure and simple-to-deployable binaries

Conclusions

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www.qt.ionils.roscher-nielsen@theqtcompany.com

Thank You!