The document discusses the use of V-Play and Qt for responsive mobile app development, emphasizing the importance of shared code across different platforms and devices. It highlights techniques for achieving a native user experience, managing density independence, and improving user retention through features like push notifications and user-generated content. Additionally, it covers a variety of tools and resources available for developers to enhance their apps and games.

1. Qt World Summit Berlin 2015
7.10.2015
by Christian Feldbacher, MSc
Co-Founder V-Play GmbH
Qt Responsive Design
&
How to Boost User Retention
(Tech Talk)

2. cross-platform 2D game development in days
import VPlay 2.0

3. V-Play Game Engine

4. Same Code, Multiple Screen Sizes

5. V-Play App Engine / V-Play Apps
Now available on www.v-play.net/apps
the easiest to use mobile app development framework
Powered by
import VPlayApps 1.0

6. Part 1: Responsive Design with
Qt & V-Play Apps

7. Goal: Native User Experience

8. Screen Sizes, Portrait / Landscape

9. Goal: Shared Code
iOS Android
QML & JavaScript
C++
…

10. Android
Goal: Shared Code
C++
…iOS
QML & JavaScript

11. Fixed Ratio, Percentage

12. • Use multiplication for sizes
• Use Image.PreserveAspectFit
• Use font.pixelSize * height for Text
• Useful for apps that shall/can have the
same UI ratio on all devices
• Simple to implement
Fixed Ratio, Percentage

13. • Will look OK on most devices, but sizes
are not „native“ UX
• Landscape & Portrait not both
supportable
• Ugly syntax: dependent on the height of
parent items
• Hard to change: all sizes depend on
parent height
Problems with Fixed Ratio

14. • Items shall be same physical size
(millimeters) across all devices
• Pixels not usable
• Use dp instead – how to do that in QML?
Density-Independence

15. Calculate screenDpi
Example screenDpi values are:
– 326 for iPhone Retina
– 212 for Nexus 7
– 143 for 13“ fullHd notebook
Density-Independence

16. At a 160 dpi screen, 1 dp = 1 pixel
At a 320 dpi screen, 1 dp = 2 pixels
Still the same physical space!
Implementation Guide & Usage:
Density-Independence

17. Remaining DPI Tasks:
• Read system font size settings
• Provide additional scaling constants
– for PC
– Custom user scale settings possible (both sp and dp)
 Implemented in V-Play already!
Text Sizes

18. • Problem with 1 image:
– Low res image: blurs at upscaling
– High res image: space & memory waste,
performance issues at loading time
• Solution: Choose image based on screen
size or dpi
• Bad Approach:
Dynamic Image Switching

19. • File access generalized across platforms
• Works behind the scenes
• V-Play Approach:
 Less code & easier to read (no ifdefs)
 Same physical size thanks to dp()
Dynamic Image Switching
+hd2/imageSwitching.png
+hd/imageSwitching.png
imageSwitching.png

20. • Also use per platform, e.g. +ios, +android
• Together with QML Singletons set font
sizes, dimensions, layouts
• Disadvantages File Selectors:
– Must be set before QmlEngine.load()
– Cannot be changed at runtime
 to do that, use Loader
– Not as mature as Android (e.g. sw600dp)
File Selectors

21. • To achieve this:
Density-Independence Summary

22. • Use Fixed Ratio when possible:
– Pixel values based on parent.height ratio
– Easiest & fastest to develop & test
– File Selectors are auto-supported by V-Play
– Mostly in Games, not well suited for mobile
apps!
• If(FixedRatio !== possible):
– For equal physical Item sizes use dp()
– For Text use font.pixelSize: sp()
• Supply sd (default), +hd, +hd2 graphics
• Never use pixels!
QML Responsive Design Summary

23. Portrait & Landscape

24. Portrait & Landscape Code

25. Android vs. iOS

26. • Page Transitions
• List Views
• Dialogs
• Input
• Controls
• Fonts
• Default Sizes
Android vs. iOS

27. iOS vs. Android Navigation

28. Navigation Component

29. Platform Changing at Runtime

30. Showcase App Live Demo

31. • Messaging App like Facebook: 140 loc
• Twitter App: 840 loc
• Weather App: 150 loc
• Widgets: 330 loc
Lines of Code
No platform-specific application code!

32. „Qt 5 Showcases by V-Play Apps“
www.v-play.net/showcase-app
Open Source with all App Samples in V-Play SDK
For Windows, Mac, Linux, iOS, Android, Win Phone

33. • Powerful Animations, User Interfaces with Qt Quick
• Very few lines of Code
• Build on proven tech: C++, JavaScript
• Native Performance
• Easy & clean to integrate Scripting (QML) with C++
V-Play Apps
• Native UX across platforms, single code base
• Mobile First! (iOS, Android)
• Auto Adapting UI Elements (Master/Detail View)
• Density Independence
• Advanced Lists (Pull-to-refresh, Scroll Indicator,
VisibilityRefresh), Page Transitions, …
Strengths of Qt & V-Play Apps

34. Part 2: How to Increase User Retention
Of mobile apps & games

35. Push Notifications

36. V-Play Plugins
Available on www.plugins.v-play.net
Samples on GitHub & in V-Play SDK

37. • Provide content worth sharing
– Success moments in your app/game
– User Image Upload
– User Generated Content
• Share in-app and via
Social Networks

38. User-Generated Content

39. V-Play Sample Launcher
v-play.net/samples

40. User-Generated Content

41. User-Generated Content

42. User-Generated Content

43. V-Play Level Editor & Level Sharing
Squaby Particle Editor
• Save time in internal development
• Let users create levels
• Social Sharing & Rating of Levels  Community
• Monetize content packs with In-App Purchases
• Customizable Look
Add app store for user generated content to your
own apps/games easily.
Examples (in App Stores):
Stack And Friends

44. • Achievement & Leaderboard integration
in 60 Lines of Code! Also useful for apps!
V-Play Game Network

45. V-Play Game Network

46. V-Play Game Network

47. • GameCenter on steroids made for/with Qt
• True cross-platform:
– Leaderboards
– Achievements
– Cloud storage & syncing
• Deep Facebook connection
• Full offline support
• Skinnable
• Add Gamification also for
„normal apps“
V-Play Game Network

48. • Embed in your app/game
• Chat
• Smart Matchmaking: Friends, ELO Ranking
• Real-time & turn-based
Chat / Multiplayer
In-App Chat Matchmaking

49. Multiplayer Game Template

50. Retention Measurement

51. Google Analytics Integration

52. • Push Notifications
• Social Integrations like Facebook
• User-Generated Content
• Gamification elements:
– Leaderboards
– Achievements
– Multiplayer & In-App Chat
 Measure with Analytics from Day 1!
User Retention Summary

53. Final Slide 
Meet us outside @ the V-Play / Gimasi Booth!
We will show you Qt games & apps that shine 
www.v-play.net/apps
www.v-play.net

54. • V-Play Apps: http://v-play.net/apps
• V-Play Resources about Level Editor & User-Generated Content:
http://v-play.net/level-editor
• Android Guide – „Supporting Multiple Screens“:
http://developer.android.com/guide/practices/screens_support.html
• V-Play Guide - „How to create mobile games for different screen sizes and resolutions”:
http://v-play.net/doc/vplay-different-screen-sizes/
• Windows Dev Center Guide – „DPI and Device-Independent Pixels“:
http://msdn.microsoft.com/en-us/library/windows/desktop/ff684173%28v=vs.85%29.aspx
• V-Play Tutorial - „How to increase player retention & downloads in 10 minutes”:
http://v-play.net/doc/lesson-5/
• V-Play Tutorial – „How to add Facebook & Game Center sharing to your game”:
http://v-play.net/doc/lesson-6/
• V-Play Tutorial – „How to boost level creation and balancing of your game with V-Play
Level Editor”:
http://v-play.net/doc/lesson-7/
• V-Play Tutorial – „How to benefit from user-generated content in your game with V-Play
Level Store”:
http://v-play.net/doc/lesson-8/
References