So summing up some random development notes here:
- Harmattan version of the game utilizes Qt-components for portrait main window and for disabling swipe while playing. Symbian version does not use Qt-components as pure QML was enough.
- It's good to use Loader for separating rest of the UI from initial "splash screen" for faster startup. Another option on Harmattan would be to show static splash screen image with invoker.
- In this game, loaders are also used for help and high score views. As these are not often used, it is better to save memory and only load them when needed. Loading is fast enough not to cause notable delay.
- ShaderEffectItem is available on Harmattan, Belle and Anna+Qt 4.7.4, so it's possible to target quite a many devices. Exception is Nokia 500 which is lacking GPU for OpenGL.
- With Symbian, setting QGLWidget for viewport is required to be able to use ShaderEffectItem. On Harmattan this is not needed as the default graphics system is already set to use OpenGL.
- When application is minimized, unload ShaderEffectItems or set their 'visible' property to false. Not doing this causes minimized application to use resources unnecessarily. Application state can be tracked with Qt.application.active
- When writing shaders, be careful to keep them performing well. Symbian devices and especially newer Belle ones can handle heavy fragment shaders better than N9. As an example, moving night effect math from fragment shader to vertex shader improved performance notably on N9.
- Avoid too many ShaderEffectItems to save resources. As an example, instead of each bug containing its own burning effect, there are three global effect items in a queue, positioned and animated when needed. If three simultaneously burning bugs are not enough, it's easy to add more effect items into queue.
- QML performance notes give good general guidelines what to avoid. Qt5 version of this document is even better and provides also information on how Qt5 scenegraph and V8 engine changes reflect to optimizing QML performance.
P.S. I joined Nokia ~month ago which may increase my bias towards Qt... But it's not like I wouldn't have made my opinion pretty clear already ;-)