Creating Energy Efficient Apps Using Qt - Revision history

Hamishwillee: Text replace - "`" to ""`


2012-10-11T01:16:30Z
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  The ''accelerometer'' and ''animations'' examples illustrate how an application can be suspended when the app window receives a {{icode|QEvent::WindowDeactivate}} event. They also contain (commented out) code to show how an app is restarted when it is moved to the foreground and receives the {{icode|QEvent::WindowActivate}} event. This section of code from the ''animations'' example shows how these events are handled:   The ''accelerometer'' and ''animations'' examples illustrate how an application can be suspended when the app window receives a {{icode|QEvent::WindowDeactivate}} event. They also contain (commented out) code to show how an app is restarted when it is moved to the foreground and receives the {{icode|QEvent::WindowActivate}} event. This section of code from the ''animations'' example shows how these events are handled:
− <code cpp>// The first show event will start the animation. + <code cpp-qt>// The first show event will start the animation.
  case QEvent::Show:   case QEvent::Show:
  // Tap the screen to restart the animation.   // Tap the screen to restart the animation.
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  The ''accelerometer'' example app includes a slightly contrived illustration of this principal. The accelerometer does not provide a signal when its state changes, so a timer is used to check whether the device has been moved. However, if the user has put the device down there is no need to continually poll for accelerometer data, as there won’t be any. So the example uses two timers, one to check for changes in the accelerometer data and another to kill this timer (and close the connection to the sensor) if the device appears stationary for a relatively long period. Setting this “inactivity” timer is shown below:   The ''accelerometer'' example app includes a slightly contrived illustration of this principal. The accelerometer does not provide a signal when its state changes, so a timer is used to check whether the device has been moved. However, if the user has put the device down there is no need to continually poll for accelerometer data, as there won’t be any. So the example uses two timers, one to check for changes in the accelerometer data and another to kill this timer (and close the connection to the sensor) if the device appears stationary for a relatively long period. Setting this “inactivity” timer is shown below:
− <code cpp> + <code cpp-qt>
  QAccelerometerReading *reading = accelerometer->reading();   QAccelerometerReading *reading = accelerometer->reading();
  qreal xacceleration = 0.0f;   qreal xacceleration = 0.0f;
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  In the ''accelerometer'' example the accelerometer is started when the app first starts or when the screen is tapped (after the accelerometer has stopped) and the code can be modified to automatically restart when the app comes to the foreground as follows:   In the ''accelerometer'' example the accelerometer is started when the app first starts or when the screen is tapped (after the accelerometer has stopped) and the code can be modified to automatically restart when the app comes to the foreground as follows:
− <code cpp>bool View::event(QEvent *event) + <code cpp-qt>bool View::event(QEvent *event)
  {   {
       switch (event->type()) {        switch (event->type()) {
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  ** Use {{icode|const}} iterators where elements are not modified.     ** Use {{icode|const}} iterators where elements are not modified.  
  *:Consider the two code fragments below. In both examples the code iterates from the beginning to the end of the vector and assigns the value of {{icode|qreal}} to either {{icode|foo}} or {{icode|bar}}. The first fragment uses a non-const iterator as follows:   *:Consider the two code fragments below. In both examples the code iterates from the beginning to the end of the vector and assigns the value of {{icode|qreal}} to either {{icode|foo}} or {{icode|bar}}. The first fragment uses a non-const iterator as follows:
− *:<code cpp>QVector<qreal>::iterator it = container.begin(); + *:<code cpp-qt>QVector<qreal>::iterator it = container.begin();
  while (it != container.end()) {   while (it != container.end()) {
       foo += *it;        foo += *it;
       ++it;}</code>        ++it;}</code>
  *:The second method uses a const iterator:   *:The second method uses a const iterator:
− *:<code cpp>QVector<qreal>::const_iterator it = container.constBegin(); + *:<code cpp-qt>QVector<qreal>::const_iterator it = container.constBegin();
  while (it != container.constEnd()) {   while (it != container.constEnd()) {
       bar += *it;        bar += *it;



Hamishwillee: Hamishwillee - Bot update - Add ArticleMetaData
2012-07-25T01:48:35Z
Hamishwillee - Bot update - Add ArticleMetaData

			
			
			
			
		
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  [[Category:Qt]][[Category:Symbian]][[Category:Power Management]]   [[Category:Qt]][[Category:Symbian]][[Category:Power Management]]
  {{Abstract|This article is designed to help developers create power efficient Qt code for use on Symbian devices. }}   {{Abstract|This article is designed to help developers create power efficient Qt code for use on Symbian devices. }}
− {{ArticleMetaData + {{ArticleMetaData <!-- v1.2 -->
− |sourcecode=<br />[[Media:Energy_Qt_iteration.zip]]<br />[[Media:Energy_Qt_animations.zip]]<br />[[Media:Energy_Qt_accelerometer.zip]] + |sourcecode= <br />[[Media:Energy Qt iteration.zip]]<br />[[Media:Energy Qt animations.zip]]<br />[[Media:Energy Qt accelerometer.zip]]
  |installfile= <!-- Link to installation file (e.g. [[Media:The Installation File.sis]]) -->   |installfile= <!-- Link to installation file (e.g. [[Media:The Installation File.sis]]) -->
  |devices= <!-- Devices tested against - e.g. ''devices=N95, N8'') -->   |devices= <!-- Devices tested against - e.g. ''devices=N95, N8'') -->
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  |platform= <!-- Compatible platforms - e.g. Symbian^1 and later, Qt 4.6 and later -->   |platform= <!-- Compatible platforms - e.g. Symbian^1 and later, Qt 4.6 and later -->
  |devicecompatability= <!-- Compatible devices e.g.: All* (must have internal GPS) -->   |devicecompatability= <!-- Compatible devices e.g.: All* (must have internal GPS) -->
− |signing=<!-- Signing requirements - empty or one of: Self-Signed, DevCert, Manufacturer --> + |dependencies= <!-- Any other/external dependencies e.g.: Google Maps Api v1.0 -->
− |capabilities=<!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. --> + |signing= <!-- Signing requirements - empty or one of: Self-Signed, DevCert, Manufacturer -->
− |keywords=Energy Efficiency + |capabilities= <!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->
  + |keywords= Energy Efficiency
  + |language= <!-- Language category code for non-English topics - e.g. Lang-Chinese -->
  + |translated-by= <!-- [[User:XXXX]] -->
  + |translated-from-title= <!-- Title only -->
  + |translated-from-id= <!-- Id of translated revision -->
  + |review-by= <!-- After re-review: [[User:username]] -->
  + |review-timestamp= <!-- After re-review: YYYYMMDD -->
  + |update-by= <!-- After significant update: [[User:username]]-->
  + |update-timestamp= <!-- After significant update: YYYYMMDD -->
  |creationdate= 20100601 <!-- Guess -->   |creationdate= 20100601 <!-- Guess -->
− |author=[[User:rebloor]]   + |author= [[User:rebloor]]
  }}   }}
  == Introduction ==   == Introduction ==
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  </code>   </code>
    
− [[File:Energy_Qt_Animation.png|frame|none|The "animations" example, showing the animation stopped as a result of opening the task switcher.]] + [[File:Energy Qt Animation.png|frame|none|The "animations" example, showing the animation stopped as a result of opening the task switcher.]]
  In the example, processing is stopped by halting the timer used to trigger the updating of the balls' positions (and in the "accelerometer" example, to obtain the accelerometer values). Because the position of the ball is no longer updated the {{icode|QGraphicsScene}} object stops painting to the screen as there are no changes to paint. As a result, all significant processing in the application stops.   In the example, processing is stopped by halting the timer used to trigger the updating of the balls' positions (and in the "accelerometer" example, to obtain the accelerometer values). Because the position of the ball is no longer updated the {{icode|QGraphicsScene}} object stops painting to the screen as there are no changes to paint. As a result, all significant processing in the application stops.
  The effect is illustrated below. On the left is a profile of the energy consumption (obtained with [[#Nokia Energy Profiler|Nokia Energy Profiler]]) of a version of “accelerometer” without the stop code — so it continues to run and update the screen even when the device is locked. Compare this with the example version that stops drawing when the device is locked. The “without stop” version reduces its power consumption by about half when the device is locked (because the screen is no longer lit) whereas the “with stop” version reverts to standby power consumption.     The effect is illustrated below. On the left is a profile of the energy consumption (obtained with [[#Nokia Energy Profiler|Nokia Energy Profiler]]) of a version of “accelerometer” without the stop code — so it continues to run and update the screen even when the device is locked. Compare this with the example version that stops drawing when the device is locked. The “without stop” version reduces its power consumption by about half when the device is locked (because the screen is no longer lit) whereas the “with stop” version reverts to standby power consumption.  
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  |73 ms   |73 ms
  |}   |}
− ::[[File:Energy_Qt_Iteration.png|frame|none|The "iteration" example application from a Nokia N97]] + ::[[File:Energy Qt Iteration.png|frame|none|The "iteration" example application from a Nokia N97]]
    
  * Avoid instantiating overly large objects — amazingly, examples have been seen of developers trying to instantiate items such as images containing a trillion (10<sup>12</sup>) pixels each with 32-bit colour depth. Such objects require a lot of processing!   * Avoid instantiating overly large objects — amazingly, examples have been seen of developers trying to instantiate items such as images containing a trillion (10<sup>12</sup>) pixels each with 32-bit colour depth. Such objects require a lot of processing!
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  ==== Nokia Energy Profiler ====   ==== Nokia Energy Profiler ====
− The Nokia Energy Profiler is the most accessible tool for testing an application’s energy usage. In fact it’s delivered as a consumer application through [http://store.ovi.com/content/17374 Ovi Store]. Usable on most Nokia S60 3rd Edition, Feature Pack 1 and later devices, Nokia Energy Profiler provides information on:   + The Nokia Energy Profiler is the most accessible tool for testing an application’s energy usage. In fact it’s delivered as a consumer application through [http://store.ovi.com/content/17374 Nokia Store]. Usable on most Nokia S60 3rd Edition, Feature Pack 1 and later devices, Nokia Energy Profiler provides information on:  
  *Power consumption, as well as battery voltage and current.   *Power consumption, as well as battery voltage and current.
  *Cumulative power consumption.   *Cumulative power consumption.
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  * Active use power consumption testing. In this test scenario you make use of your application, exercising various different use cases, and look for any unexpected spikes in power consumption. When issues are identified, the testing use cases should be refined until the code that is causing the problem is identified.   * Active use power consumption testing. In this test scenario you make use of your application, exercising various different use cases, and look for any unexpected spikes in power consumption. When issues are identified, the testing use cases should be refined until the code that is causing the problem is identified.
    
− Nokia Energy Profiler can be downloaded to a Nokia device from [http://store.ovi.com/content/17374 Ovi Store]. + Nokia Energy Profiler can be downloaded to a Nokia device from [http://store.ovi.com/content/17374 Nokia Store].
    
  An alternative solution for this type of testing is the Performance Monitor application.   An alternative solution for this type of testing is the Performance Monitor application.
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  == Code Examples ==   == Code Examples ==
    
− * [[Media:Energy_Qt_iteration.zip]] + * [[Media:Energy Qt iteration.zip]]
− * [[Media:Energy_Qt_animations.zip]] + * [[Media:Energy Qt animations.zip]]
− * [[Media:Energy_Qt_accelerometer.zip]] + * [[Media:Energy Qt accelerometer.zip]]
    
    
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  {{Licence-SymbianFoundation-CC-BY-SA-2.0}}   {{Licence-SymbianFoundation-CC-BY-SA-2.0}}
  + [[Category:Code Examples]]



Hamishwillee: Hamishwillee - Delete link to discussion that is no longer available
2011-08-24T07:24:18Z
Hamishwillee - Delete link to discussion that is no longer available

			
			
			
			
		
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  Polling consumes CPU cycles and battery life whether or not a change has occurred, and can results in a delayed reaction depending on the frequency of the polling cycle. More importantly, polling timers may prevent the device from entering its low-power or sleep mode. The event-driven paradigm overcomes the drawbacks of polling. In this paradigm, an event signal is issued only when something changes. The application threads are dormant while waiting for the signal. If all of the code in the system is dormant and waiting for some event, the device can enter its low power mode.   Polling consumes CPU cycles and battery life whether or not a change has occurred, and can results in a delayed reaction depending on the frequency of the polling cycle. More importantly, polling timers may prevent the device from entering its low-power or sleep mode. The event-driven paradigm overcomes the drawbacks of polling. In this paradigm, an event signal is issued only when something changes. The application threads are dormant while waiting for the signal. If all of the code in the system is dormant and waiting for some event, the device can enter its low power mode.
    
− Fortunately the architecture of Qt is fundamentally event driven and you can find more information on the signalling mechanism in the Qt article on [http://doc.qt.nokia.com/stable/signalsandslots.html signals and slots]. For a general discussion on event-driven programming, see the wiki article [[Event-driven programming (Best Practices in Symbian C++ Design)]]. Qt’s event driven architecture means that by following good Qt programming practices you should end up making use of event signals where they are available. + Fortunately the architecture of Qt is fundamentally event driven and you can find more information on the signalling mechanism in the Qt article on [http://doc.qt.nokia.com/stable/signalsandslots.html signals and slots]. Qt’s event driven architecture means that by following good Qt programming practices you should end up making use of event signals where they are available.
    
  There are many circumstances where timers are the most practical solution to design requirements. The key point here is not that you can't use timers, but that you ensure that timers are stopped when the application is in the background or there has been a period of user inactivity. If all the application is doing is waiting for timers to expire, then this will prevent the device going into a low power mode.   There are many circumstances where timers are the most practical solution to design requirements. The key point here is not that you can't use timers, but that you ensure that timers are stopped when the application is in the background or there has been a period of user inactivity. If all the application is doing is waiting for timers to expire, then this will prevent the device going into a low power mode.



Hamishwillee: Hamishwillee - Remove the SF migration warning
2011-08-24T07:20:48Z
Hamishwillee - Remove the SF migration warning

			
			
			
			
		
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  [[Category:Qt]][[Category:Symbian]][[Category:Power Management]]   [[Category:Qt]][[Category:Symbian]][[Category:Power Management]]
− {{SymbianFoundationMigratedContentWarning}}  
  {{Abstract|This article is designed to help developers create power efficient Qt code for use on Symbian devices. }}   {{Abstract|This article is designed to help developers create power efficient Qt code for use on Symbian devices. }}
  {{ArticleMetaData   {{ArticleMetaData
−  
  |sourcecode=<br />[[Media:Energy_Qt_iteration.zip]]<br />[[Media:Energy_Qt_animations.zip]]<br />[[Media:Energy_Qt_accelerometer.zip]]   |sourcecode=<br />[[Media:Energy_Qt_iteration.zip]]<br />[[Media:Energy_Qt_animations.zip]]<br />[[Media:Energy_Qt_accelerometer.zip]]
  |installfile= <!-- Link to installation file (e.g. [[Media:The Installation File.sis]]) -->   |installfile= <!-- Link to installation file (e.g. [[Media:The Installation File.sis]]) -->
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  |capabilities=<!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->   |capabilities=<!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->
  |keywords=Energy Efficiency   |keywords=Energy Efficiency
− |creationdate= <!-- Format DD month, YYYY --> + |creationdate= 20100601 <!-- Guess -->
  |author=[[User:rebloor]]     |author=[[User:rebloor]]  
  }}   }}
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  To put things in perspective, the following table shows some typical power consumption requirements for key hardware components.     To put things in perspective, the following table shows some typical power consumption requirements for key hardware components.  
− {| border="1" cellspacing="0" cellpadding="5" align="center" + {| class="wikitable"
  !Hardware   !Hardware
  !Typical power consumption (mW)   !Typical power consumption (mW)
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  ::The difference between the execution time for the two methods can be quite significant, as illustrated by the table below which shows the approximate execution time of the iterator example on various devices.  The compiler is able to optimise more effectively when it’s explicitly told to access the elements using a {{icode|const}}.     ::The difference between the execution time for the two methods can be quite significant, as illustrated by the table below which shows the approximate execution time of the iterator example on various devices.  The compiler is able to optimise more effectively when it’s explicitly told to access the elements using a {{icode|const}}.  
    
− ::{| border="1" cellspacing="0" cellpadding="5" align="center" + ::{| class="wikitable"
  !Device   !Device
  !const iterator   !const iterator
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  Nokia Energy Profiler can be downloaded to a Nokia device from [http://store.ovi.com/content/17374 Ovi Store].   Nokia Energy Profiler can be downloaded to a Nokia device from [http://store.ovi.com/content/17374 Ovi Store].
    
− An alternative solution for this type of testing is the [[Performance Monitor]] application. + An alternative solution for this type of testing is the Performance Monitor application.
  +  
  ==== Carbide.c++ Performance Investigator ====   ==== Carbide.c++ Performance Investigator ====
− An option for more rigorous analysis of an application’s performance is provided by [[Performance Investigator Profiler]]. Performance Investigator (PI) has the advantage over Nokia Energy Profiler of providing explicit information on the code that is running on a device. This enables you to identify more readily the code that is causing energy consumption or other issues, such as out of memory. + An option for more rigorous analysis of an application’s performance is provided by Performance Investigator Profiler. Performance Investigator (PI) has the advantage over Nokia Energy Profiler of providing explicit information on the code that is running on a device. This enables you to identify more readily the code that is causing energy consumption or other issues, such as out of memory.
    
  PI however, is part of the Carbide.c++ toolset and requires you to install Carbide.c++ as well as a profiling client on your device. If you are using the Qt tools for development, the additional effort in using PI may be worthwhile only if you encounter problems you cannot resolve using the information provided by Nokia Energy Profiler.     PI however, is part of the Carbide.c++ toolset and requires you to install Carbide.c++ as well as a profiling client on your device. If you are using the Qt tools for development, the additional effort in using PI may be worthwhile only if you encounter problems you cannot resolve using the information provided by Nokia Energy Profiler.  
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  By following this advice you will go a long way towards ensuring your app does not get labelled as a battery eater. However, creating a power efficient app is not a precise science. Variation in hardware and user behaviour can have unexpected results. So while good design is the best starting point ultimately testing and optimisation are just as essential.   By following this advice you will go a long way towards ensuring your app does not get labelled as a battery eater. However, creating a power efficient app is not a precise science. Variation in hardware and user behaviour can have unexpected results. So while good design is the best starting point ultimately testing and optimisation are just as essential.
    
− <!-- Categories --> + {{Licence-SymbianFoundation-CC-BY-SA-2.0}}
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−  {{Licence-SymbianFoundation-CC-BY-SA-2.0}} + 



Hamishwillee: Hamishwillee - Fix redirect and layout issues
2011-08-02T06:46:10Z
Hamishwillee - Fix redirect and layout issues

			
			
			
			
		
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− [[Category:Qt]][[Category:Symbian]] + [[Category:Qt]][[Category:Symbian]][[Category:Power Management]]
  {{SymbianFoundationMigratedContentWarning}}     {{SymbianFoundationMigratedContentWarning}}  
  {{Abstract|This article is designed to help developers create power efficient Qt code for use on Symbian devices. }}   {{Abstract|This article is designed to help developers create power efficient Qt code for use on Symbian devices. }}
− {{ComesWithCode + {{ArticleMetaData
− |[[File:Energy_Qt_iteration.zip]] +  
− |[[File:Energy_Qt_animations.zip]] + |sourcecode=<br />[[Media:Energy_Qt_iteration.zip]]<br />[[Media:Energy_Qt_animations.zip]]<br />[[Media:Energy_Qt_accelerometer.zip]]
− |[[File:Energy_Qt_accelerometer.zip]]}} + |installfile= <!-- Link to installation file (e.g. [[Media:The Installation File.sis]]) -->
  + |devices= <!-- Devices tested against - e.g. ''devices=N95, N8'') -->
  + |sdk= <!-- SDK(s) built and tested against (e.g. [http://linktosdkdownload/ Nokia Qt SDK 1.1]) -->
  + |platform= <!-- Compatible platforms - e.g. Symbian^1 and later, Qt 4.6 and later -->
  + |devicecompatability= <!-- Compatible devices e.g.: All* (must have internal GPS) -->
  + |signing=<!-- Signing requirements - empty or one of: Self-Signed, DevCert, Manufacturer -->
  + |capabilities=<!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->
  + |keywords=Energy Efficiency
  + |creationdate= <!-- Format DD month, YYYY -->
  + |author=[[User:rebloor]] 
  + }}
  == Introduction ==   == Introduction ==
    
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  Mobile device broadly use two screen technologies: LCD (Liquid Crystal Display) or OLED (Organic Light Emitting Diode). LCD is the older technology, with OLED displays becoming common on higher end devices. The technology trend will probably see OLED as the prevalent technology within the next couple of years.   Mobile device broadly use two screen technologies: LCD (Liquid Crystal Display) or OLED (Organic Light Emitting Diode). LCD is the older technology, with OLED displays becoming common on higher end devices. The technology trend will probably see OLED as the prevalent technology within the next couple of years.
    
− The principal difference between the two technologies is that OLEDs create light directly while LCDs require a backlight to make them usefully visible. Because OLEDs generate light the amount of power they consume varies greatly, ratios of 1:14 have [http://blogs.forum.nokia.com/blog/long-live-your-mobile-battery/2010/06/07/color-makes-a-difference been observed] between the power consumption of a black screen compared to a white one. + The principal difference between the two technologies is that OLEDs create light directly while LCDs require a backlight to make them usefully visible. Because OLEDs generate light the amount of power they consume varies greatly, ratios of 1:14 have [http://www.developer.nokia.com/Community/Blogs/blog/long-live-your-mobile-battery/2010/06/07/color-makes-a-difference been observed] between the power consumption of a black screen compared to a white one.
    
  LCDs exhibit variations in power consumption between similar black and white screens, however the variation is closer to 1:2.   LCDs exhibit variations in power consumption between similar black and white screens, however the variation is closer to 1:2.
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  [[Symbian C++ Performance Tips]] — This Symbian wiki article provides tips on coding for app performance in Symbian C++. These tips don’t directly relate to power efficient coding, however, in general more efficient code will require less CPU cycles and therefore less power to execute. Many of the tips are general in nature and the principles discussed can be applied to Qt coding.   [[Symbian C++ Performance Tips]] — This Symbian wiki article provides tips on coding for app performance in Symbian C++. These tips don’t directly relate to power efficient coding, however, in general more efficient code will require less CPU cycles and therefore less power to execute. Many of the tips are general in nature and the principles discussed can be applied to Qt coding.
  + 
  + == Code Examples ==
  + 
  + * [[Media:Energy_Qt_iteration.zip]]
  + * [[Media:Energy_Qt_animations.zip]]
  + * [[Media:Energy_Qt_accelerometer.zip]]
  + 
    
  ==Conclusion==   ==Conclusion==



Hamishwillee: Automated change of text from {{SymbianFoundationLicence}} to {{Licence-SymbianFoundation-CC-BY-SA-2.0}}. (Use more descriptive license template name)
2011-06-13T06:56:55Z
Automated change of text from {{SymbianFoundationLicence}} to {{Licence-SymbianFoundation-CC-BY-SA-2.0}}. (Use more descriptive license template name)

			
			
			
			
		
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Kiran10182 at 11:32, 30 May 2011
2011-05-30T11:32:30Z


			
			
			
			
		
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  The Qt documentation also includes information on functions that are inherently slow, for example {{icode|QWidget::setMask}} which can be slow if the masked region is particularly complex.   The Qt documentation also includes information on functions that are inherently slow, for example {{icode|QWidget::setMask}} which can be slow if the masked region is particularly complex.
  There are also a number of books on Qt development that provide invaluable insight into the best ways to code in Qt. Of these we would recommend:   There are also a number of books on Qt development that provide invaluable insight into the best ways to code in Qt. Of these we would recommend:
− * [http://developer.qt.nokia.com/bookscpp-gui-programming-with-qt-4-2nd-edition C++ GUI Programming with Qt 4 (2nd Edition) - The official C++/Qt book], by Jasmin Blanchette and Mark Summerfield. + * [http://developer.qt.nokia.com/books/view/c_gui_programming_with_qt_4_2nd_edition_the_official_c_qt_book C++ GUI Programming with Qt 4 (2nd Edition) - The official C++/Qt book], by Jasmin Blanchette and Mark Summerfield.
− * [http://developer.qt.nokia.com/booksfoundations-of-qt-development Foundations of Qt Development], by Johan Thelin + * [http://developer.qt.nokia.com/books/view/foundations_of_qt_development Foundations of Qt Development], by Johan Thelin
  You can find a longer, regularly maintained list of books on Qt [http://developer.qt.nokia.com/books here].   You can find a longer, regularly maintained list of books on Qt [http://developer.qt.nokia.com/books here].
    



Hamishwillee: Bot fixing redirect link
2011-05-27T05:31:03Z
Bot fixing redirect link

			
			
			
			
		
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  In summary, use events where they are available and if you use timers, kill them when they no longer serve a useful purpose.   In summary, use events where they are available and if you use timers, kill them when they no longer serve a useful purpose.
    
− If you wish to make use of timers the blog post [http://labs.trolltech.com/blogs/2010/07/13/when-being-wrong-is-right/ When being wrong is right] is well worth a read, to be aware of some improvements expected in Qt 4.8. + If you wish to make use of timers the blog post [http://labs.qt.nokia.com/2010/07/13/when-being-wrong-is-right/ When being wrong is right] is well worth a read, to be aware of some improvements expected in Qt 4.8.
    
  === Optimise your use of graphic content and effects ===   === Optimise your use of graphic content and effects ===
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  ===== Understand how Qt draws graphics =====   ===== Understand how Qt draws graphics =====
    
− The first step to creating efficient graphics in Qt is, rather obviously, understanding how Qt handles graphics. An excellent discussion of graphics in Qt is provided by [http://labs.trolltech.com/blogs/author/gunnar/ Gunnar Sletta’s blog] series, which comprises: + The first step to creating efficient graphics in Qt is, rather obviously, understanding how Qt handles graphics. An excellent discussion of graphics in Qt is provided by [http://labs.qt.nokia.com/author/gunnar/ Gunnar Sletta’s blog] series, which comprises:
− * [http://labs.trolltech.com/blogs/2009/12/14/qt-graphics-and-performance-whats-hot-and-whats-not/ Qt Graphics and Performance - Whats Hot and whats Not]   + * [http://labs.qt.nokia.com/2009/12/14/qt-graphics-and-performance-whats-hot-and-whats-not/ Qt Graphics and Performance - Whats Hot and whats Not]  
− * [http://labs.trolltech.com/blogs/2009/12/16/qt-graphics-and-performance-an-overview/ Qt Graphics and Performance - An Overview] + * [http://labs.qt.nokia.com/2009/12/16/qt-graphics-and-performance-an-overview/ Qt Graphics and Performance - An Overview]
− * [http://labs.trolltech.com/blogs/2009/12/18/qt-graphics-and-performance-the-raster-engine/ Qt Graphics and Performance - The Raster Engine] + * [http://labs.qt.nokia.com/2009/12/18/qt-graphics-and-performance-the-raster-engine/ Qt Graphics and Performance - The Raster Engine]
− * [http://labs.trolltech.com/blogs/2010/01/11/qt-graphics-and-performance-the-cost-of-convenience/ Qt Graphics and Performance - The Cost of Convenience] + * [http://labs.qt.nokia.com/2010/01/11/qt-graphics-and-performance-the-cost-of-convenience/ Qt Graphics and Performance - The Cost of Convenience]
− * [http://labs.trolltech.com/blogs/2010/01/18/qt-graphics-and-performance-fast-text/ Qt Graphics and Performance - Fast Text] + * [http://labs.qt.nokia.com/2010/01/18/qt-graphics-and-performance-fast-text/ Qt Graphics and Performance - Fast Text]
− * [http://labs.trolltech.com/blogs/2010/01/21/qt-graphics-and-performance-generating-content-in-threads/ Qt Graphics and Performance - Generating Content in Threads]. + * [http://labs.qt.nokia.com/2010/01/21/qt-graphics-and-performance-generating-content-in-threads/ Qt Graphics and Performance - Generating Content in Threads].
    
  ===== Make the best use of hardware accelerated graphics =====   ===== Make the best use of hardware accelerated graphics =====
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  Some typical examples include:   Some typical examples include:
  * Traverse lists and access list items appropriately:   * Traverse lists and access list items appropriately:
− ** Prefer the most power efficient iterator — Qt provides several different methods for traversing a list, such as STL style iterators and a {{icode|foreach}} macro. However, the performance of the {{icode|foreach}} macro can be significantly [http://labs.trolltech.com/blogs/2009/01/23/iterating-efficiently/ slower than other methods]. + ** Prefer the most power efficient iterator — Qt provides several different methods for traversing a list, such as STL style iterators and a {{icode|foreach}} macro. However, the performance of the {{icode|foreach}} macro can be significantly [http://labs.qt.nokia.com/2009/01/23/iterating-efficiently/ slower than other methods].
  ** Prefer {{Qapiname|QList::at()}} for read-only access to list items. Using {{icode|at()}} can be faster than [http://doc.qt.nokia.com/stable/qlist.html#operator-5b-5d QList::operator &#91;&#93;], because it does not cause a deep copy (duplication of the list data) to occur.   ** Prefer {{Qapiname|QList::at()}} for read-only access to list items. Using {{icode|at()}} can be faster than [http://doc.qt.nokia.com/stable/qlist.html#operator-5b-5d QList::operator &#91;&#93;], because it does not cause a deep copy (duplication of the list data) to occur.
  ** Use {{icode|const}} iterators where elements are not modified.     ** Use {{icode|const}} iterators where elements are not modified.  
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  * [http://developer.qt.nokia.com/ Qt Developer Network] — at the time of writing (July 2010) this resources is still in beta, however it should be a valuable source of information on Qt development.   * [http://developer.qt.nokia.com/ Qt Developer Network] — at the time of writing (July 2010) this resources is still in beta, however it should be a valuable source of information on Qt development.
  * The [http://doc.qt.nokia.com/qq/ Qt Quarterly] — this publication, containing high-quality technical articles written by Qt experts, is designed to give developers added insight into Qt programming.   * The [http://doc.qt.nokia.com/qq/ Qt Quarterly] — this publication, containing high-quality technical articles written by Qt experts, is designed to give developers added insight into Qt programming.
− * [http://labs.trolltech.com/blogs/ Qt Labs blog] — regular blogs from the experts within Qt. In addition to general information on developments in the Qt framework, articles often offer insight into good programming techniques. + * [http://labs.qt.nokia.com/ Qt Labs blog] — regular blogs from the experts within Qt. In addition to general information on developments in the Qt framework, articles often offer insight into good programming techniques.
  The Qt documentation also includes information on functions that are inherently slow, for example {{icode|QWidget::setMask}} which can be slow if the masked region is particularly complex.   The Qt documentation also includes information on functions that are inherently slow, for example {{icode|QWidget::setMask}} which can be slow if the masked region is particularly complex.
  There are also a number of books on Qt development that provide invaluable insight into the best ways to code in Qt. Of these we would recommend:   There are also a number of books on Qt development that provide invaluable insight into the best ways to code in Qt. Of these we would recommend:
− * [http://qt.nokia.com/developer/books/cpp-gui-programming-with-qt-4-2nd-edition C++ GUI Programming with Qt 4 (2nd Edition) - The official C++/Qt book], by Jasmin Blanchette and Mark Summerfield. + * [http://developer.qt.nokia.com/bookscpp-gui-programming-with-qt-4-2nd-edition C++ GUI Programming with Qt 4 (2nd Edition) - The official C++/Qt book], by Jasmin Blanchette and Mark Summerfield.
− * [http://qt.nokia.com/developer/books/foundations-of-qt-development Foundations of Qt Development], by Johan Thelin + * [http://developer.qt.nokia.com/booksfoundations-of-qt-development Foundations of Qt Development], by Johan Thelin
− You can find a longer, regularly maintained list of books on Qt [http://qt.nokia.com/developer/books/ here]. + You can find a longer, regularly maintained list of books on Qt [http://developer.qt.nokia.com/books here].
    
  ====File access====   ====File access====
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  ==== Other options ====   ==== Other options ====
− Performance investigation can be undertaken with tools such as the [http://www.arm.com/products/tools/arm-profiler.php Arm Profiler], however these tools generally need specific hardware or development boards to enable their use. + Performance investigation can be undertaken with tools such as the [http://www.arm.com/products/tools/software-tools/rvds/arm-profiler.php Arm Profiler], however these tools generally need specific hardware or development boards to enable their use.
    
  == Other sources of information ==   == Other sources of information ==



Hamishwillee: Fix up some broken links. Add abstract
2011-04-28T01:22:53Z
Fix up some broken links. Add abstract
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Hamishwillee at 10:24, 4 April 2011
2011-04-04T10:24:35Z


			
			
			
			
		
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  {{SymbianFoundationMigratedContentWarning}}     {{SymbianFoundationMigratedContentWarning}}  
  This article is designed to help developers create power efficient Qt code for use on Symbian devices.     This article is designed to help developers create power efficient Qt code for use on Symbian devices.

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Creating Energy Efficient Apps Using Qt - Revision history

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