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=liqbase :: the core library=
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==liqbase :: the core library==
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'''Note, this document describes a library which is not currently available, however its precursor [[liqbase]] is available for download:'''
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'''http://maemo.org/downloads/product/OS2008/liqbase/.'''
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The formatting here is rubbish and I dunno how to fix it.
This is preliminary outline documentation for my library and toolkit.
This is preliminary outline documentation for my library and toolkit.
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it will be expanded upon over the coming days.
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it will be expanded upon over the coming days
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===Rationale===
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'''Note, this describes a library which is not currently available, however its precursor [[liqbase]] is available.'''
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liqbase was born of frustration.
 
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It started out as a collection of ideas and principles which show off the nokia internet tablet as a fast versatile handheld computer which very rapidly grew into a large monolithic application.
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liqbase started out as a collection of applications which show off the nokia internet tablet as a fast versatile handheld computer.
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It was the first application I have written in C in many years was and used by myself to learn about the various libraries and interactions on the nokia internet tablets.
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A proof of concept so to speak.
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It was the first application I have written in C in many years has been used to learn about the device and the various libraries and interactions on the Nokia internet tablets.
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The library is aimed to correct the mistakes I made with the monolithic application and to provide a framework to continue building my applications.
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A proof of concept so to speak.
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The library is aimed to correct the mistakes I made and to provide a framework to continue building my shiny applications.
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It has been designed to make it as easy as possible to produce high performance touch sensitive applications.
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The applications are resolution independent and capable of operating at high speed with low cpu overheads.
It contains a small set of classes which are usable for creating rich touchable GUI components.
It contains a small set of classes which are usable for creating rich touchable GUI components.
It has been written in C for both speed and expandability.
It has been written in C for both speed and expandability.
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At present it is very specifically focused upon the Nokia internet tablet computers though it is compilable and usable within x86 linux as well.
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At present it is very specifically focused upon the Nokia internet tablet computers running linux.
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===Why not GTK+ or Qt?===
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it makes use of the following libraries:  
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I looked carefully at GTK+ when I first got my tablet and would have been happy it if it had the required performance, it has (semi) sane construction methods and an expansive library of controls and utility functions.
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However on the tablet graphical performance was so poor that anything I attempted felt slow and applications crawled along. Qt had its own problems and still is not a viable option on the devices.
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I wanted to do things which I took for granted on my old PDA and have done for years in Visual Basic and found the existing toolkits lacking.
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===Dependencies===
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liqbase makes use of the following libraries:  
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*X11 window manager for the events.
*X11 window manager for the events.
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*xsp for the pressure sensitive mouse input
*xsp for the pressure sensitive mouse input
*ttflib ttf font handling
*ttflib ttf font handling
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*libpng for reading and writing image data
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*libpng
*libjpeg
*libjpeg
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*sqlite3 for the database manipulation
 
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graphics are rendered using the XV library using the YUV video format. This is a lower bandwidth video mode which has full resolution Luma, but half resolution Chroma.
 
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===Base Classes===
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graphics are rendered using the XV library using the YUV video format.
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This is a lower bandwidth video mode which has full resolution Luma, but half resolution Chroma.
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It is being constructed around a core set of interrelated classes
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It is being constructed around a set of interrelated classes
*liqapp core system functions
*liqapp core system functions
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*liqgraph a special resolution independent graphics interface which a cell uses
*liqgraph a special resolution independent graphics interface which a cell uses
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With these classes I will be able to construct the applications started inside liqbase.
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With these classes I will be able to construct the applications started inside liqbase
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The classes outlined here existed in some form or other in the old liqbase and I have not yet documented the descendants of the cell class which sit together to form the UI itself.
 
   
   
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===system class structure===
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==class structure==
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The system classes created in liqbase follow the same object pattern and contain the following default standard methods:
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<source lang="c">
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Most classes created in liqbase follow the same object pattern and contain the following default standard methods:
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<PRE>
class *class_new()
class *class_new()
{
{
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// call _release on all members of this class
// call _release on all members of this class
}
}
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</source>
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</PRE>
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The reference counting is held as a private member inside the instance itself.
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User classes and instances built from cells do not require this interface.
 
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The reference counting is held as a private member inside the instance itself.
 
There is no concept of inheritance at this level, however once you have instances of cell classes (described in detail below) they follow generic inheritance rules and can expand.
There is no concept of inheritance at this level, however once you have instances of cell classes (described in detail below) they follow generic inheritance rules and can expand.
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===Example cell lifespan===
 
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A usual cycle goes something like this
 
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<source lang="c">
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==Example Cell construction==
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A usual cycle goes like this
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<PRE>
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void hello_world()
void hello_world()
{
{
     liqcell * myform = liqcell_newwidget(“myform”,”form”, 340, 60);
     liqcell * myform = liqcell_newwidget(“myform”,”form”, 340, 60);
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     liqcell *l1 = liqcell_newwidget(“hello”,”label”, 60, 60);
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     liqcell *l1 = liqcell_newwidget(“hello”,”label”, 60, 60);
     liqcell *l2 = liqcell_newwidget(“world”,” label”, 60, 60);
     liqcell *l2 = liqcell_newwidget(“world”,” label”, 60, 60);
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     liqcell_release(myform);
     liqcell_release(myform);
}
}
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</source>
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</PRE>
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===Cell inheritance===
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The cell class provides a basic unit which everything is built up from. When used in a visual context, it represents a rectangular area on the screen. A cell can also be used as a simple  property holding information intended for its parent. Each cell can hold references to a font, an image and a sketch or even another cell. It can be inherited from other cells which expand its utility and purpose.
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===Dynamic scaling===
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liqbase is designed to operate in a truly resolution independent manner, after designing a widget according to specifications, it does not matter whether it is run on a lower or higher resolution display as the content will render correctly.
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I have taken special care ensuring the font class operates as expected within a dynamic resolution independent environment. At design time, the operator configures a form to certain dimensions (at 225dpi) and configures font sizes and positions relative to this. The fonts make use of extensive dynamic caching to both improve loading speed and to ensure that the correct glyph is displayed at the correct size as required.  The slight drawback with this approach is that at different scales there is some very slight variation in the exact final font size due to integer only glyph widths.
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At runtime, the entire screen is situated within the available boundary and rendered accordingly. A landscape layout will run correctly in portrait mode, however it will be displayed at a reduced size to maintain its aspect ratio.
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===Event handlers===
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You can assign event handlers to any cell in liqbase and have a routine called when the event is required.
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New events can be dynamically created and utilized as required.
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====Linking handler to cell====
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<source lang="c">
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*vcell_handleradd(self,    "paint",  world_paint);
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</source>
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====Handler Code====
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<source lang="c">
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static int world_paint(vcell *self, vcellpainteventargs *args)
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{
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//liqapp_log("painting...");
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// tell the subsystem this event has been handled (returning 0 will cause the chain to continue)
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return 1;
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}
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</source>
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====Using a handler====
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<source lang="c">
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vcell_handlerrun(self,"paint",&paintargs);
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</source>
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[[Category:Software]]
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[[Category:Documentation]]
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