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Original commit message from CVS: 2004-01-28 Ronald Bultje <rbultje@ronald.bitfreak.net> * docs/pwg/advanced_clock.xml: * docs/pwg/advanced_interfaces.xml: * docs/pwg/advanced_midi.xml: General placeholders for now. * docs/pwg/advanced_request.xml: Explanation about sometimes and request pads. * docs/pwg/advanced_scheduling.xml: Concept of bytestream, loopfunctions and schedulers. * docs/pwg/building_boiler.xml: Add something about plugin-init.
105 lines
3.8 KiB
XML
105 lines
3.8 KiB
XML
<chapter id="cha-advanced-interfaces">
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<title>Interfaces</title>
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<para>
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Previously, in the chapter <xref linkend="cha-building-args"/>, we have
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introduced the concept of GObject properties of controlling an element's
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behaviour. This is a very powerful, but has two big disadvantage: firstly,
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it is too generic, and secondly, it isn't dynamic.
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</para>
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<para>
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The first disadvantage has to do with customizability of the end-user
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interface that will be built to control the element. Some properties are
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more important than others. Some integer properties are better shown in a
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spin-button widget, whereas others would be better represented by a slider
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widget. Such things are not possible because the UI has no actual meaning
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in the application. A UI widget that stands for a bitrate property is the
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same as an UI widget that stands for the size of a video, as long as both
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are of the same <classname>GParamSpec</classname> type. Another problem,
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related to the one about parameter important, is that things like parameter
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grouping, function grouping or anything to make parameters coherent, is not
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really possible.
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</para>
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<para>
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The second argument against parameters are that they are not dynamic. In
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many cases, the allowed values for a property are not fixed, but depend
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on things that can only be detected at run-time. The names of inputs for
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a TV card in a video4linux source element, for example, can only be
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retrieved from the kernel driver when we've opened the device; this only
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happens when the element goes into the READY state. This means that we
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cannot create an enum property type to show this to the user.
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</para>
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<para>
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The solution to those problems is to create very specialized types of
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controls for certain often-used controls. We use the concept of interfaces
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to achieve this. The basis of this all is the glib
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<classname>GTypeInterface</classname> type. For each case where we think
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it's useful, we've created interfaces which can be implemented by elements
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at their own will. We've also created a small extension to
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<classname>GTypeInterface</classname> (which is static itself, too) which
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allows us to query for interface availability based on runtime properties.
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This extension is called <classname>GstImplementsInterface</classname>.
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</para>
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<sect1 id="sect1-iface-general" xreflabel="How to Implement Interfaces">
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<title>How to Implement Interfaces</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-mixer" xreflabel="Mixer Interface">
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<title>Mixer Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-tuner" xreflabel="Tuner Interface">
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<title>Tuner Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-colorbalance" xreflabel="Color Balance Interface">
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<title>Color Balance Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-propprobe" xreflabel="Property Probe Interface">
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<title>Property Probe Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-profile" xreflabel="Profile Interface">
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<title>Profile Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-xoverlay" xreflabel="X Overlay Interface">
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<title>X Overlay Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-navigation" xreflabel="Navigation Interface">
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<title>Navigation Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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<sect1 id="sect1-iface-tagging" xreflabel="Tagging Interface">
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<title>Tagging Interface</title>
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<para>
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WRITEME
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</para>
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</sect1>
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</chapter>
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