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40 lines
1.8 KiB
Text
40 lines
1.8 KiB
Text
Controller
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----------
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The controller subsystem allows to automate element property changes. It works
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so that all parameter changes are time based and elements request property
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updates at processing time.
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Element view
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~~~~~~~~~~~~
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Elements don't need to do much. They need to:
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- mark object properties that can be changed while processing with
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GST_PARAM_CONTROLLABLE
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- call gst_object_sync_values (self, timestamp) in the processing function
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before accessing the parameters.
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All ordered property types can be automated (int, double, boolean, enum).
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Application view
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~~~~~~~~~~~~~~~~
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Applications need to setup the property automation. For that they need to create
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a GstControlSource and attach it to a property using GstControlBinding. Various
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control-sources and control-bindings exist. All control sources produce control
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value sequences in the form of gdouble values. The control bindings map them to
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the value range and type of the bound property.
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One control-source can be attached to one or more properties at the same time.
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If it is attached multiple times, then each control-binding will scale and
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convert the control values to the target property type and range.
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One can create complex control-curves by using a GstInterpolationControlSource.
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This allows the classic user editable control-curve (often seen in audio/video
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editors). Another way is to use computed control curves. GstLFOControlSource can
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generate various repetitive signals. Those can be made more complex by chaining
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the control sources. One can attach another control-source to e.g. modulate the
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frequency of the first GstLFOControlSource.
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In most cases GstControlBindingDirect will be the binding to be used. Other
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control bindings are there to handle special cases, such as having 1-4 control-
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sources and combine their values into a single guint to control a rgba-color
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property.
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