Extending The Effects Engine Report W10

Hello,

The LV2EffectProcessor class is now implemented. It dynamically creates an EngineEffectParameter* for each effect parameter it extracts from the EffectManifest. It has 4 float arrays which are I/O buffers (input left, input right, output left, output right). Also it features a params array which is used to communicate parameter changes to the plugin instance. This class' constructor receives a const LilvPlugin* which is passed as a parameter to lilv_plugin_instantiate function. This is the first function which needs to be called. The next step is using lilv_instance_connect_port to connect the plugin's ports to chunks of memory. For example, audio ports need to be connected to float arrays, while each control port communicates through a single float value. To be able to differentiate between those two types of ports I use two lists of indices: one which stores the audio port indices and another one which stores the control port indices. lilv_instance_activate is the next function we need to call. It resets all state information in the plugin, except for previously assigned port data locations. Inside LV2EffectProcessor::process we update the parameter array with values extracted from each EngineEffectParameter. Now all we have to do is split the input into channels (L and R), call lilv_instance_run and combine the resulting samples into an interleaved stereo output. The plugin instance is deactivated and freed inside the destructor.

LV2 plugins can have enumeration ports as parameters which can be represented as drop down lists. However, it is an open debate about how this type of parameters should be introduced into Mixxx's Effects Framework. For the moment, I added a new ValueHint to EffectManifestParameter: VALUE_ENUMERATION. For each enumeration port, I extracted a list of pairs which contains the description and the value for each enumeration entry. I used lilv_port_get_scale_points to obtain the options, I iterated through them and used lilv_scale_point_get function to get the value and lilv_scale_point_get_label function to get the description of each scale point (enumeration entry).

Daniel had some issues with the lilv library, so I added a Lilv class to features.py. I hope this solves the problem with lilv library linking.

Also, I have added kill buttons to Butterworth8EQEffect and opened a pull request[1]. I am currently waiting for feedback. It depends if we want to go this way with button and enumeration parameters, or tackle this problem differently.

As a side task, I added search functionality to developer's log. I needed this feature while doing some debugging. I used Qt Creator to insert a QLineEdit and a QPushButton to the GUI. Inside dlgdevelopertools.cpp I connedted QLineEdit's returnPressed() and QPushButton's clicked() signals to a newly added slot, slotLogSearch(). Here[2] is the PR I opened for this feature. Tell me what you think about it. In my opinion, this might be handy for some developers.

Stay tuned for updates,
Nicu Badescu
[1] - https://github.com/mixxxdj/mixxx/pull/297
[2] - https://github.com/mixxxdj/mixxx/pull/300
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