Extending The Effects Engine Report W12

Hello,

As you know from the last report, button and enumeration parameters were using a multi state button for cycling through its states. The downside of this was that the user had no visual feedback of which option is he going to choose. Also, he couldn't skip skip through the states, they were incremented by one each time the button was pressed.

I managed to solve this issue by creating another widget, called WEffectPushButton which is borrowing code for acting like a push button from WPushButton widget and code for obtaining information about the loaded effect from the WEffectParameter. A new tag for buttons used inside the effects framework was introduced, EffectPushButton. It shall be used by skin developers when they create a new skin. Inside legacyskinparser.cpp a new method for parsing the newly added tag was introduced: parseEffectPushButton.

It is responsible for setting up the required connection, as well as creating a new WEffectPushButton object. This new widget acts the same when the user left clicks it: cycles through the states. But it has a different behaviour on right click: opens a small menu with all options available for that parameter. QMenu was used for this, along with a QActionGroup which acts like a container for QAction entries, allowing us to make the QAction exclusive (only one can be checked at a given time). Here is an image of the output, using a modified Deere skin:

Another issue with LV2 effects was that some of them had a lot of parameters (up to 60) and they can't possibly fit inside a skin. So the solution I came up with was letting the user select which parameters are displayed inside the skin. This is done via an LV2 preferences menu which displays all the discovered LV2 plugins as buttons. Those which are not available are shown as disabled push buttons. Upon clicking an effect, its parameters are displayed as check boxes and the user can set the active parameters.

This was achieved by introducing a list inside EffectManifest which acts like a function which job is to map a parameter slot to the index of the effect's active parameter for that slot. For example, if we want effect's parameters 4, 7 and 10 to be active, the mapping function would be: f[0] = 4, f[1] = 7 and f[2] = 10. This function was built on demand, whenever a new EffectManifestParameter was added to an EffectManifest.

While working on this, I got an "index out of bounds" and it took me quite a while to figure out what was the problem. Inside EffectParamterSlot::loadEffect method it was possible to ask for a parameter which did not exist. It was the caller's responsibility to ensure the parameter was returned and not NULL. Well, in this case, the mapping function did not have any value for the requested parameter slot number, because it was greater than the number of real parameters. So I replaced Effect::getParameter and Effect::getButtonParameter methods with Effect::getParameterForSlot and Effect::getButtonParamterForSlot. These new methods perform an upper bound check and retrieve the proper EffectParameter by using the mapping function provided by the EffectManifest. Here is how the LV2 preferences menu currently looks:

I also worked on the Graphic EQ effect. Daniel added a pauseFilter() method which I had to use when a filter was paused or restarted. This resets the buffers and sets m_doRamping and m_doStart flags to true. In order to avoid resetting the buffers each time the process method is called and the filter is paused, I had to introduce a new flag, m_isPaused. Here[1] you can check the commit which introduces that flag. Another addition to Graphic EQ effect is the dynamic updated of the filters if the sample rate is changed. It cycles through the band filters and calls setFrequencyCorners on each one with the new value of sample rate.

Today is the suggested pencils down date. I am happy with my progress and I will spend the last week of GSoC removing debug comments across the code I wrote and trying to create a better GUI for the LV2 preferences.

Cheers,
Nicu Badescu

[1] - https://github.com/badescunicu/mixxx/commit/8ce1b54885d637ad9a35ce82d9eded9ccb885ffd

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