[vlc-devel] [PATCH v2 21/22] opengl: document filters implementation

[Alexandre Janniaux]

Hi,

On Thu, Jul 02, 2020 at 06:03:20PM +0200, Romain Vimont wrote:
> On Thu, Jul 02, 2020 at 05:12:03PM +0200, Alexandre Janniaux wrote:
> > I feel that we also didn't choose about how to handle --gl-filter
> > addition/removal which would change the documentation here.
> >
> > What do you suggest currently?
>
> I agree with your suggestion here:
>
> https://mailman.videolan.org/pipermail/vlc-devel/2020-June/134926.html
>

Another solution would be to remove --gl-filter altogether
and merge the mock filter right after the opengl filter_t
patch, since we only need the renderer to work for now?

> > I'd suggest that we keep it until the opengl filter_t implementation
> > is merged though, so as to be able to test and review the patches
> > correctly.
>
> Once we can run them in the existing filtering system (filter_t), we
> could consider removing it. However, in my opinion, keeping it doesn't
> hurt, and it could help to investigate filter issues (like: when the
> result of a filter is black, does it work when executed in the vout?)
>
> >
> > Regards,
> > --
> > Alexandre Janniaux
> > Videolabs
> >
> > On Wed, Jul 01, 2020 at 12:30:22PM +0200, Romain Vimont wrote:
> > > Add an overview of the implementation of OpenGL filters.
> > >
> > > Co-authored-by: Alexandre Janniaux <ajanni at videolabs.io>
> > > ---
> > >  modules/video_output/opengl/filters.c | 78 +++++++++++++++++++++++++++
> > >  1 file changed, 78 insertions(+)
> > >
> > > diff --git a/modules/video_output/opengl/filters.c b/modules/video_output/opengl/filters.c
> > > index 66084b81cb..aefb8bff15 100644
> > > --- a/modules/video_output/opengl/filters.c
> > > +++ b/modules/video_output/opengl/filters.c
> > > @@ -32,6 +32,84 @@
> > >  #include "renderer.h"
> > >  #include "sampler_priv.h"
> > >
> > > +/* The filter chain contains the sequential list of filters, typically given
> > > + * via command-line arguments "--gl-filters=filter1:filter2:...:filtern".
> > > + *
> > > + * There are two types of filters:
> > > + *  - blend filters just draw over the provided framebuffer (containing the
> > > + *    result of the previous filter), without reading the input picture.
> > > + *  - non-blend filters read their input picture and draw whatever they want to
> > > + *    their own output framebuffer.
> > > + *
> > > + * For convenience, the filter chain does not store the filters as a single
> > > + * sequential list, but as a list of non-blend filters, each containing the
> > > + * list of their associated blend filters.
> > > + *
> > > + * For example, given:
> > > + *
> > > + *    --gl-filters=draw:triangle:triangle_mask:triangle_clock:triangle:renderer
> > > + *
> > > + * the filters chain stores the filters as follow:
> > > + *
> > > + *     +- draw               (non-blend)
> > > + *     |  +- triangle        (blend)
> > > + *     +- triangle_mask      (non-blend)
> > > + *     |  +- triangle_clock  (blend)
> > > + *     |  +- triangle        (blend)
> > > + *     +- renderer           (non-blend)
> > > + *
> > > + * An output framebuffer is created for each non-blend filters. It is used as
> > > + * draw framebuffer for that filter and all its associated blend filters.
> > > + *
> > > + * If the first filter is a blend filter, then a "draw" filter is automatically
> > > + * inserted. If the renderer does not appear in the filter list, it is
> > > + * automatically added at the end.
> > > + *
> > > + *
> > > + * ## Multisample anti-aliasing (MSAA)
> > > + *
> > > + * Each filter may also request multisample anti-aliasing, by providing a MSAA
> > > + * level during its Open(), for example:
> > > + *
> > > + *     filter->config.msaa_level = 4;
> > > + *
> > > + * For example:
> > > + *
> > > + *     +- draw               msaa_level=0
> > > + *     |  +- triangle        msaa_level=4
> > > + *     |  +- triangle_clock  msaa_level=2
> > > + *     +- renderer           msaa_level=0
> > > + *
> > > + * Among a "group" of one non-blend filter and its associated blend filters,
> > > + * the highest MSAA level (or 0 if multisampling is not supported) is assigned
> > > + * both to the non-blend filter, to configure its MSAA framebuffer, and to the
> > > + * blend filters, just for information and consistency:
> > > + *
> > > + *     +- draw               msaa_level=4
> > > + *     |  +- triangle        msaa_level=4
> > > + *     |  +- triangle_clock  msaa_level=4
> > > + *     +- renderer           msaa_level=0
> > > + *
> > > + * Some platforms (Android) do not support resolving multisample to the default
> > > + * framebuffer. Therefore, the msaa_level must always be 0 on the last filter.
> > > + * If this is not the case, a "draw" filter is automatically appended.
> > > + *
> > > + * For example:
> > > + *
> > > + *     +- draw               msaa_level=0
> > > + *     |  +- triangle        msaa_level=4
> > > + *     +- renderer           msaa_level=0
> > > + *        +- triangle_clock  msaa_level=2
> > > + *
> > > + * will become:
> > > + *
> > > + *     +- draw               msaa_level=4
> > > + *     |  +- triangle        msaa_level=4
> > > + *     +- renderer           msaa_level=2
> > > + *     |  +- triangle_clock  msaa_level=2
> > > + *     +- draw               msaa_level=0
> > > + */
> > > +
> > >  struct vlc_gl_filters {
> > >      struct vlc_gl_t *gl;
> > >      const struct vlc_gl_api *api;
> > > --
> > > 2.27.0
> > >
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