vo_opengl: separate kernel and window

This makes the core much more elegant, reusable, reconfigurable and also
allows us to more easily add aliases for specific configurations.

Furthermore, this lets us apply a generic blur factor / window function
to arbitrary filters, so we can finally "mix and match" in order to
fine-tune windowing functions.

A few notes are in order:

1. The current system for configuring scalers is ugly and rapidly
   getting unwieldy. I modified the man page to make it a bit more
   bearable, but long-term we have to do something about it; especially
   since..

2. There's currently no way to affect the blur factor or parameters of
   the window functions themselves. For example, I can't actually
   fine-tune the kaiser window's param1, since there's simply no way to
   do so in the current API - even though filter_kernels.c supports it
   just fine!

3. This removes some lesser used filters (especially those which are
   purely window functions to begin with). If anybody asks, you can get
   eg. the old behavior of scale=hanning by using
   scale=box:scale-window=hanning:scale-radius=1 (and yes, the result is
   just as terrible as that sounds - which is why nobody should have
   been using them in the first place).

4. This changes the semantics of the "triangle" scaler slightly - it now
   has an arbitrary radius. This can possibly produce weird results for
   people who were previously using scale-down=triangle, especially if
   in combination with scale-radius (for the usual upscaling). The
   correct fix for this is to use scale-down=bilinear_slow instead,
   which is an alias for triangle at radius 1.

In regards to the last point, in future I want to make it so that
filters have a filter-specific "preferred radius" (for the ones that
are arbitrarily tunable), once the configuration system for filters has
been redesigned (in particular in a way that will let us separate scale
and scale-down cleanly). That way, "triangle" can simply have the
preferred radius of 1 by default, while still being tunable. (Rather
than the default radius being hard-coded to 3 always)

1 files changed, 2 insertions, 0 deletions

diff --git a/video/out/gl_video.h b/video/out/gl_video.h
index 2f1203c40c..f3267d69c4 100644
--- a/video/out/gl_video.h
+++ b/video/out/gl_video.h
@@ -36,8 +36,10 @@ struct gl_video_opts {
     int target_prim;
     int target_trc;
     float scaler_params[3][2];
+    float scaler_blur[3];
     float scaler_radius[3];
     float scaler_antiring[3];
+    char *scaler_window[3];
     int linear_scaling;
     int fancy_downscaling;
     int sigmoid_upscaling;