vo_opengl: use textureGatherOffset for polar filters

This is more efficient on my machine (nvidia), but only when applied to
groups of exactly 4 texels. So we switch to the more efficient
textureGather for groups of 4. Some notes:

- textureGatherOffset seems to be faster than textureGather by a
  non-negligible amount, but for some reason, textureOffset is still
  slower than a straight-up texture
- textureGather* requires GLSL 400; and at least on nvidia, this
  requires actually allocating a GL 4.0 context.
- the code in opengl/common.c that clamped the GLSL version to 330 is
  deprecated, because the old user shader style has been removed
  completely in the meantime
- To combat the growing complexity of the polar sampling code, we drop
  the antiringing functionality from EWA shaders completely, since it
  never really worked well for EWA to begin with. (Horrific artifacting)

1 files changed, 2 insertions, 1 deletions

diff --git a/video/out/opengl/video_shaders.h b/video/out/opengl/video_shaders.h
index 207824b169..6498033ad1 100644
--- a/video/out/opengl/video_shaders.h
+++ b/video/out/opengl/video_shaders.h
@@ -30,7 +30,8 @@ extern const struct m_sub_options deband_conf;
 void sampler_prelude(struct gl_shader_cache *sc, int tex_num);
 void pass_sample_separated_gen(struct gl_shader_cache *sc, struct scaler *scaler,
                                int d_x, int d_y);
-void pass_sample_polar(struct gl_shader_cache *sc, struct scaler *scaler);
+void pass_sample_polar(struct gl_shader_cache *sc, struct scaler *scaler,
+                       int components, int glsl_version);
 void pass_sample_bicubic_fast(struct gl_shader_cache *sc);
 void pass_sample_oversample(struct gl_shader_cache *sc, struct scaler *scaler,
                             int w, int h);