vo_opengl: enable pbo by default with opengl-hq

Can significantly help with very large video resolutions on nvidia
drivers. It doesn't seem to have negative effects on Intel drivers
either. (Although it could have on Intel drivers for older hardware.)

For now, this is only for --vo=opengl-hq. Maybe --vo=opengl should use
it too, but it's still meant to be the crappy, fail-safe default.

DOCS/man/vo.rst

@@ -821,7 +821,7 @@ Available video output drivers are:
 
     This is equivalent to::
 
-        --vo=opengl:scale=spline36:cscale=spline36:dscale=mitchell:dither-depth=auto:fancy-downscaling:sigmoid-upscaling
+        --vo=opengl:scale=spline36:cscale=spline36:dscale=mitchell:dither-depth=auto:fancy-downscaling:sigmoid-upscaling:pbo
 
     Note that some cheaper LCDs do dithering that gravely interferes with
     ``opengl``'s dithering. Disabling dithering with ``dither-depth=no`` helps.

video/out/gl_video.c

@@ -365,6 +365,7 @@ const struct gl_video_opts gl_video_opts_hq_def = {
     .background = {0, 0, 0, 255},
     .gamma = 1.0f,
     .blend_subs = 0,
+    .pbo = 1,
 };
 
 static int validate_scaler_opt(struct mp_log *log, const m_option_t *opt,