vo_opengl: make the default debanding settings less excessive

It's great that the new algorithm supports multiple placebo iterations
and all, but it's really not necessary and hurts performance in the
general case for the sake of the 0.1% that actually pause the screen
and look for minute differences.

Signed-off-by: wm4 <wm4@nowhere>

DOCS/man/vo.rst

@@ -611,11 +611,8 @@ Available video output drivers are:
     ``deband-iterations=<1..16>``
         The number of debanding steps to perform per sample. Each step reduces
         a bit more banding, but takes time to compute. Note that the strength
-        of each step falls off very quickly, so high numbers are practically
-        useless. (Default 4)
-
-        If the performance hit of debanding is too great, you can reduce this
-        to 2 or 1 with marginal visual quality loss.
+        of each step falls off very quickly, so high numbers (>4) are
+        practically useless. (Default 1)
 
     ``deband-threshold=<0..4096>``
         The debanding filter's cut-off threshold. Higher numbers increase the
@@ -625,7 +622,10 @@ Available video output drivers are:
     ``deband-range=<1..64>``
         The debanding filter's initial radius. The radius increases linearly
         for each iteration. A higher radius will find more gradients, but
-        a lower radius will smooth more aggressively. (Default 8)
+        a lower radius will smooth more aggressively. (Default 16)
+
+        If you increase the ``deband-iterations``, you should probably
+        decrease this to compensate.
 
     ``deband-grain=<0..4096>``
         Add some extra noise to the image. This significantly helps cover up

video/out/opengl/video_shaders.c

@@ -326,9 +326,9 @@ struct deband_opts {
 };
 
 const struct deband_opts deband_opts_def = {
-    .iterations = 4,
+    .iterations = 1,
     .threshold = 64.0,
-    .range = 8.0,
+    .range = 16.0,
     .grain = 48.0,
 };