vo_opengl: also expose NAME_mul for user shaders

This is exposed so that bjin/mpv-prescalers can use textureGatherOffset
for performance.

Since there are now quite a lot of parameters where it isn't quite clear
why they're all defined, add a paragraph to the man page that explains
them a bit.

1 files changed, 8 insertions, 0 deletions

diff --git a/DOCS/man/options.rst b/DOCS/man/options.rst
index 7e6199b5e3..2e48c51ffa 100644
--- a/DOCS/man/options.rst
+++ b/DOCS/man/options.rst
@@ -4274,10 +4274,18 @@ The following video options are currently all specific to ``--vo=opengl`` and
         to texture coordinates)
     vec2 NAME_pt
         The (unrotated) size of a single pixel, range [0,1].
+    float NAME_mul
+        The coefficient that needs to be multiplied into the texture contents
+        in order to normalize it to the range [0,1].
     sampler NAME_raw
         The raw bound texture itself. The use of this should be avoided unless
         absolutely necessary.
 
+    Normally, users should use either NAME_tex or NAME_texOff to read from the
+    texture. For some shaders however , it can be better for performance to do
+    custom sampling from NAME_raw, in which case care needs to be taken to
+    respect NAME_mul and NAME_rot.
+
     In addition to these parameters, the following uniforms are also globally
     available: