vo_gpu: vo_gpu_next: support --icc-3dlut-size=auto

And make it the default. In libplacebo, this uses internal heuristics to
pick a good size based on the actual ICC characteristics. This is
significantly less wasteful than always generating a 64x64x64 3DLUT (the
old status quo).

In vo_gpu, for simplicity, just default to 65x65x65. Note that this
provides slightly better accuracy than the old default of 64x64x64 for
technical reasons, and matches what libplacebo defaults to for typical
display profiles.

DOCS/interface-changes.rst

@@ -57,6 +57,7 @@ Interface changes
     - add `video-params/crop-[w,h,x,y]`
     - remove `--tone-mapping-mode`
     - change `--subs-fallback-forced` so that it works alongside `--slang`
+    - add `--icc-3dlut-size=auto` and make it the default
  --- mpv 0.36.0 ---
     - add `--target-contrast`
     - Target luminance value is now also applied when ICC profile is used.

DOCS/man/options.rst

@@ -6812,9 +6812,10 @@ them.
     3
         absolute colorimetric
 
-``--icc-3dlut-size=<r>x<g>x<b>``
-    Size of the 3D LUT generated from the ICC profile in each dimension.
-    Default is 64x64x64. Sizes may range from 2 to 512.
+``--icc-3dlut-size=<auto|RxGxB>``
+    Size of the 3D LUT generated from the ICC profile in each dimension. The
+    default of ``auto`` means to pick the size automatically based on internal
+    heuristics. Sizes may range from 2 to 512.
 
 ``--icc-force-contrast=<no|0-1000000|inf>``
     Override the target device's detected contrast ratio by a specific value.

video/out/gpu/lcms.c

@@ -326,6 +326,12 @@ bool gl_lcms_get_lut3d(struct gl_lcms *p, struct lut3d **result_lut3d,
     if (!gl_lcms_has_profile(p))
         return false;
 
+    // For simplicity, default to 65x65x65, which is large enough to cover
+    // typical profiles with good accuracy while not being too wasteful
+    s_r = s_r ? s_r : 65;
+    s_g = s_g ? s_g : 65;
+    s_b = s_b ? s_b : 65;
+
     void *tmp = talloc_new(NULL);
     uint16_t *output = talloc_array(tmp, uint16_t, s_r * s_g * s_b * 4);
     struct lut3d *lut = NULL;
@@ -514,7 +520,7 @@ const struct m_sub_options mp_icc_conf = {
     },
     .size = sizeof(struct mp_icc_opts),
     .defaults = &(const struct mp_icc_opts) {
-        .size_str = "64x64x64",
+        .size_str = "auto",
         .intent = MP_INTENT_RELATIVE_COLORIMETRIC,
         .use_embedded = true,
         .cache = true,

video/out/gpu/lcms.h

@@ -44,6 +44,10 @@ bool gl_lcms_has_changed(struct gl_lcms *p, enum mp_csp_prim prim,
 
 static inline bool gl_parse_3dlut_size(const char *arg, int *p1, int *p2, int *p3)
 {
+    if (!strcmp(arg, "auto")) {
+        *p1 = *p2 = *p3 = 0;
+        return true;
+    }
     if (sscanf(arg, "%dx%dx%d", p1, p2, p3) != 3)
         return false;
     for (int n = 0; n < 3; n++) {