vo_gpu: add --tone-mapping-mode

This merges the old desaturation control options into a single
enumeration, with the goal of both simplifying how these options work
and also making this list more extensible (including, notably, new
options only supported by vo_gpu_next).

For the hybrid option, I decided to port the (slightly tweaked) values
from libplacebo's pre-refactor defaults, rather than the old values we
had in mpv, to more visually match the look of the vo_gpu_next hybrid.

6 files changed, 80 insertions, 40 deletions

diff --git a/DOCS/interface-changes.rst b/DOCS/interface-changes.rst
index 75516627df..48c5b62881 100644
--- a/DOCS/interface-changes.rst
+++ b/DOCS/interface-changes.rst
@@ -36,6 +36,8 @@ Interface changes
     - add `--tone-mapping` options `auto`, `spline` and `bt.2446a`
     - add `--inverse-tone-mapping`
     - add `--gamut-mapping-mode`, replacing `--gamut-clipping` and `--gamut-warning`
+    - add `--tone-mapping-mode`, replacing `--tone-mapping-desaturate` and
+      `--tone-mapping-desaturate-exponent`.
  --- mpv 0.34.0 ---
     - deprecate selecting by card number with `--drm-connector`, add
       `--drm-device` which can be used instead
diff --git a/DOCS/man/options.rst b/DOCS/man/options.rst
index bd2b9be470..7b51b585e8 100644
--- a/DOCS/man/options.rst
+++ b/DOCS/man/options.rst
@@ -6385,6 +6385,28 @@ them.
     it too high will make dark scenes appear unnaturally bright. (``-vo=gpu``
     only)
 
+``--tone-mapping-mode``
+    Controls how the tone mapping function is applied to colors.
+
+    auto
+        Choose the best mode automatically. (Default)
+    rgb
+        Tone-map per-channel (RGB). Has a tendency to severely distort colors,
+        desaturate highlights, and is generally not very recommended. However,
+        this is the mode used in many displays and TVs (especially early ones),
+        and so sometimes it's needed to reproduce the artistic intent a film
+        was mastered with.
+    max
+        Tone-map on the brightest component in the video. Has a tendency to
+        lead to weirdly oversaturated colors, and loss of dark details.
+    hybrid
+        A hybrid approach that uses linear tone-mapping for midtones and
+        per-channel tone mapping for highlights.
+    luma
+        Luminance-based method from ITU-R BT.2446a, including fixed gamut
+        reductions to account for brightness-related perceptual nonuniformity.
+        (``--vo=gpu-next`` only)
+
 ``--gamut-mapping-mode``
     Specifies the algorithm used for reducing the gamut of images for the
     target display, after any tone mapping is done.
@@ -6445,27 +6467,6 @@ them.
     aggressive, up to the limit of the high threshold (at which point the
     filter becomes instant).
 
-``--tone-mapping-desaturate=<0.0..1.0>``
-    Apply desaturation for highlights (default: 0.75). The parameter controls
-    the strength of the desaturation curve. A value of 0.0 completely disables
-    it, while a value of 1.0 means that overly bright colors will tend towards
-    white. This is not always the case, especially not for highlights that are
-    near primary colors. (``--vo=gpu`` only)
-
-    Values in between apply progressively more/less aggressive desaturation.
-    This setting helps prevent unnaturally oversaturated colors for
-    super-highlights, by (smoothly) turning them into less saturated (per
-    channel tone mapped) colors instead. This makes images feel more natural,
-    at the cost of chromatic distortions for out-of-range colors. The default
-    value of 0.75 provides a good balance. Setting this to 0.0 preserves the
-    chromatic accuracy of the tone mapping process.
-
-``--tone-mapping-desaturate-exponent=<0.0..20.0>``
-    This setting controls the exponent of the desaturation curve, which
-    controls how bright a color needs to be in order to start being
-    desaturated. The default of 1.5 provides a reasonable balance.  Decreasing
-    this exponent makes the curve more aggressive.
-
 ``--use-embedded-icc-profile``
     Load the embedded ICC profile contained in media files such as PNG images.
     (Default: yes). Note that this option only works when also using a display
diff --git a/video/out/gpu/video.c b/video/out/gpu/video.c
index 8236a7b43f..d0d0509792 100644
--- a/video/out/gpu/video.c
+++ b/video/out/gpu/video.c
@@ -329,8 +329,6 @@ static const struct gl_video_opts gl_video_opts_def = {
         .decay_rate = 100.0,
         .scene_threshold_low = 5.5,
         .scene_threshold_high = 10.0,
-        .desat = 0.75,
-        .desat_exp = 1.5,
     },
     .early_flush = -1,
     .hwdec_interop = "auto",
@@ -394,9 +392,12 @@ const struct m_sub_options gl_video_conf = {
             M_RANGE(0.0, 0.3)},
         {"tone-mapping-max-boost", OPT_FLOAT(tone_map.max_boost),
             M_RANGE(1.0, 10.0)},
-        {"tone-mapping-desaturate", OPT_FLOAT(tone_map.desat)},
-        {"tone-mapping-desaturate-exponent", OPT_FLOAT(tone_map.desat_exp),
-            M_RANGE(0.0, 20.0)},
+        {"tone-mapping-mode", OPT_CHOICE(tone_map.mode,
+            {"auto",        TONE_MAP_MODE_AUTO},
+            {"rgb",         TONE_MAP_MODE_RGB},
+            {"max",         TONE_MAP_MODE_MAX},
+            {"hybrid",      TONE_MAP_MODE_HYBRID},
+            {"luma",        TONE_MAP_MODE_LUMA})},
         {"gamut-mapping-mode", OPT_CHOICE(tone_map.gamut_mode,
             {"auto",        GAMUT_AUTO},
             {"clip",        GAMUT_CLIP},
@@ -479,6 +480,8 @@ const struct m_sub_options gl_video_conf = {
                                         "--linear-downscaling")},
         {"gamut-warning", OPT_REMOVED("Replaced by --gamut-mapping-mode=warn")},
         {"gamut-clipping", OPT_REMOVED("Replaced by --gamut-mapping-mode=desaturate")},
+        {"tone-mapping-desaturate", OPT_REMOVED("Replaced by --tone-mapping-mode")},
+        {"tone-mapping-desaturate-exponent", OPT_REMOVED("Replaced by --tone-mapping-mode")},
         {0}
     },
     .size = sizeof(struct gl_video_opts),
@@ -2644,6 +2647,18 @@ static void pass_colormanage(struct gl_video *p, struct mp_colorspace src,
         break;
     }
 
+    switch (p->opts.tone_map.mode) {
+    case TONE_MAP_MODE_AUTO:
+    case TONE_MAP_MODE_RGB:
+    case TONE_MAP_MODE_MAX:
+    case TONE_MAP_MODE_HYBRID:
+        break;
+    default:
+        MP_WARN(p, "Tone mapping mode unsupported by vo_gpu, falling back.\n");
+        p->opts.tone_map.mode = TONE_MAP_MODE_AUTO;
+        break;
+    }
+
     switch (p->opts.tone_map.gamut_mode) {
     case GAMUT_AUTO:
     case GAMUT_WARN:
diff --git a/video/out/gpu/video.h b/video/out/gpu/video.h
index adeadaba65..0bb180e514 100644
--- a/video/out/gpu/video.h
+++ b/video/out/gpu/video.h
@@ -100,6 +100,14 @@ enum tone_mapping {
     TONE_MAPPING_BT_2446A,
 };
 
+enum tone_mapping_mode {
+    TONE_MAP_MODE_AUTO,
+    TONE_MAP_MODE_RGB,
+    TONE_MAP_MODE_MAX,
+    TONE_MAP_MODE_HYBRID,
+    TONE_MAP_MODE_LUMA,
+};
+
 enum gamut_mode {
     GAMUT_AUTO,
     GAMUT_CLIP,
@@ -114,12 +122,11 @@ struct gl_tone_map_opts {
     float max_boost;
     int inverse;
     float crosstalk;
+    int mode;
     int compute_peak;
     float decay_rate;
     float scene_threshold_low;
     float scene_threshold_high;
-    float desat;
-    float desat_exp;
     int gamut_mode;
 };
 
diff --git a/video/out/gpu/video_shaders.c b/video/out/gpu/video_shaders.c
index 6dcef77fa0..9628274b19 100644
--- a/video/out/gpu/video_shaders.c
+++ b/video/out/gpu/video_shaders.c
@@ -809,18 +809,24 @@ static void pass_tone_map(struct gl_shader_cache *sc,
         abort();
     }
 
-    GLSL(vec3 sig_lin = color.rgb * (sig[sig_idx] / sig_orig);)
-
-    // Mix between the per-channel tone mapped and the linear tone mapped
-    // signal based on the desaturation strength
-    if (opts->desat > 0) {
-        float base = 0.18 * dst_scale;
-        GLSLF("float coeff = max(sig[sig_idx] - %f, 1e-6) / "
-              "              max(sig[sig_idx], 1.0);\n", base);
-        GLSLF("coeff = %f * pow(coeff, %f);\n", opts->desat, opts->desat_exp);
-        GLSLF("color.rgb = mix(sig_lin, %f * sig, coeff);\n", dst_scale);
-    } else {
-        GLSL(color.rgb = sig_lin;)
+    switch (opts->mode) {
+    case TONE_MAP_MODE_RGB:
+        GLSL(color.rgb = sig;)
+        break;
+    case TONE_MAP_MODE_MAX:
+        GLSL(color.rgb *= sig[sig_idx] / sig_orig;)
+        break;
+    case TONE_MAP_MODE_AUTO:
+    case TONE_MAP_MODE_HYBRID:
+        GLSLF("float coeff = max(sig[sig_idx] - %f, 1e-6) / \n"
+              "              max(sig[sig_idx], 1.0);        \n"
+              "coeff = %f * pow(coeff / %f, %f);            \n"
+              "color.rgb *= sig[sig_idx] / sig_orig;        \n"
+              "color.rgb = mix(color.rgb, %f * sig, coeff); \n",
+              0.18 / dst_scale, 0.90, dst_scale, 0.20, dst_scale);
+        break;
+    default:
+        abort();
     }
 }
 
diff --git a/video/out/vo_gpu_next.c b/video/out/vo_gpu_next.c
index 390852ff71..9bbb58101f 100644
--- a/video/out/vo_gpu_next.c
+++ b/video/out/vo_gpu_next.c
@@ -1406,12 +1406,21 @@ static void update_render_options(struct priv *p)
         [GAMUT_DARKEN]          = PL_GAMUT_DARKEN,
     };
 
+    static const enum pl_tone_map_mode tone_map_modes[] = {
+        [TONE_MAP_MODE_AUTO]    = PL_TONE_MAP_AUTO,
+        [TONE_MAP_MODE_RGB]     = PL_TONE_MAP_RGB,
+        [TONE_MAP_MODE_MAX]     = PL_TONE_MAP_MAX,
+        [TONE_MAP_MODE_HYBRID]  = PL_TONE_MAP_HYBRID,
+        [TONE_MAP_MODE_LUMA]    = PL_TONE_MAP_LUMA,
+    };
+
     p->color_map = pl_color_map_default_params;
     p->color_map.intent = opts->icc_opts->intent;
     p->color_map.tone_mapping_function = tone_map_funs[opts->tone_map.curve];
     p->color_map.tone_mapping_param = opts->tone_map.curve_param;
     p->color_map.inverse_tone_mapping = opts->tone_map.inverse;
     p->color_map.tone_mapping_crosstalk = opts->tone_map.crosstalk;
+    p->color_map.tone_mapping_mode = tone_map_modes[opts->tone_map.mode];
     if (isnan(p->color_map.tone_mapping_param)) // vo_gpu compatibility
         p->color_map.tone_mapping_param = 0.0;
     if (opts->tone_map.gamut_mode != GAMUT_AUTO)