vo_gpu: add better gamut clipping option

See https://code.videolan.org/videolan/libplacebo/-/commit/d63eeb1ecc204 Enabled by default because I think it looks better. YMMV.
mpv-player · Jun 19, 2020 · dc24a43 · dc24a43 · Doofussy2 · Jun 23, 2020
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diff --git a/DOCS/man/options.rst b/DOCS/man/options.rst
@@ -6167,6 +6167,13 @@ The following video options are currently all specific to ``--vo=gpu`` and
     well with ICC profiles, since the 3DLUTs are always generated against the
     source color space and have chromatically-accurate clipping built in.
 
+``--gamut-clipping``
+    If enabled (default: yes), mpv will colorimetrically clip out-of-gamut
+    colors by desaturating them (preserving luma), rather than hard-clipping
+    each component individually. This should make playback of wide gamut
+    content on typical (standard gamut) monitors look much more aesthetically
+    pleasing and less blown-out.
+
 ``--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
@@ -330,6 +330,7 @@ static const struct gl_video_opts gl_video_opts_def = {
         .scene_threshold_high = 10.0,
         .desat = 0.75,
         .desat_exp = 1.5,
+        .gamut_clipping = 1,
     },
     .early_flush = -1,
     .hwdec_interop = "auto",
@@ -401,6 +402,7 @@ const struct m_sub_options gl_video_conf = {
         {"tone-mapping-desaturate-exponent", OPT_FLOAT(tone_map.desat_exp),
             M_RANGE(0.0, 20.0)},
         {"gamut-warning", OPT_FLAG(tone_map.gamut_warning)},
+        {"gamut-clipping", OPT_FLAG(tone_map.gamut_clipping)},
         {"opengl-pbo", OPT_FLAG(pbo)},
         SCALER_OPTS("scale",  SCALER_SCALE),
         SCALER_OPTS("dscale", SCALER_DSCALE),

diff --git a/video/out/gpu/video.h b/video/out/gpu/video.h
@@ -108,6 +108,7 @@ struct gl_tone_map_opts {
     float desat;
     float desat_exp;
     int gamut_warning; // bool
+    int gamut_clipping; // bool
 };
 
 struct gl_video_opts {

diff --git a/video/out/gpu/video_shaders.c b/video/out/gpu/video_shaders.c
@@ -870,6 +870,17 @@ void pass_color_map(struct gl_shader_cache *sc, bool is_linear,
         mp_get_cms_matrix(csp_src, csp_dst, MP_INTENT_RELATIVE_COLORIMETRIC, m);
         gl_sc_uniform_mat3(sc, "cms_matrix", true, &m[0][0]);
         GLSL(color.rgb = cms_matrix * color.rgb;)
+
+        if (opts->gamut_clipping) {
+            GLSL(float cmin = min(min(color.r, color.g), color.b);)
+            GLSL(if (cmin < 0.0) {
+                     float luma = dot(dst_luma, color.rgb);
+                     float coeff = cmin / (cmin - luma);
+                     color.rgb = mix(color.rgb, vec3(luma), coeff);
+                 })
+            GLSL(float cmax = max(max(color.r, color.g), color.b);)
+            GLSL(if (cmax > 1.0) color.rgb /= cmax;)
+        }
     }
 
     if (need_ootf)