vo_opengl: implement the Panasonic V-Log function

User request and not that hard. Closes #3157.

Note that FFmpeg doesn't support this and there's no signalling in HEVC
etc., so the only way users can access it is by using vf_format
manually.

Mind: This encoding uses full range values, not TV range.

DOCS/man/vf.rst

@@ -314,6 +314,7 @@ Available filters are:
        :prophoto:     ProPhoto RGB (ROMM) curve
        :st2084:       SMPTE ST2084 (HDR) curve
        :std-b67:      ARIB STD-B67 (Hybrid Log-gamma) curve
+       :v-log:        Panasonic V-Log transfer curve
 
     ``<peak>``
         Reference peak illumination for the video file. This is mostly

DOCS/man/vo.rst

@@ -1007,6 +1007,8 @@ Available video output drivers are:
             SMPTE ST2084 (HDR) curve, PQ OETF
         std-b67
             ARIB STD-B67 (Hybrid Log-gamma) curve, also known as BBC/NHK HDR
+        v-log
+            Panasonic V-Log (VARICAM) curve
 
         NOTE: When using HDR output formats, mpv will encode to the specified
               curve but it will not set any HDMI flags or other signalling that

video/csputils.c

@@ -80,6 +80,7 @@ const struct m_opt_choice_alternatives mp_csp_trc_names[] = {
     {"prophoto",    MP_CSP_TRC_PRO_PHOTO},
     {"st2084",      MP_CSP_TRC_SMPTE_ST2084},
     {"std-b67",     MP_CSP_TRC_ARIB_STD_B67},
+    {"v-log",       MP_CSP_TRC_V_LOG},
     {0}
 };
 

video/csputils.h

@@ -81,6 +81,7 @@ enum mp_csp_trc {
     MP_CSP_TRC_PRO_PHOTO,
     MP_CSP_TRC_SMPTE_ST2084,
     MP_CSP_TRC_ARIB_STD_B67,
+    MP_CSP_TRC_V_LOG,
     MP_CSP_TRC_COUNT
 };
 

video/mp_image.c

@@ -611,8 +611,13 @@ void mp_image_params_guess_csp(struct mp_image_params *params)
         }
         if (params->colorspace == MP_CSP_AUTO)
             params->colorspace = mp_csp_guess_colorspace(params->w, params->h);
-        if (params->colorlevels == MP_CSP_LEVELS_AUTO)
-            params->colorlevels = MP_CSP_LEVELS_TV;
+        if (params->colorlevels == MP_CSP_LEVELS_AUTO) {
+            if (params->gamma == MP_CSP_TRC_V_LOG) {
+                params->colorlevels = MP_CSP_LEVELS_PC;
+            } else {
+                params->colorlevels = MP_CSP_LEVELS_TV;
+            }
+        }
         if (params->primaries == MP_CSP_PRIM_AUTO) {
             // Guess based on the colormatrix as a first priority
             if (params->colorspace == MP_CSP_BT_2020_NC ||

video/out/opengl/video.c

@@ -2177,7 +2177,8 @@ static void pass_colormanage(struct gl_video *p, float peak_src,
         // We could pick any value we want here, the difference is just coding
         // efficiency.
         if (trc_orig == MP_CSP_TRC_SMPTE_ST2084 ||
-            trc_orig == MP_CSP_TRC_ARIB_STD_B67)
+            trc_orig == MP_CSP_TRC_ARIB_STD_B67 ||
+            trc_orig == MP_CSP_TRC_V_LOG)
         {
             trc_orig = MP_CSP_TRC_GAMMA22;
         }
@@ -2224,6 +2225,10 @@ static void pass_colormanage(struct gl_video *p, float peak_src,
         // target's reference peak
         if (trc_src == MP_CSP_TRC_ARIB_STD_B67)
             peak_src = 12 * peak_dst;
+
+        // Similar deal for V-Log
+        if (trc_src == MP_CSP_TRC_V_LOG)
+            peak_src = 46.0855 * peak_dst;
     }
 
     // All operations from here on require linear light as a starting point,

video/out/opengl/video_shaders.c

@@ -232,6 +232,12 @@ static const float B67_A = 0.17883277,
                    B67_B = 0.28466892,
                    B67_C = 0.55991073;
 
+// Common constants for Panasonic V-Log
+static const float VLOG_B = 0.00873,
+                   VLOG_C = 0.241514,
+                   VLOG_D = 0.598206,
+                   VLOG_R = 46.085527; // nominal peak
+
 // Linearize (expand), given a TRC as input
 void pass_linearize(struct gl_shader_cache *sc, enum mp_csp_trc trc)
 {
@@ -281,6 +287,16 @@ void pass_linearize(struct gl_shader_cache *sc, enum mp_csp_trc trc)
         // assume 1.0 is the maximum brightness, not the reference peak)
         GLSL(color.rgb /= vec3(12.0);)
         break;
+    case MP_CSP_TRC_V_LOG:
+        GLSLF("color.rgb = mix((color.rgb - vec3(0.125)) / vec3(5.6), \n"
+              "    pow(vec3(10.0), (color.rgb - vec3(%f)) / vec3(%f)) \n"
+              "              - vec3(%f),                              \n"
+              "    lessThanEqual(vec3(0.181), color.rgb));            \n",
+              VLOG_D, VLOG_C, VLOG_B);
+        // Same deal as with the B67 function, renormalize to texture range
+        GLSLF("color.rgb /= vec3(%f);\n", VLOG_R);
+        GLSL(color.rgb = clamp(color.rgb, 0.0, 1.0);)
+        break;
     default:
         abort();
     }
@@ -331,6 +347,14 @@ void pass_delinearize(struct gl_shader_cache *sc, enum mp_csp_trc trc)
               "                lessThan(vec3(1.0), color.rgb));\n",
               B67_A, B67_B, B67_C);
         break;
+    case MP_CSP_TRC_V_LOG:
+        GLSLF("color.rgb *= vec3(%f);\n", VLOG_R);
+        GLSLF("color.rgb = mix(vec3(5.6) * color.rgb + vec3(0.125),   \n"
+              "                vec3(%f) * log(color.rgb + vec3(%f))   \n"
+              "                    + vec3(%f),                        \n"
+              "                lessThanEqual(vec3(0.01), color.rgb)); \n",
+              VLOG_C / M_LN10, VLOG_B, VLOG_D);
+        break;
     default:
         abort();
     }