vo_opengl: revise the transfer curve logic

Instead of hard-coding a big list, move some of the functionality
to csputils. Affects both the auto-guess blacklist and the peak
estimation.

Also update the comments.

video/csputils.c

@@ -437,6 +437,31 @@ struct mp_csp_primaries mp_get_csp_primaries(enum mp_csp_prim spc)
     }
 }
 
+// Get the relative peak of a transfer curve, that is: (source reference /
+// display reference), or 0 if there is none (i.e. source has an absolute peak)
+float mp_csp_trc_rel_peak(enum mp_csp_trc trc)
+{
+    switch (trc) {
+    case MP_CSP_TRC_SMPTE_ST2084: return 0.0; // This has a fixed peak
+    case MP_CSP_TRC_ARIB_STD_B67: return 12.0;
+    case MP_CSP_TRC_V_LOG:        return 46.0855;
+    }
+
+    return 1.0;
+}
+
+bool mp_trc_is_hdr(enum mp_csp_trc trc)
+{
+    switch (trc) {
+    case MP_CSP_TRC_SMPTE_ST2084:
+    case MP_CSP_TRC_ARIB_STD_B67:
+    case MP_CSP_TRC_V_LOG:
+        return true;
+    }
+
+    return false;
+}
+
 // Compute the RGB/XYZ matrix as described here:
 // http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
 static void mp_get_rgb2xyz_matrix(struct mp_csp_primaries space, float m[3][3])

video/csputils.h

@@ -219,6 +219,8 @@ int mp_chroma_location_to_av(enum mp_chroma_location mploc);
 void mp_get_chroma_location(enum mp_chroma_location loc, int *x, int *y);
 
 struct mp_csp_primaries mp_get_csp_primaries(enum mp_csp_prim csp);
+float mp_csp_trc_rel_peak(enum mp_csp_trc trc);
+bool mp_trc_is_hdr(enum mp_csp_trc trc);
 
 /* Color conversion matrix: RGB = m * YUV + c
  * m is in row-major matrix, with m[row][col], e.g.:

video/out/opengl/video.c

@@ -2206,31 +2206,24 @@ static void pass_colormanage(struct gl_video *p, float peak_src,
     }
 
     if (trc_dst == MP_CSP_TRC_AUTO) {
+        // Most people seem to complain when the image is darker or brighter
+        // than what they're "used to", so just avoid changing the gamma
+        // altogether by default. The only exceptions to this rule apply to
+        // very unusual TRCs, which even hardcode technoluddites would probably
+        // not enjoy viewing unaltered.
         trc_dst = p->image_params.gamma;
 
-        // Avoid outputting linear light or HDR content "by default"
-        if (trc_dst == MP_CSP_TRC_LINEAR ||
-            trc_dst == MP_CSP_TRC_SMPTE_ST2084 ||
-            trc_dst == MP_CSP_TRC_ARIB_STD_B67 ||
-            trc_dst == MP_CSP_TRC_V_LOG)
-        {
+        // Avoid outputting linear light or HDR content "by default". For these
+        // just pick gamma 2.2 as a default, since it's a good estimate for
+        // the response of typical displays
+        if (trc_dst == MP_CSP_TRC_LINEAR || mp_trc_is_hdr(trc_dst))
             trc_dst = MP_CSP_TRC_GAMMA22;
     }
-    }
 
     if (!peak_src) {
         // If the source has no information known, it's display-referred
         // (and should be treated relative to the specified desired peak_dst)
-        peak_src = peak_dst;
-
-        // Exception: ARIB STD-B67's nominal peak is exactly 12 times the
-        // target's reference peak
-        if (p->image_params.gamma == MP_CSP_TRC_ARIB_STD_B67)
-            peak_src = 12 * peak_dst;
-
-        // Similar deal for V-Log
-        if (p->image_params.gamma == MP_CSP_TRC_V_LOG)
-            peak_src = 46.0855 * peak_dst;
+        peak_src = peak_dst * mp_csp_trc_rel_peak(p->image_params.gamma);
     }
 
     // All operations from here on require linear light as a starting point,