vo_opengl: implement support for OOTFs and non-display referred content

This introduces (yet another..) mp_colorspace members, an enum `light`
(for lack of a better name) which basically tells us whether we're
dealing with scene-referred or display-referred light, but also a bit
more metadata (in which way is the scene-referred light expected to be
mapped to the display?).

The addition of this parameter accomplishes two goals:

1. Allows us to actually support HLG more-or-less correctly[1]
2. Allows people playing back direct “camera” content (e.g. v-log or
   s-log2) to treat it as scene-referred instead of display-referred

[1] Even better would be to use the display-referred OOTF instead of the
idealized OOTF, but this would require either native HLG support in
LittleCMS (unlikely) or more communication between lcms.c and
video_shaders.c than I'm remotely comfortable with

That being said, in principle we could switch our usage of the BT.1886
EOTF to the BT.709 OETF instead and treat BT.709 content as being
scene-referred under application of the 709+1886 OOTF; which moves that
particular conversion from the 3dlut to the shader code; but also allows
a) users like UliZappe to turn it off and b) supporting the full HLG
OOTF in the same framework. But I think I prefer things as they are
right now.

1 files changed, 12 insertions, 0 deletions

diff --git a/video/csputils.h b/video/csputils.h
index 8e120922d7..9e81c90ebf 100644
--- a/video/csputils.h
+++ b/video/csputils.h
@@ -87,6 +87,17 @@ enum mp_csp_trc {
 
 extern const struct m_opt_choice_alternatives mp_csp_trc_names[];
 
+enum mp_csp_light {
+    MP_CSP_LIGHT_AUTO,
+    MP_CSP_LIGHT_DISPLAY,
+    MP_CSP_LIGHT_SCENE_HLG,
+    MP_CSP_LIGHT_SCENE_709_1886,
+    MP_CSP_LIGHT_SCENE_1_2,
+    MP_CSP_LIGHT_COUNT
+};
+
+extern const struct m_opt_choice_alternatives mp_csp_light_names[];
+
 // These constants are based on the ICC specification (Table 23) and match
 // up with the API of LittleCMS, which treats them as integers.
 enum mp_render_intent {
@@ -121,6 +132,7 @@ struct mp_colorspace {
     enum mp_csp_levels levels;
     enum mp_csp_prim primaries;
     enum mp_csp_trc gamma;
+    enum mp_csp_light light;
     float sig_peak; // highest relative value in signal. 0 = unknown/auto
 };