colorspace: add HDR10+ metadata to pl_hdr_metadata

Based on SMPTE ST2094, and in particular A/341 ATSC 2094-40. We should
keep track of this so we can add it to the metadata and use it for
things like ST2094-10 and ST2094-40.

We don't default these value if missing, because their presence should
indicate the availability of frame-specific metadata.

meson.build

@@ -12,6 +12,7 @@ project('libplacebo', ['c', 'cpp'],
     5,
     # API version
     {
+      '242': 'add `pl_hdr_metadata.scene_max/avg` and `pl_hdr_metadata.ootf`',
       '241': 'add `pl_plane_data.swapped`',
       '240': 'add `PL_COLOR_TRC_ST428`',
       '239': 'add `pl_fmt.planes` and `pl_tex.planes`',

src/colorspace.c

@@ -287,14 +287,29 @@ const struct pl_hdr_metadata pl_hdr_metadata_hdr10 ={
     .max_fall = 0, // unknown
 };
 
+static inline bool pl_hdr_bezier_equal(const struct pl_hdr_bezier *a,
+                                       const struct pl_hdr_bezier *b)
+{
+    return a->target_luma == b->target_luma &&
+           a->knee_x      == b->knee_x &&
+           a->knee_y      == b->knee_y &&
+           a->num_anchors == b->num_anchors &&
+           !memcmp(a->anchors, b->anchors, sizeof(a->anchors[0]) * a->num_anchors);
+}
+
 bool pl_hdr_metadata_equal(const struct pl_hdr_metadata *a,
                            const struct pl_hdr_metadata *b)
 {
     return pl_raw_primaries_equal(&a->prim, &b->prim) &&
            a->min_luma == b->min_luma &&
            a->max_luma == b->max_luma &&
            a->max_cll  == b->max_cll  &&
-           a->max_fall == b->max_fall;
+           a->max_fall == b->max_fall &&
+           a->scene_max[0] == b->scene_max[0] &&
+           a->scene_max[1] == b->scene_max[1] &&
+           a->scene_max[2] == b->scene_max[2] &&
+           a->scene_avg == b->scene_avg &&
+           pl_hdr_bezier_equal(&a->ootf, &b->ootf);
 }
 
 void pl_hdr_metadata_merge(struct pl_hdr_metadata *orig,
@@ -309,6 +324,12 @@ void pl_hdr_metadata_merge(struct pl_hdr_metadata *orig,
         orig->max_cll = update->max_cll;
     if (!orig->max_fall)
         orig->max_fall = update->max_fall;
+    if (!orig->scene_max[1])
+        memcpy(orig->scene_max, update->scene_max, sizeof(orig->scene_max));
+    if (!orig->scene_avg)
+        orig->scene_avg = update->scene_avg;
+    if (!orig->ootf.target_luma)
+        orig->ootf = update->ootf;
 }
 
 const struct pl_color_space pl_color_space_unknown = {0};
@@ -409,6 +430,10 @@ void pl_color_space_infer(struct pl_color_space *space)
         space->hdr.min_luma = space->sig_floor * PL_COLOR_SDR_WHITE;
         space->sig_floor = 0;
     }
+    if (space->sig_avg) {
+        space->hdr.scene_avg = space->sig_avg * PL_COLOR_SDR_WHITE;
+        space->sig_avg = 0;
+    }
 
 reinfer_peaks:
     if (space->hdr.max_luma < 1 || space->hdr.max_luma > 10000) {
@@ -448,6 +473,7 @@ void pl_color_space_infer(struct pl_color_space *space)
     if (space->sig_scale && !pl_color_transfer_is_hdr(space->transfer)) {
         space->hdr.max_luma *= space->sig_scale;
         space->hdr.min_luma *= space->sig_scale;
+        space->hdr.scene_avg *= space->sig_scale;
         space->sig_scale = 0;
     }
 

src/include/libplacebo/colorspace.h

@@ -328,17 +328,30 @@ void pl_raw_primaries_merge(struct pl_raw_primaries *orig,
 // Returns the raw primaries for a given color space.
 const struct pl_raw_primaries *pl_raw_primaries_get(enum pl_color_primaries prim);
 
+// Bezier curve for HDR metadata
+struct pl_hdr_bezier {
+    float target_luma;      // target luminance (cd/m²) for this OOTF
+    float knee_x, knee_y;   // cross-over knee point (0-1)
+    float anchors[15];      // intermediate bezier curve control points (0-1)
+    uint8_t num_anchors;
+};
+
 // Represents raw HDR metadata as defined by SMPTE 2086 / CTA 861.3, which is
 // often attached to HDR sources and can be forwarded to HDR-capable displays,
 // or used to guide the libplacebo built-in tone mapping.
 struct pl_hdr_metadata {
     // Mastering display metadata. This is used for tone-mapping.
-    struct pl_raw_primaries prim; // mastering display primaries
-    float min_luma, max_luma;     // min/max luminance (in cd/m²)
+    struct pl_raw_primaries prim;   // mastering display primaries
+    float min_luma, max_luma;       // min/max luminance (in cd/m²)
 
     // Content light level. This is ignored by libplacebo itself.
-    float max_cll;                // max content light level (in cd/m²)
-    float max_fall;               // max frame average light level (in cd/m²)
+    float max_cll;                  // max content light level (in cd/m²)
+    float max_fall;                 // max frame average light level (in cd/m²)
+
+    // HDR10+ dynamic metadata (per-scene)
+    float scene_max[3];             // maxSCL in cd/m² per component (RGB)
+    float scene_avg;                // average of maxRGB in cd/m²
+    struct pl_hdr_bezier ootf;      // reference OOTF (optional)
 };
 
 extern const struct pl_hdr_metadata pl_hdr_metadata_empty; // equal to {0}
@@ -389,7 +402,7 @@ struct pl_color_space {
     // Deprecated fields
     enum pl_color_light light PL_DEPRECATED;    // ignored
     float sig_peak PL_DEPRECATED;               // replaced by `hdr.max_luma`
-    float sig_avg PL_DEPRECATED;                // ignored
+    float sig_avg PL_DEPRECATED;                // replaced by `hdr.scene_avg`
     float sig_floor PL_DEPRECATED;              // replaced by `hdr.min_luma`
     float sig_scale PL_DEPRECATED;              // merged into `hdr.max/min_luma`
 };