tone_mapping: make HDR metadata available to tone-mappers

By just sticking it inside `pl_hdr_metadata`, happen what may.

We don't need access to the output metadata, so omit it. (This will
probably never change, because this HDR metadata contains scene-derived
values)

meson.build

@@ -12,6 +12,7 @@ project('libplacebo', ['c', 'cpp'],
     5,
     # API version
     {
+      '245': 'add `pl_tone_map_params.hdr`',
       '244': 'add `pl_map_hdr_metadata`',
       '243': 'add `pl_color_space.nominal_min/max`',
       '242': 'add `pl_hdr_metadata.scene_max/avg` and `pl_hdr_metadata.ootf`',

src/include/libplacebo/tone_mapping.h

@@ -22,6 +22,7 @@
 #include <stdbool.h>
 
 #include <libplacebo/common.h>
+#include <libplacebo/colorspace.h>
 
 PL_API_BEGIN
 
@@ -93,6 +94,10 @@ struct pl_tone_map_params {
     // The desired characteristics of the output, in `output_scaling` units.
     float output_min;
     float output_max;
+
+    // The input HDR metadata. Only used by a select few tone-mapping
+    // functions. (Optional)
+    struct pl_hdr_metadata hdr;
 };
 
 #define pl_tone_map_params(...) (&(struct pl_tone_map_params) { __VA_ARGS__ });

src/shaders/colorspace.c

@@ -1285,6 +1285,7 @@ static void tone_map(pl_shader sh,
         .input_max = pl_hdr_rescale(PL_HDR_NORM, PL_HDR_SQRT, src_max),
         .output_min = dst_min,
         .output_max = dst_max,
+        .hdr = src->hdr,
     };
 
     enum pl_tone_map_mode mode = params->tone_mapping_mode;

src/tone_mapping.c

@@ -87,7 +87,8 @@ bool pl_tone_map_params_equal(const struct pl_tone_map_params *a,
            a->input_min == b->input_min &&
            a->input_max == b->input_max &&
            a->output_min == b->output_min &&
-           a->output_max == b->output_max;
+           a->output_max == b->output_max &&
+           pl_hdr_metadata_equal(&a->hdr, &b->hdr);
 }
 
 bool pl_tone_map_params_noop(const struct pl_tone_map_params *p)