vo_opengl: refactor HDR mechanism

Instead of doing HDR tone mapping on an ad-hoc basis inside
pass_colormanage, the reference peak of an image is now part of the
image params (alongside colorspace, gamma, etc.) and tone mapping is
done whenever peak_src != peak_dst.

To get sensible behavior when mixing HDR and SDR content and displays,
target-brightness is a generic filler for "the assumed brightness of SDR
content".

This gets rid of the weird display_scaled hack, sets the framework
for multiple HDR functions with difference reference peaks, and allows
us to (in a future commit) autodetect the right source peak from
the HDR metadata.

(Apart from metadata, the source peak can also be controlled via
vf_format. For HDR content this adjusts the overall image brightness,
for SDR content it's like simulating a different exposure)

1 files changed, 6 insertions, 11 deletions

diff --git a/video/out/opengl/video_shaders.c b/video/out/opengl/video_shaders.c
index d940c415e8..1f37f4fed1 100644
--- a/video/out/opengl/video_shaders.c
+++ b/video/out/opengl/video_shaders.c
@@ -313,15 +313,10 @@ void pass_delinearize(struct gl_shader_cache *sc, enum mp_csp_trc trc)
     }
 }
 
-// Tone map from one brightness to another
-void pass_tone_map(struct gl_shader_cache *sc, float peak_src, float peak_dst,
+// Tone map from a known peak brightness to the range [0,1]
+void pass_tone_map(struct gl_shader_cache *sc, float peak,
                    enum tone_mapping algo, float param)
 {
-    // First we renormalize to the output range
-    float scale = peak_src / peak_dst;
-    GLSLF("color.rgb *= vec3(%f);\n", scale);
-
-    // Then we use some algorithm to map back to [0,1]
     switch (algo) {
     case TONE_MAPPING_CLIP:
         GLSL(color.rgb = clamp(color.rgb, 0.0, 1.0);)
@@ -331,7 +326,7 @@ void pass_tone_map(struct gl_shader_cache *sc, float peak_src, float peak_dst,
         float contrast = isnan(param) ? 0.5 : param,
               offset = (1.0 - contrast) / contrast;
         GLSLF("color.rgb = color.rgb / (color.rgb + vec3(%f));\n", offset);
-        GLSLF("color.rgb *= vec3(%f);\n", (scale + offset) / scale);
+        GLSLF("color.rgb *= vec3(%f);\n", (peak + offset) / peak);
         break;
     }
 
@@ -342,20 +337,20 @@ void pass_tone_map(struct gl_shader_cache *sc, float peak_src, float peak_dst,
                A, C*B, D*E, A, B, D*F, E/F);
         GLSLHF("}\n");
 
-        GLSLF("color.rgb = hable(color.rgb) / hable(vec3(%f));\n", scale);
+        GLSLF("color.rgb = hable(color.rgb) / hable(vec3(%f));\n", peak);
         break;
     }
 
     case TONE_MAPPING_GAMMA: {
         float gamma = isnan(param) ? 1.8 : param;
         GLSLF("color.rgb = pow(color.rgb / vec3(%f), vec3(%f));\n",
-              scale, 1.0/gamma);
+              peak, 1.0/gamma);
         break;
     }
 
     case TONE_MAPPING_LINEAR: {
         float coeff = isnan(param) ? 1.0 : param;
-        GLSLF("color.rgb = vec3(%f) * color.rgb;\n", coeff / scale);
+        GLSLF("color.rgb = vec3(%f) * color.rgb;\n", coeff / peak);
         break;
     }