Make HDR one fixed look with true blacks, and keep only its on switch and the three whites as settings.

HDR on is the game's scene through the observer-response mapper, anchored to the game's own mid grey and tone slope, with half of the hue bend of the game's clamp: the defaults the menu had. The tone mapper choice, the mid grey, the tone slope and its match, the hue clip, exposure, highlights, shadows, contrast, saturation, highlight saturation, blowout, flare, hue, grade and gamma are gone from the menu, the settings table and the example ini; a file that still sets them works as before, the keys read by nothing and logging nothing. The menu's HDR row is Off and On, with the peak, game and HUD whites under it. The game's own HDR is still there for a file that sets hdr = native, and the row lists it only then. The luminance mapper and its grading code, which no setting reaches any more, are removed from the tonemap library, and the support buffer carries one vec4 for it.

The dark tones of a dark scene sat far above black: the present showed the game's sRGB-encoded picture as that encode decodes, linear near black, while the game is graded for a display of gamma about 2.2, and since the observer-response mapper became the default the 2.2 correction ran with the luminance mapper only. A scene value of 0.003 came out at 0.29 nits at a white of 350 nits, where a 2.2 display shows the game at 0.015. The present now always shows the picture as a 2.2 display would, and the tonemap aims its peak lower by that correction's inverse, so the brightest light still reaches the display's peak; the same value comes out at 0.017 nits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/README-BuildKit.md

@@ -172,7 +172,7 @@ beside the game.
   FSR 3.1 on any card where `amd_fidelityfx_vk.dll` loads, FSR 4 on the Radeon cards AMD's FSR 4 libraries list it
   for), Frame generation (NVIDIA DLSS on RTX 40 and 50 cards, with
   a DLSS multiplier of 2x, or 3x and 4x on RTX 50 cards; FSR 3.1 on any card where it loads; it needs DLSS or FSR 3.1
-  upscaling on; the frame limit counts the frames the game draws and the generated ones come on top), HDR (the game's picture tone mapped to your display, with its own grading rows, or Native, the game's own HDR; turn HDR on in Windows first) and the
+  upscaling on; the frame limit counts the frames the game draws and the generated ones come on top), HDR (the game's picture tone mapped to your display, with its peak, game and HUD brightness; turn HDR on in Windows first) and the
   resolution. A setting that takes effect only when the game starts again says "after restart" once you change it,
   until you set it back, and the Restart button at the bottom then counts the settings waiting for it.
 - **Controls** in the menu has Button prompts: the game's own, or Xbox, PlayStation, Steam Deck or keyboard and mouse ones when