HDR: rename PaperWhiteNits to BrightnessNits, remove unified scanline bloom

- Rename shader UBO member PaperWhiteNits to BrightnessNits in HLSL
  and GLSL built-in HDR shaders
- Rename slang reflection semantic from PaperWhiteNits to BrightnessNits
  for custom shaders
- Remove UNIFIED_SCANLINE_BLOOM code path and kLuminanceWeights from
  Vulkan HDR shader, keeping per-channel bloom only
- Update Brightness menu description with alternative calibration tip
- Recompile Vulkan HDR SPIR-V

Author: MajorPainTheCactus

gfx/drivers/d3d_shaders/hdr_sm5.hlsl.h

@@ -6,7 +6,7 @@ SRC(
    float4x4 modelViewProj;
    float2 SourceSize;
    float2 OutputSize;
-   float paper_white_nits;   /* 200.0f   */
+   float brightness_nits;    /* 200.0f   */
    float max_nits;           /* 1000.0f  */
    uint subpixel_layout;     /* 0        */
    float scanlines;          /* 1.0f     */
@@ -192,13 +192,13 @@ float3 HDR10ToscRGB(float3 hdr10Color)
 }
 /* END Converted from (Copyright (c) Microsoft Corporation - Licensed under the MIT License.)  https://github.com/microsoft/Xbox-ATG-Samples/tree/master/Kits/ATGTK/HDR */
 
-float3 InverseTonemap(const float3 sdr_linear, const float max_nits, const float paper_white_nits)
+float3 InverseTonemap(const float3 sdr_linear, const float max_nits, const float brightness_nits)
 {
    const float input_val = max(sdr_linear.r, max(sdr_linear.g, sdr_linear.b));
 
    if (input_val < 0.0001f) return sdr_linear;
 
-   const float peak_ratio = max_nits / paper_white_nits;
+   const float peak_ratio = max_nits / brightness_nits;
 
    const float numerator = input_val;
    const float denominator = 1.0f - input_val * (1.0f - (1.0f / peak_ratio));
@@ -286,12 +286,12 @@ float4 To2020(const float4 sdr_linear)
 
 float3 HDR(const float3 sdr_linear)
 {
-   return InverseTonemap(sdr_linear, global.max_nits, global.paper_white_nits);
+   return InverseTonemap(sdr_linear, global.max_nits, global.brightness_nits);
 }
 
 float4 HDR(const float4 sdr_linear)
 {
-   const float3 hdr_linear = InverseTonemap(sdr_linear.rgb, global.max_nits, global.paper_white_nits);
+   const float3 hdr_linear = InverseTonemap(sdr_linear.rgb, global.max_nits, global.brightness_nits);
 
    return float4(hdr_linear, sdr_linear.a);
 }
@@ -304,7 +304,7 @@ float3 LinearToSignal(const float3 linear_colour)
 
 float3 HDR10(const float3 hdr_linear)
 {
-   const float3 pq_input  = hdr_linear * (global.paper_white_nits / kMaxNitsFor2084);
+   const float3 pq_input  = hdr_linear * (global.brightness_nits / kMaxNitsFor2084);
 
    const float3 hdr10 = LinearToST2084(max(pq_input, 0.0f));
 
@@ -313,7 +313,7 @@ float3 HDR10(const float3 hdr_linear)
 
 float4 HDR10(const float4 hdr_linear)
 {
-   const float3 pq_input  = hdr_linear.rgb * (global.paper_white_nits / kMaxNitsFor2084);
+   const float3 pq_input  = hdr_linear.rgb * (global.brightness_nits / kMaxNitsFor2084);
 
    const float3 hdr10 = LinearToST2084(max(pq_input, 0.0f));
 
@@ -516,7 +516,7 @@ float4 PSMain(PSInput input) : SV_TARGET
           * scRGB units: 1.0 = 80 nits. */
          float3 linear_col = Scanlines(input.texcoord);
 
-         return float4(linear_col * (global.paper_white_nits / kscRGBWhiteNits), 1.0f);
+         return float4(linear_col * (global.brightness_nits / kscRGBWhiteNits), 1.0f);
       }
       else
       {

gfx/drivers/vulkan_shaders/hdr.frag

@@ -15,11 +15,9 @@ const float kPi                    = 3.1415926536;
 const float kEuler                 = 2.718281828459;
 const float kMax                   = 1.0;
 
-#define UNIFIED_SCANLINE_BLOOM
 
 const float kBeamWidth             = 0.5;
 
-const vec3 kLuminanceWeights       = vec3(0.2126, 0.7152, 0.0722);
 
 const uint kChannelMask           = 3u;
 const uint kFirstChannelShift     = 2u;
@@ -188,7 +186,7 @@ vec3 LinearToSignal(const vec3 linear_colour)
 
 vec3 HDR10(const vec3 hdr_linear)
 {
-   vec3 pq_input  = hdr_linear * vec3(global.PaperWhiteNits / kMaxNitsFor2084);
+   vec3 pq_input  = hdr_linear * vec3(global.BrightnessNits / kMaxNitsFor2084);
 
    vec3 hdr10 = LinearToST2084(max(pq_input, vec3(0.0f)));
 
@@ -197,7 +195,7 @@ vec3 HDR10(const vec3 hdr_linear)
 
 vec4 HDR10(const vec4 hdr_linear)
 {
-   vec3 pq_input  = hdr_linear.rgb * vec3(global.PaperWhiteNits / kMaxNitsFor2084);
+   vec3 pq_input  = hdr_linear.rgb * vec3(global.BrightnessNits / kMaxNitsFor2084);
 
    vec3 hdr10 = LinearToST2084(max(pq_input, vec3(0.0f)));
 
@@ -258,30 +256,6 @@ vec3 ScanlineColour(const vec2 tex_coord,
    float distance_adjusted          = max(0.0, raw_distance);
    float effective_distance         = distance_adjusted * 2.0;
 
-#ifdef UNIFIED_SCANLINE_BLOOM
-   /* Unified bloom: compute a single horizontal interpolation from luminance
-    * so the scanline envelope is shared across all channels in the phosphor
-    * triad, preventing colour shifts from per-channel bloom differences. */
-   float lum_0                      = dot(signal_0, kLuminanceWeights);
-   float lum_1                      = dot(signal_1, kLuminanceWeights);
-   float lum_horiz_interp           = Bezier(narrowed_source_pixel_offset, BeamControlPoints(beam_attack, lum_0 > lum_1));
-   float beam_intensity             = clamp(mix(lum_0, lum_1, lum_horiz_interp), 0.0, 1.0);
-
-   float beam_width                 = mix(scanline_min, scanline_max, beam_intensity);
-   float scanline_dist              = clamp(effective_distance / beam_width, 0.0, 1.0);
-   vec4 control_points              = vec4(1.0, 1.0, beam_intensity * scanline_attack, 0.0);
-   float envelope                   = Bezier(scanline_dist, control_points);
-
-   for(int ch = 0; ch < 3; ch++)
-   {
-      float horiz_interp            = Bezier(narrowed_source_pixel_offset, BeamControlPoints(beam_attack, signal_0[ch] > signal_1[ch]));
-      float signal_channel          = mix(signal_0[ch], signal_1[ch], horiz_interp);
-
-      result[ch] = envelope * signal_channel;
-   }
-#else
-   /* Per-channel bloom: each channel computes its own scanline envelope based on
-    * its individual brightness (models independent electron gun bloom). */
    for(int ch = 0; ch < 3; ch++)
    {
       float horiz_interp               = Bezier(narrowed_source_pixel_offset, BeamControlPoints(beam_attack, signal_0[ch] > signal_1[ch]));
@@ -298,7 +272,6 @@ vec3 ScanlineColour(const vec2 tex_coord,
 
       result[ch] = luminance * signal_channel;
    }
-#endif
 
    return result;
 }
@@ -418,15 +391,15 @@ void main()
    {
       /* scRGB mode: sRGB to linear for scRGB / HDR16 swapchain.
        * Scale by MaxNits / kscRGBWhiteNits because scRGB 1.0 = 80 nits.
-       * Using MaxNits (not PaperWhiteNits) so the SDR UI fills the
+       * Using MaxNits (not BrightnessNits) so the SDR UI fills the
        * display's native range, preserving tonal balance uniformly. */
       if((global.Scanlines > 0.0) && (global.OutputSize.y > 240.0 * 4.0))
       {
          /* Scanlines() returns linear Rec.709 with mask already applied in Rec.709 space.
           * scRGB units: 1.0 = 80 nits. */
          vec3 linear = Scanlines(vTexCoord);
 
-         FragColor = vec4(linear * (global.PaperWhiteNits / kscRGBWhiteNits), 1.0);
+         FragColor = vec4(linear * (global.BrightnessNits / kscRGBWhiteNits), 1.0);
       }
       else
       {